Opioid receptors mediate the acquisition, but not the expression of mitragynine-induced conditioned place preference in rats

[Kratom-From natural remedy to addictive drug and back]

BACKGROUND

Kratom/ketum is a psychoactive herbal preparation that has been used for a long time as a remedy and performance-enhancing substance in Southeast Asia. The advancement of globalization is making kratom increasingly more available in the western world, where it is becoming increasingly more used.

OBJECTIVE

The current research on kratom and its ingredients is presented.

MATERIAL AND METHODS

An overview of the use and effects of kratom is exemplary given on the basis of reports. The instrumentalization of the drug and its consequences up to the development of addiction are discussed.

RESULTS

Consumption is accompanied by several instrumentalizeable effects so that kratom is used as a therapeutic substance in the self-management of pain, anxiety and depression as well as other substance addictions. Another benefit comes from the performance-enhancing effects on physical work and in a social context. Consumption is usually well controlled, rarely escalates and has few and mostly mild aversive side effects. The danger arises from consumption particularly when there is an escalation of the dose and from mixed consumption with other psychoactive substances. The main alkaloid mitragynine and the more potent 7‑hydroxy-mitragynine are considered mainly responsible for the effect. Both have a complex pharmacology that involves partial µ‑opioid receptor agonism.

DISCUSSION

Epidemiological, clinical and neurochemical studies have shown that kratom only has a limited addictive drug profile, which might suggest a medical use as a remedy or substitute in addiction treatment.

Kratom (Mitragyna speciosa) Use and Mental Health: A Systematic Review and Multilevel Meta-Analysis

INTRODUCTION

Kratom (Mitragyna speciosa) is a medicinal tree native to Southeast Asia. The present multilevel meta-analysis describes the association between kratom use and the positive and negative indicators of mental health.

METHODS

A total of thirty-six articles were included in the meta-analysis to examine the associations, using a random-effects model.

RESULTS

The pooled effect size showed a very small positive association between kratom use and negative indicators of mental health {r = 0.092, 95% confidence interval (CI) = [0.020, 0.164], p < 0.05}, while no significant association was found with positive indicators of mental health (r = -0.031, 95% CI = [-0.149, 0.087], p > 0.05). Pooled effect sizes of specific mental health outcomes indicated that kratom use showed only a small positive correlation with externalizing disorders (r = 0.201, 95% CI = [0.107, 0.300], p < 0.001). No significant association was found between kratom use and quality of life (r = 0.069, 95% CI = [-0.104, 0.242], p > 0.05) and internalizing disorders (r = -0.001, 95% CI = [-0.115, 0.095], p > 0.05). Multilevel moderator analysis showed that the pooled effect size of the association between kratom use and substance use disorder was stronger in Malaysia (r = 0.347, 95% CI = [0.209, 0.516], p < 0.001), and with the mean age (β1 = -0.035, 95% CI = [-0.055, -0.014], p = 0.003), and the drug profile of those who were not co-using other drugs (r = 0.347, 95% CI = [0.209, 0.516], p < 0.001).

CONCLUSION

The meta-analysis supports the kratom instrumentalization concept, in that a positive gain from kratom consumption can be achieved without any significant adverse associations with mental health.

The dopamine D1 receptor antagonist SCH-23390 blocks the acquisition, but not expression of mitragynine-induced conditioned place preference in rats

Mitragynine (MG) is the primary active constituent of Mitragyna speciosa Korth (kratom), a psychoactive Southeast Asian plant with potential therapeutic use. Numerous studies support roles of dopaminergic system in drug reward. However, the involvement of the dopaminergic system in mediating MG reward and drug-seeking is poorly understood. Using conditioned place preference (CPP) paradigm, the present study aims to evaluate the roles of the dopamine (DA) D1 receptor in the acquisition and expression of MG-induced CPP in rats. The effects of SCH-23390, a selective DA D1 receptor antagonist, on the acquisition of MG-induced CPP were first investigated. Rats were pre-treated systemically with SCH-23390 (0, 0.1 and 0.3 mg/kg, i.p.) prior to MG (10 mg/kg) conditioning sessions. Next, we tested the effects of the DA D1 receptor antagonist on the expression of MG-induced CPP. Furthermore, the effects of a MG-priming dose (5 mg/kg) on the reinstatement of extinguished CPP were tested. The results showed that SCH-23390 dose-dependently suppressed the acquisition of a MG-induced CPP. In contrast, SCH-23390 had no effect on the expression of a MG-induced CPP. The findings of this study suggested a crucial role of the DA D1 receptor in the acquisition, but not the expression of the rewarding effects of MG in a CPP test. Furthermore, blockade of the D1-like receptor during conditioning did not prevent MG priming effects on CPP reinstatement test, suggesting no role for the DA D1 receptor in reinstatement sensitivity.

Mitragynine, a primary constituent of kratom reinstates morphine-seeking behaviour in rats

Mitragynine (MG) is a pharmacologically active alkaloid derived from the leaves of Mitragyna speciosa Korth (Kratom). This plant has sparked significant interest as a potential alternative treatment for managing opioid dependence and withdrawal due to its opioid-like pharmacological effects. However, whether MG exposure would trigger opioid-seeking behaviour following abstinence has not been investigated. The present study examined the effects of MG priming on morphine-seeking behaviour in rats. Male Sprague-Dawley rats were initially trained to intravenously self-administer morphine (0.5 mg/kg/infusion) under a fixed ratio-3 schedule of reinforcement. Removal of both morphine infusions and drug-associated cues led to the subsequent extinction of the drug-seeking behaviour. Tests of reinstatement were made following exposure to a randomised order of intraperitoneal injections of MG (3, 10 and 30 mg/kg), morphine (5 mg/kg) and vehicle. Significant levels of drug-seeking behaviour were observed following extended access to morphine self-administration, which was extinguished following removal of morphine and cues indicative of morphine-seeking behaviour, supporting the relapse model. The present finding demonstrated that MG priming in a dose of 10 mg/kg resulted in the reinstatement of morphine-seeking behaviour, whereas the higher MG dose (30 mg/kg) tested suppressed the seeking response. This study indicated that exposure to a low MG dose may increase the likelihood of relapsing to opioids, suggesting that the potential of MG as a treatment for opioid management merits further scientific assessment of its ability to trigger relapse to opioid abuse.

The role of AMPA and NMDA receptors in mitragynine effects on hippocampal synaptic plasticity

Mitragynine, an indole alkaloid from the plant Mitragyna speciosa (Kratom), has been reported to modify hippocampal synaptic transmission. However, the role of glutamatergic neurotransmission modulating synaptic plasticity in mitragynine-induced synaptic changes is still unknown. Here, we determined the role of AMPA- and NMDA glutamate receptors in mitragynine-induced synaptic plasticity in the hippocampus. Male Sprague Dawley rats received either vehicle or mitragynine (10 mg/kg), with or without the AMPA receptor antagonist, NBQX (3 mg/kg), or the NMDA receptor antagonist, MK-801 (0.2 mg/kg). Field excitatory postsynaptic potentials (fEPSP) during baseline, paired-pulse facilitation (PPF) and long-term potentiation (LTP) were recorded in-vivo in the hippocampal CA1 area of anaesthetised rats. Basal synaptic transmission and LTP were significantly impaired after mitragynine, NBQX, and MK-801 alone, without an effect on PPF. Combined effects suggest a weak functional AMPA- as well as NMDA receptor antagonist action of mitragynine.

Kratom: Substance of Abuse or Therapeutic Plant?

Kratom is the common term for Mitragyna speciosa and its products. Its major active compounds are mitragynine and 7-hydroxymitragynine. An estimated 2.1 million US residents used kratom in 2020, as a "legal high" and self-medication for pain, opioid withdrawal, and other conditions. Up to 20% of US kratom users report symptoms consistent with kratom use disorder. Kratom use is associated with medical toxicity and death. Causality is difficult to prove as almost all cases involve other psychoactive substances. Daily, high-dose use may result in kratom use disorder and opioid-like withdrawal on cessation of use. These are best treated with buprenorphine.

Kratom alkaloid mitragynine: Inhibition of chemotherapy-induced peripheral neuropathy in mice is dependent on sex and active adrenergic and opioid receptors

Mitragynine (MG) is an alkaloid found in Mitragyna speciosa (kratom) that is used as an herbal remedy for pain relief and opioid withdrawal. MG acts at μ-opioid and α-adrenergic receptors in vitro, but the physiological relevance of this activity in the context of neuropathic pain remains unknown. The purpose of the present study was to characterize the effects of MG in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN), and to investigate the potential impact of sex on MG's therapeutic efficacy. Inhibition of oxaliplatin-induced mechanical hypersensitivity was measured following intraperitoneal administration of MG. Both male and female C57BL/6J mice were used to characterize potential sex-differences in MG's therapeutic efficacy. Pharmacological mechanisms of MG were characterized through pretreatment with the opioid and adrenergic antagonists naltrexone, prazosin, yohimbine, and propranolol (1, 2.5, 5 mg/kg). Oxaliplatin produced significant mechanical allodynia of equal magnitude in both male and females, which was dose-dependently attenuated by repeated MG exposure. MG was more potent in males vs females, and the highest dose of MG (10 mg/kg) exhibited greater anti-allodynic efficacy in males. Mechanistically, activity at µ-opioid, α₁- and α₂-adrenergic receptors, but not β-adrenergic receptors contributed to the effects of MG against oxaliplatin-induced mechanical hypersensitivity. Repeated MG exposure significantly attenuated oxaliplatin-induced mechanical hypersensitivity with greater potency and efficacy in males, which has crucial implications in the context of individualized pain management. The opioid and adrenergic components of MG indicate that it shares pharmacological properties with clinical neuropathic pain treatments.

Searching for a Signal: Self-Reported Kratom Dose-Effect Relationships Among a Sample of US Adults With Regular Kratom Use Histories

There is limited understanding regarding kratom use among US adults. Although motivations for use are increasingly understood, typical kratom doses, threshold of (low and high) doses for perceived effectiveness, and effects produced during cessation are not well documented. We aimed to extend prior survey work by recruiting adults with current and past kratom exposure. Our goal was to better understand kratom dosing, changes in routines, and perception of effects, including time to onset, duration, and variability of beneficial and adverse outcomes from use and cessation. Among respondents who reported experiencing acute kratom effects, we also sought to determine if effects were perceived as helpful or unhelpful in meeting daily obligations. Finally, we attempted to detect any signal of a relationship between the amount of kratom consumed weekly and weeks of regular use with ratings of beneficial effects from use and ratings of adverse effects from cessation. We conducted an online survey between April-May 2021 by re-recruiting participants from a separate study who reported lifetime kratom use. A total of 129 evaluable surveys were collected. Most (59.7%) had used kratom >100 times and reported currently or having previously used kratom >4 times per week (62 weeks on average). Under half (41.9%) reported that they considered themselves to be a current "regular kratom user." A majority (79.8%) reported experiencing acute effects from their typical kratom dose and that onset of effects began in minutes but dissipated within hours. Over a quarter reported that they had increased their kratom dose since use initiation, whereas 18.6% had decreased. Greater severity of unwanted effects from ≥1 day of kratom cessation was predicted by more weeks of regular kratom use (β = 6.74, p = 0.02). Acute kratom effects were largely reported as compatible with, and sometimes helpful in, meeting daily obligations. In the absence of human laboratory studies, survey methods must be refined to more precisely assess dose-effect relationships. These can help inform the development of controlled observational and experimental studies needed to advance the public health understanding of kratom product use.

Ameliorative effects of alkaloid extract from Mitragyna speciosa (Korth.) Havil. Leaves on methamphetamine conditioned place preference in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Mitragyna speciosa (Korth.) Havil., popularly known as Kratom (KT), is a medicinal plant used for pain suppression in Southeast Asia. It has been claimed to assist drug users withdraw from methamphetamine (METH) dependence. However, its use was controversial and not approved yet.

AIM OF THE STUDY

This study was conducted to characterize local field potential (LFP) patterns in the nucleus accumbens (NAc) and the hippocampus (HP) in mice with METH conditioned place preference (CPP) that were treated with KT alkaloid extract.

MATERIALS AND METHODS

Male Swiss albino ICR mice were implanted with intracraneal electrodes into the NAc and HP. To induce METH CPP, animals were injected intraperitoneally once a day with METH (1 mg/kg) and saline (0.9% w/v) alternately and put into METH/saline compartments to experience the associations between drug/saline injection and the unique environmental contexts for 10 sessions. Control group received saline injection paired with both saline/saline compartments. On post-conditioning day, effects of 40 (KT40), 80 (KT80) mg/kg KT alkaloid extract and 20 mg/kg bupropion (BP) on CPP scores and LFP powers and NAc-HP coherence were tested.

RESULTS

Two-way ANOVA revealed significant induction of CPP by METH sessions (P < 0.01). Multiple comparisons indicated that METH CPP was completely abolished by KT80 (P < 0.001). NAc gamma I (30.0-44.9 Hz) and HP delta (1.0-3.9 Hz) powers were significantly increased in mice with METH CPP (P < 0.01). The elevated NAc gamma I was significantly suppressed by KT80 (P < 0.05) and the increased HP delta was significantly reversed by KT40 (P < 0.01) and KT80 (P < 0.001). In addition, NAc-HP coherence was also significantly increased in gamma I (30.0-44.9 Hz) frequency range (P < 0.05) but it was reversed by KT80 (P < 0.05). Treatment with BP did not produce significant effect on these parameters.

CONCLUSIONS

These findings demonstrated that KT alkaloid extract significantly reversed CPP scores and LFP patterns induced by METH administration. The ameliorative effects of the extract might be beneficial for treatment of METH craving and addiction.

Analgesic Opioid Ligand Discovery Based on Nonmorphinan Scaffolds Derived from Natural Sources

Strong opioid analgesics, including morphine, are the mainstays for treating moderate to severe acute pain and alleviating chronic cancer pain. However, opioid-related adverse effects, including nausea or vomiting, sedation, respiratory depression, constipation, pruritus (itch), analgesic tolerance, and addiction and abuse liability, are problematic. In addition, the use of opioids to relieve chronic noncancer pain is controversial due to the "opioid crisis" characterized by opioid misuse or abuse and escalating unintentional death rates due to respiratory depression. Hence, considerable research internationally has been aimed at the "Holy Grail" of the opioid analgesic field, namely the discovery of novel and safer opioid analgesics with improved opioid-related adverse effects. In this Perspective, medicinal chemistry strategies are addressed, where structurally diverse nonmorphinan-based opioid ligands derived from natural sources were deployed as lead molecules. The current state of play, clinical or experimental status, and novel opioid ligand discovery approaches are elaborated in the context of retaining analgesia with improved safety and reduced adverse effects, especially addiction liability.

Mitragynine improves cognitive performance in morphine-withdrawn rats

RATIONALE

The treatment of opiate addiction is an unmet medical need. Repeated exposure to opiates disrupts cognitive performance. Opioid substitution therapy, with, e.g., methadone, may further exacerbate the cognitive deficits. Growing evidence suggests that mitragynine, the primary alkaloid from the Kratom (Mitragyna speciosa) leaves, may serve as a promising alternative therapy for opiate addiction. However, the knowledge of its health consequences is still limited.

OBJECTIVES

We aimed to examine the cognitive effects of mitragynine substitution in morphine-withdrawn rats. Furthermore, we asked whether neuronal addiction markers like the brain-derived neurotrophic factor (BDNF) and Ca²⁺/calmodulin-dependent kinase II alpha (αCaMKII) might mediate the observed effects.

METHODS

Male Sprague-Dawley rats were given morphine at escalating doses before treatment was discontinued to induce a spontaneous morphine withdrawal. Then, vehicle or mitragynine (5 mg/kg, 15 mg/kg, or 30 mg/kg) substitution was given for 3 days. A vehicle-treated group was used as a control. Withdrawal signs were scored after 24 h, 48 h, and 72 h, while novel object recognition (NOR) and attentional set-shifting (ASST) were tested during the substitution period.

RESULTS

Discontinuation of morphine significantly induced morphine withdrawal signs and cognitive deficit in the ASST. The substitution with mitragynine was able to alleviate the withdrawal signs. Mitragynine did not affect the recognition memory in the NOR but significantly improved the reversal learning deficit in the morphine-withdrawn rats.

CONCLUSIONS

These data support the idea that mitragynine could be used as safe medication therapy to treat opiate addiction with beneficial effects on cognitive deficits.

In vitro and in vivo pharmacology of kratom

Kratom products have been historically and anecdotally used in south Asian countries for centuries to manage pain and opioid withdrawal. The use of kratom products has dramatically increased in the United States. More than 45 kratom alkaloids have been isolated, yet the overall pharmacology of the individual alkaloids is still not well characterized. The purpose of this chapter is to summarize in vitro and in vivo opioid activities of the primary kratom alkaloid mitragynine and its more potent metabolite 7-hydroxymitragynine. Following are experimental procedures described to characterize opioid receptor activity; receptor binding and functional assays, antinociceptive assays, operant conditioning assays, and respiratory plethysmography. The capacity of kratom alkaloids to confer tolerance and physical dependence as well as their pharmacokinetic properties are also summarized. The data reviewed here suggest that kratom products and mitragynine possess low efficacy agonist activity at the mu-opioid receptor in vivo. In addition, kratom products and mitragynine have been demonstrated to antagonize the effects of high efficacy mu-opioid agonists. The data further suggest that 7-hydroxymitragynine formed in vivo by metabolism of mitragynine may be minimally involved in the overall behavioral profile of mitragynine and kratom, whereas 7-hydroxymitragynine itself, at sufficiently high doses administered exogenously, shares many of the same abuse- and dependence-related behavioral effects associated with traditional opioid agonists. The apparent low efficacy of kratom products and mitragynine at mu-opioid receptors supports the development of these ligands as effective and potentially safe medications for opioid use disorder.

Oxidative Metabolism as a Modulator of Kratom's Biological Actions

The leaves of Mitragyna speciosa (kratom), a plant native to Southeast Asia, are increasingly used as a pain reliever and for attenuation of opioid withdrawal symptoms. Using the tools of natural products chemistry, chemical synthesis, and pharmacology, we provide a detailed in vitro and in vivo pharmacological characterization of the alkaloids in kratom. We report that metabolism of kratom's major alkaloid, mitragynine, in mice leads to formation of (a) a potent mu opioid receptor agonist antinociceptive agent, 7-hydroxymitragynine, through a CYP3A-mediated pathway, which exhibits reinforcing properties, inhibition of gastrointestinal (GI) transit and reduced hyperlocomotion, (b) a multifunctional mu agonist/delta-kappa antagonist, mitragynine pseudoindoxyl, through a CYP3A-mediated skeletal rearrangement, displaying reduced hyperlocomotion, inhibition of GI transit and reinforcing properties, and (c) a potentially toxic metabolite, 3-dehydromitragynine, through a non-CYP oxidation pathway. Our results indicate that the oxidative metabolism of the mitragynine template beyond 7-hydroxymitragynine may have implications in its overall pharmacology in vivo.

The effect of mitragynine on extracellular activity of brain dopamine and its metabolites

Kratom, derived from the plant Mitragyna speciosa (M. speciosa) Korth is a traditional psychoactive preparation widely used in Southeast Asia and increasingly in the rest of the world. Use and abuse of Kratom preparations can be attributed to mitragynine (MIT), the main psychoactive compound isolated from its leaves. While MIT may have beneficial effects as a recreational drug, for pain management, and for opiate withdrawal, it may have an addiction potential at higher doses. However, its action in the reward system of the brain is currently unknown. This study investigated how mitragynine (10 mg/kg, i.p.) affects extracellular activity of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the prefrontal cortex (PFC), nucleus accumbens (NAc) and caudate putamen (CPu) of the brain, compared to morphine (MOR; 10 mg/kg, i.p.) and methamphetamine (METH; 10 mg/kg, i.p.). Using in-vivo microdialysis in freely moving rats, we found a significant increase of extracellular DA after MOR and METH, but not after MIT in all three brain regions. MIT led to a significant increase of DOPAC and/or HVA in these brain regions while MOR and METH had only moderate effects. These findings suggest a strong and prolonged effect of MIT on DA synthesis/metabolism, but not on extracellular DA activity, which may limit the addiction risk of MIT, in contrast to MOR and METH.

Mitragynine (Kratom)-Induced Cognitive Impairments in Mice Resemble Δ9-THC and Morphine Effects: Reversal by Cannabinoid CB1 Receptor Antagonism

Kratom is a widely abused plant-based drug preparation with a global interest in recent years, well beyond its native grounds in Southeast Asia. Mitragynine, its major psychoactive constituent is known to exhibit opioid-like behavioral effects with resultant neuroplasticity in the brain reward system. Its chronic administration is associated with cognitive impairments in animal studies. However, the underlying molecular mechanism for such a deficit remains elusive. In this study, the involvement of cannabinoid type-1 (CB₁) receptors in cognitive deficits after chronic mitragynine exposures was investigated for 28 days (with incremental dose sensitization from 1 to 25 mg/kg) in adult male Swiss albino mice using the IntelliCage^® system. Chronic high-dose mitragynine exposure (5–25 mg/kg, intraperitoneal [i.p.]), but not low-dose exposure (1–4 mg/kg, i.p.), induced hyperlocomotion, potentiated the preference for sucrose reward, increased resistance to punishment, and impaired place learning and its reversal. Comparable deficits were also observed after chronic treatments with Δ-9-tetrahydrocannabinol (THC, 2 mg/kg, i.p.) or morphine (5 mg/kg, subcutaneous). Mitragynine-, morphine-, and THC-induced learning and memory deficits were reversed by co-treatment with the CB₁ receptor antagonist, NIDA-41020 (10 mg/kg, i.p.). A significant upregulation of CB₁ receptor expression was found in the hippocampal CA1 region and ventral tegmental area after chronic high-dose mitragynine and morphine, whereas a downregulation was observed after chronic THC. In conclusion, the present study suggests a plausible role of the CB₁ receptor in mediating the dose-dependent cognitive deficits after chronic high-dose mitragynine exposure. This also highlights the potential of CB₁ receptor antagonism in ameliorating the cognitive deficits associated with long-term kratom/mitragynine consumption in humans.

The Antidepressant-Like and Analgesic Effects of Kratom Alkaloids are accompanied by Changes in Low Frequency Oscillations but not ΔFosB Accumulation

Mitragyna speciosa (“kratom”), employed as a traditional medicine to improve mood and relieve pain, has shown increased use in Europe and North America. Here, the dose-dependent effects of a purified alkaloid kratom extract on neuronal oscillatory systems function, analgesia, and antidepressant-like behaviour were evaluated and kratom-induced changes in ΔFosB expression determined. Male rats were administered a low or high dose of kratom (containing 0.5 or 1 mg/kg of mitragynine, respectively) for seven days. Acute or repeated low dose kratom suppressed ventral tegmental area (VTA) theta oscillatory power whereas acute or repeated high dose kratom increased delta power, and reduced theta power, in the nucleus accumbens (NAc), prefrontal cortex (PFC), cingulate cortex (Cg) and VTA. The repeated administration of low dose kratom additionally elevated delta power in PFC, decreased theta power in NAc and PFC, and suppressed beta and low gamma power in Cg. Suppressed high gamma power in NAc and PFC was seen selectively following repeated high dose kratom. Both doses of kratom elevated NAc-PFC, VTA-NAc, and VTA-Cg coherence. Low dose kratom had antidepressant-like properties whereas both doses produced analgesia. No kratom-induced changes in ΔFosB expression were evident. These results support a role for kratom as having both antidepressant and analgesic properties that are accompanied by specific changes in neuronal circuit function. However, the absence of drug-induced changes in ΔFosB expression suggest that the drug may circumvent this cellular signaling pathway, a pathway known for its significant role in addiction.

Methadone, Buprenorphine, and Clonidine Attenuate Mitragynine Withdrawal in Rats

Background: Kratom or Mitragyna speciosa Korth has been widely used to relieve the severity of opioid withdrawal in natural settings. However, several studies have reported that kratom may by itself cause dependence following chronic consumption. Yet, there is currently no formal treatment for kratom dependence. Mitragynine, is the major psychoactive alkaloid in kratom. Chronic mitragynine treatment can cause addiction-like symptoms in rodent models including withdrawal behaviour. In this study we assessed whether the prescription drugs, methadone, buprenorphine and clonidine, could mitigate mitragynine withdrawal effects. In order to assess treatment safety, we also evaluated hematological, biochemical and histopathological treatment effects. Methods: We induced mitragynine withdrawal behaviour in a chronic treatment paradigm in rats. Methadone (1.0 mg/kg), buprenorphine (0.8 mg/kg) and clonidine (0.1 mg/kg) were i.p. administered over four days during mitragynine withdrawal. These treatments were stopped and withdrawal sign assessment continued. Thereafter, toxicological profiles of the treatments were evaluated in the blood and in organs. Results: Chronic mitragynine treatment caused significant withdrawal behaviour lasting at least 5 days. Methadone, buprenorphine, as well as clonidine treatments significantly attenuated these withdrawal signs. No major effects on blood or organ toxicity were observed. Conclusion: These data suggest that the already available prescription medications methadone, buprenorphine, and clonidine are capable to alleviate mitragynine withdrawal signs rats. This may suggest them as treatment options also for problematic mitragynine/kratom use in humans.

Kratom pharmacology: Clues from planarians exposed to mitragynine

Mitragynine (MG), the most prevalent bioactive alkaloid in kratom, displays nanomolar affinity for µ, κ and δ opioid receptors and produces opioid-dependent antinociception and dependence in rats. Here, using a battery of behavioral assays, we investigated MG effects in planarians. Acute MG exposure (< 100 μM) did not affect planarian motility or environmental preference, but reduced motility was detected during abstinence from chronic MG (1, 10 μM). MG (10 μM) produced place conditioning effects that were reduced by naltrexone (10  μΜ). These results suggest that MG produces opioid-sensitive reinforcing effects in planarians and MG pharmacology is conserved across different species.

Proteomic analysis reveals brain Rab35 as a potential biomarker of mitragynine withdrawal in rats

Mitragyna speciosa, also known as kratom, has been used for mitigating the severity of opioid withdrawal in humans. Its main indole alkaloid, mitragynine, has been considered as a pharmacotherapy for pain conditions and opioid replacement therapy. However, at high doses, chronic mitragynine may also have an addiction potential. The effects of chronic action of mitragynine in the brain are still unknown. The present study developed a mitragynine withdrawal model in rats and used it for a proteomic analysis of mitragynine withdrawal effects. Mitragynine (30 mg/kg, i.p.) was administered daily over a period of 14 days and then withdrawn. A proteomic analysis revealed that from a total of 1524 proteins identified, 31 proteins were upregulated, and 3 proteins were downregulated in the mitragynine withdrawal model. The Rab35 protein expression increased most profoundly in the mitragynine withdrawal group as compared to vehicle group. Therefore, it is proposed that Rab35 in the brain might be considered as a potential biomarker during mitragynine withdrawal and might be valuable target protein in developing new pharmacotherapies in the future.

Psychoactive Substances of Natural Origin: Toxicological Aspects, Therapeutic Properties and Analysis in Biological Samples

The consumption of new psychoactive substances (NPSs) has been increasing, and this problem affects several countries worldwide. There is a class of NPSs of natural origin, consisting of plants and fungi, which have a wide range of alkaloids, responsible for causing relaxing, stimulating or hallucinogenic effects. The consumption of some of these substances is prompted by religious beliefs and cultural reasons, making the legislation very variable or even ambiguous. However, the abusive consumption of these substances can present an enormous risk to the health of the individuals, since their metabolism and effects are not yet fully known. Additionally, NPSs are widely spread over the internet, and their appearance is very fast, which requires the development of sophisticated analytical methodologies, capable of detecting these compounds. Thus, the objective of this work is to review the toxicological aspects, traditional use/therapeutic potential and the analytical methods developed in biological matrices in twelve plant specimens (Areca catechu, Argyreia nervosa, Ayahuasca, Catha edulis, Datura stramonium, Lophophora williamsii, Mandragora officinarum, Mitragyna speciosa, Piper methysticum Forst, Psilocybe, Salvia divinorum and Tabernanthe iboga).

The effects of chronic mitragynine (Kratom) exposure on the EEG in rats

Mitragynine is the main alkaloid isolated from the leaves of Mitragyna speciosa Korth (Kratom). Kratom has been widely used to relieve pain and opioid withdrawal symptoms in humans but may also cause memory deficits. Here we investigated the changes in brain electroencephalogram (EEG) activity after acute and chronic exposure to mitragynine in freely moving rats. Vehicle, morphine (5 mg/kg) or mitragynine (1, 5 and 10 mg/kg) were administered for 28 days, and EEG activity was repeatedly recorded from the frontal cortex, neocortex and hippocampus. Repeated exposure to mitragynine increased delta, but decreased alpha powers in both cortical regions. It further decreased delta power in the hippocampus. These findings suggest that acute and chronic mitragynine can have profound effects on EEG activity, which may underlie effects on behavioral activity and cognition, particularly learning and memory function.

Plants with Anti-Addictive Potential

Drug addiction is prevalent among individuals of modern society, being a major cause of disability and premature loss of life. Although the drug addiction have profound social, economical and health impact in the world population, its management remains a challenge as available pharmacological treatments remains ineffective for most people. The limited efficacy and adverse effects have led to a search for alternative therapies to treat drug addiction. In this context, natural products are an important source for new chemical substances with a potential therapeutic applicability. Therefore, this chapter will present data obtained after an extensive literature search regarding the use of medicinal plants as a pharmacological alternative for drug addiction treatment.

Cross-reinstatement of mitragynine and morphine place preference in rats

Kratom is a medicinal plant that exhibits promising results as an opiate substitute. However, there is little information regarding the abuse profile of its main psychoactive constituent, mitragynine (MG), particularly in relapse to drug abuse. Using the place conditioning procedure as a model of relapse, this study aims to evaluate the ability of MG to induce conditioned place preference (CPP) reinstatement in rats. To evaluate the cross-reinstatement effects, MG and morphine were injected to rats that previously extinguished a morphine- or MG-induced CPP. Following a CPP acquisition induced by either MG (10 and 30 mg/kg, i.p.) or morphine (10 mg/kg, i.p.), rats were subjected to repeated CPP extinction sessions. A low dose priming injection of MG or morphine produced a reinstatement of the previously extinguished CPP. In the second experiment of this study, a priming injection of morphine (1, 3 and 10 mg/kg, i.p.) dose-dependently reinstated an MG-induced CPP. Likewise, a priming injection of MG (3, 10 and 30 mg/kg, i.p.) was able to dose-dependently reinstate a morphine-induced CPP. The present study demonstrates a cross-reinstatement effect between MG and morphine, thereby suggesting a similar interaction in their rewarding motivational properties. The findings from this study also suggesting that a priming exposure to kratom and an opioid may cause relapse for a previously abused drug.

Evaluation of the rewarding effects of mitragynine and 7-hydroxymitragynine in an intracranial self-stimulation procedure in male and female rats

BACKGROUND

Kratom (Mitragyna speciosa Korth.) has been used in Southeast Asia for hundreds of years to increase energy, for relaxation, and to diminish opioid withdrawal. Kratom use has recently spread to Western countries. Kratom could potentially be used for the treatment of opioid withdrawal and pain, but more insight is needed into its abuse potential. Therefore, we investigated the rewarding properties of the primary kratom alkaloid mitragynine and its active metabolite 7-hydroxymitragynine, and morphine as a reference drug in male and female rats. These compounds have agonist activity at mu-opioid receptors.

METHODS

The compounds were tested in an intracranial self-stimulation (ICSS) procedure, which allows for the evaluation of the rewarding/aversive and sedative effects of drugs. Rewarding doses of drugs decrease the brain reward thresholds, and aversive drug doses have the opposite effect.

RESULTS

Mitragynine, 7-hydroxymitragynine, and morphine affected the brain reward thresholds. A high dose of 7-hydroxymitragynine (3.2 mg/kg) increased the brain reward thresholds, whereas an intermediate dose of morphine (10 mg/kg) decreased the reward thresholds. 7-Hydroxymitragynine and morphine affected the response latencies. Five mg/kg of morphine increased response latencies. 7-Hydroxymitragynine tended to increase the response latencies, but the post hoc analyses did not reveal a significant effect. There were no sex differences in the effects of mitragynine, 7-hydroxymitragynine, and morphine on the reward thresholds and the response latencies.

CONCLUSIONS

These initial findings indicate that mitragynine and 7-hydroxymitragynine are not rewarding in the ICSS procedure. The present results suggest that these kratom alkaloids do not have abuse potential.

Kratom instrumentalization for severe pain self-treatment resulting in addiction - A case report of acute and chronic subjective effects

Background

Kratom is a Southeast Asian plant, which is widely used in this region, and making an increasing appearance in Europe and the US.

Case report

We present the case of a 26-year-old man in Substitol-assisted treatment of excessive Kratom and Tilidin use expressing the wish for a drug-free management of a chronic pain condition. After an accidental calcaneus impression fracture, the patient was suffering from severe chronic pain and anxiety of further accidents. This was managed initially with Tilidin. Resulting from the wish to self-manage the pain condition in a way that permitted continuation of a job, the patient searched for a ‘natural’ treatment alternative obtained from an Internet vendor. He successfully instrumentalized Kratom for 3 years with daily consumption intermixed with occasional Tilidin for pain management. However, the dose of Kratom was increased considerably up to a level of effect reversal, when no analgesic and behaviorally activating effects occurred any more, but only intense drowsiness. The patient was treatment seeking and subsequently detoxified from Kratom and Tilidin. Pain management was shifted to retarded morphine.

Conclusion

Kratom instrumentalization for pain management might appear to be more problematic for addiction development than when its use is established for other consumption motives.

Acute mitragynine administration suppresses cortical oscillatory power and systems theta coherence in rats

BACKGROUND

Mitragynine is the major alkaloid of Mitragyna speciosa (kratom) with potential as a therapeutic in pain management and in depression. There has been debate over the potential side effects of the drug including addiction risk and cognitive decline.

AIMS

To evaluate the effects of mitragynine on neurophysiological systems function in the prefrontal cortex (PFC), cingulate cortex (Cg), orbitofrontal cortex, nucleus accumbens (NAc), hippocampus (HIP), thalamus (THAL), basolateral amygdala (BLA) and ventral tegmental area of rats.

METHODS

Local field potential recordings were taken from animals at baseline and for 45 min following mitragynine administration (10 mg/kg, intraperitoneally). Drug-induced changes in spectral power and coherence between regions at specific frequencies were evaluated. Mitragynine-induced changes in c-fos expression were also analyzed.

RESULTS

Mitragynine increased delta power and reduced theta power in all three cortical regions that were accompanied by increased c-fos expression. A transient suppression of gamma power in PFC and Cg was also evident. There were no effects of mitragynine on spectral power in any of the other regions. Mitragynine induced a widespread reduction in theta coherence (7-9 Hz) that involved disruptions in cortical and NAc connectivity with the BLA, HIP and THAL.

CONCLUSIONS

These findings show that mitragynine induces frequency-specific changes in cortical neural oscillatory activity that could potentially impact cognitive functioning. However, the absence of drug effects within regions of the mesolimbic pathway may suggest either a lack of addiction potential, or an underlying mechanism of addiction that is distinct from other opioid analgesic agents.

Assessing physiological dependence and withdrawal potential of mitragynine using schedule-controlled behaviour in rats

RATIONALE

Kratom is proposed to exhibit therapeutic potential as an opium substitute, but little is known about its dependence-producing profile, particularly of its main psychoactive compound, mitragynine (MG).

OBJECTIVES

This study examined the dependence-producing effects of MG using operant-scheduled behaviour in rats and investigated the potential therapeutic effect of MG by comparing effects to buprenorphine in morphine-dependent rats using the same schedule-controlled behavioural task.

METHODS

The effects of acutely administered MG and morphine were determined in rats trained to respond under fixed-ratio (FR) 10 schedule of food reinforcement. Next, the rats were administered MG and morphine twice daily for 14 consecutive days to determine if physiological dependence would develop by examining cessation of drug treatment and following antagonist-precipitated withdrawal. The study then examined the effects of MG substitution to suppress naloxone-precipitated morphine withdrawal effects on scheduled responding.

RESULTS

Acute doses of MG did not produce dose-related decreases on FR schedules of responding compared to morphine. Unlike morphine, MG-treated rats showed no suppression of response rates following cessation of MG treatment. However, withdrawal effects were evident for MG after precipitation by either naloxone or SR141716A (rimonabant), similar to morphine-treated rats. MG in higher doses (10 and 30 mg/kg) attenuated the naloxone-precipitated morphine withdrawal effects while smaller doses of buprenorphine (0.3 and 1.0 mg/kg) were necessary to alleviate these effects.

CONCLUSION

The findings suggest that MG does not induce physiological dependence but can alleviate the physical symptoms associated with morphine withdrawal which represent the desired characteristics of novel pharmacotherapeutic interventions for managing opioid use disorder (OUD).

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Mitragynine Attenuates Morphine Withdrawal Effects in Rats-A Comparison With Methadone and Buprenorphine

BACKGROUND

Opiate addiction is a major health problem in many countries. A crucial component of the medical treatment is the management of highly aversive opiate withdrawal signs, which may otherwise lead to resumption of drug taking. In a medication-assisted treatment (MAT), methadone and buprenorphine have been implemented as substitution drugs. Despite MAT effectiveness, there are still limitations and side effects of using methadone and buprenorphine. Thus, other alternative therapies with less side effects, overdosing, and co-morbidities are desired. One of the potential pharmacotherapies may involve kratom's major indole alkaloid, mitragynine, since kratom (Mitragyna speciosa Korth.) preparations have been reported to alleviate opiate withdrawal signs in self-treatment in Malaysian opiate addicts.

METHODS

Based on the morphine withdrawal model, rats were morphine treated with increasing doses from 10 to 50 mg/kg twice daily over a period of 6 days. The treatment was discontinued on day 7 in order to induce a spontaneous morphine abstinence. The withdrawal signs were measured daily after 24 h of the last morphine administration over a period of 28 abstinence days. In rats that developed withdrawal signs, a drug replacement treatment was given using mitragynine, methadone, or buprenorphine and the global withdrawal score was evaluated.

RESULTS

The morphine withdrawal model induced profound withdrawal signs for 16 days. Mitragynine (5-30 mg/kg; i.p.) was able to attenuate acute withdrawal signs in morphine dependent rats. On the other hand, smaller doses of methadone (0.5-2 mg/kg; i.p.) and buprenorphine (0.4-1.6 mg/kg; i.p.) were necessary to mitigate these effects.

CONCLUSIONS

These data suggest that mitragynine may be a potential drug candidate for opiate withdrawal treatment.

Pharmacokinetics and pharmacodynamics of mitragynine, the principle alkaloid of Mitragyna speciosa: present knowledge and future directions in perspective of pain

Mitragyna speciosa, commonly known as Ketum or Biak in Malaysia and Kratom in Thailand, is a native plant to Southeast Asia and has various pharmacological benefits. Mitragynine (MG) is the principal alkaloid found in the leaves of Mitragyna speciosa and has been reported to be responsible for the plant's therapeutic actions. Traditionally, local communities use Kratom preparations for relief from different types of pain. The potential analgesic effects of MG using rodent models have been reported in literatures. We have reviewed the published analgesic and pharmacokinetic studies and all of these findings showed the routes of drug administration, doses employed, and type of vehicles used to solubilize the drug, varied considerably; hence this posted difficulties in predicting the drug's pharmacokinetic-response relationship. A rational approach is warranted for accurate prediction of dose-response relationship; as this is essential for the development of MG as an alternative medicinal drug for pain management. PKPD modeling would serve as a better method to understand the dose-response relationship in future MG preclinical and clinical studies.

Rate and extent of mitragynine and 7-hydroxymitragynine blood-brain barrier transport and their intra-brain distribution: the missing link in pharmacodynamic studies

Mitragyna speciosa is reported to be beneficial for the management of chronic pain and opioid withdrawal in the evolving opioid epidemic. Data on the blood-brain barrier (BBB) transport of mitragynine and 7-hydroxymitragynine, the active compounds of the plant, are still lacking and inconclusive. Here, we present for the first time the rate and the extent of mitragynine and 7-hydroxymitragynine transport across the BBB, with an investigation of their post-BBB intra-brain distribution. We utilized an in vitro BBB model to study the rate of BBB permeation of the compounds and their interaction with efflux transporter P-glycoprotein (P-gp). Mitragynine showed higher apical-to-basolateral (A-B, i.e. blood-to-brain side) permeability than 7-hydroxymitragynine. 7-Hydroxymitragynine showed a tendency to efflux, with efflux ratio (B-A/A-B) of 1.39. Both were found to inhibit the P-gp and are also subject to efflux by the P-gp. Assessment of the extent of BBB transport in vivo in rats from unbound brain to plasma concentration ratios (K_p,uu,brain ) revealed extensive efflux of both compounds, with less than 10 percent of unbound mitragynine and 7-hydroxymitragynine in plasma crossing the BBB. By contrast, the extent of intra-brain distribution was significantly different, with mitragynine having 18-fold higher brain tissue uptake in brain slice assay compared with 7-hydroxymitragynine. Mitragynine showed a moderate capacity to accumulate inside brain parenchymal cells, while 7-hydroxymitragynine showed restricted cellular barrier transport. The presented findings from this systematic investigation of brain pharmacokinetics of mitragynine and 7-hydroxymitragynine are essential for design and interpretation of in vivo experiments aiming to establish exposure-response relationship.

Abuse liability and therapeutic potential of the Mitragyna speciosa (kratom) alkaloids mitragynine and 7-hydroxymitragynine

Kratom, derived from the plant Mitragyna speciosa, is receiving increased attention as an alternative to traditional opiates and as a replacement therapy for opiate dependence. Mitragynine (MG) and 7-hydroxymitragynine (7-HMG) are major psychoactive constituents of kratom. While MG and 7-HMG share behavioral and analgesic properties with morphine, their reinforcing effects have not been examined to date. 7-HMG, but not MG, substituted for morphine self-administration in a dose-dependent manner in the rat self-administration paradigm. Following the substitution procedure, re-assessment of morphine self-administration revealed a significant increase following 7-HMG and a significant decrease following MG substitution. In a separate cohort, 7-HMG, but not MG, engendered and maintained intravenous self-administration in a dose-dependent manner. The effects of pretreatment with nalxonaxine (NLXZ), a μ1 opiate receptor antagonist, and naltrindole (NTI), a δ opiate receptor antagonist, on 7-HMG and morphine self-administration were also examined. Both NLXZ and NTI reduced 7-HMG self-administration, whereas only NLXZ decreased morphine intake. The present results are the first to demonstrate that 7-HMG is readily self-administered, and the reinforcing effects of 7-HMG are mediated in part by μ and δ opiate receptors. In addition, prior exposure to 7-HMG increased subsequent morphine intake whereas prior exposure to MG decreased morphine intake. The present findings indicate that MG does not have abuse potential and reduces morphine intake, desired characteristics of candidate pharmacotherapies for opiate addiction and withdrawal, whereas 7-HMG should be considered a kratom constituent with high abuse potential that may also increase the intake of other opiates.

Substance Use Disorder Related to Kratom (Mitragyna speciosa) Use in Malaysia

Background:

Kratom is a traditional medicinal herb with mild addictive properties. Nevertheless, current available data on substance use disorder related to kratom use is scarce. This study aims to clinically evaluate and identify factors that are associated with kratom use disorder among regular kratom tea/juice users in traditional settings in Malaysia. </P><P> Method: 150 regular kratom users were recruited through convenient sampling for this crosssectional study. They were interviewed with Mini International Neuropsychiatric Interview (M.I.N.I.) to diagnose substance use disorder related to kratom use, while the Ketum Dependence Scale (KDS) and Clinical Opioid Withdrawal Scale (COWS) were administered to evaluate kratom dependence and withdrawal severity.

Results:

All subjects were males with the majority being Malays (99%, n=148/150). More than half were single (n=84/150), had secondary education (91%, n=136/150), and were employed (93%, n=139/150). Almost all (99%) fulfilled the criteria for substance use disorder related to kratom use, 95% reported withdrawal symptoms on abstinence, 87% reported tolerance, and 93% craving for kratom. Results from Chi-square analysis indicated that higher quantity (>3 glasses) of daily kratom tea/juice consumption was significantly associated with severe kratom dependence (OR: 2.1: 1.0-4.5: p<.041) and moderate withdrawal (OR: 3.1: 1.5-6.3: p<.002). Similarly, those who consumed >3 glasses of brewed kratom tea daily had higher odds of reporting longer kratom use history (>7 years) (OR: 4.4: 2.2-8.8: p<.001) and higher frequency of daily kratom use (>5 times) (p<.001), compared to those who consumed less than three glasses of kratom daily.

Conclusion:

Our findings indicated that regular and chronic (>3 glasses daily) kratom tea/juice consumption was associated with kratom use disorder, severe kratom dependence and moderate withdrawal.

Long-Term Cognitive Effects of Kratom (Mitragyna speciosa Korth.) Use

Kratom or Mitragyna speciosa (Korth.) is a medicinal plant of Southeast Asia. As a result of its opioid-like effects, it remains unknown whether consumption of kratom tea is associated with impaired cognitive function. We assessed the cognitive function of 70 regular kratom users and 25 control participants using the Cambridge Neuropsychological Test Automated Battery. Participants performed six neuropsychological tasks that assessed motor, learning and memory, attention and executive function. Relative to control participants, higher consumption (>3 glasses daily or mitragynine doses between 72.5 mg and 74.9 mg) of kratom tea was selectively associated with impaired performance on the Paired Associates Learning task, reflecting deficits in visual episodic memory and new learning. Overall, the performance of kratom users compared to control participants, and the performance of high (>3 glasses per day) as well as low (≤3 glasses per day) kratom using groups, were comparable on all neuropsychological domains. Higher intake of kratom juice (>3 glasses daily) did not appear to impair motor, memory, attention or executive function of regular kratom users.

Abuse liability of mitragynine assessed with a self-administration procedure in rats

RATIONALE

Substantial use of the plant kratom for psychoactive effects has driven interest in its abuse liability. Several place conditioning studies suggest abuse liability of the active ingredient mitragynine, though studies of its self-administration have not been published.

METHODS

Binding of mitragynine to rat brain mu, kappa, and delta opioid receptors was compared to that for heroin and morphine. Self-administration of mitragynine, heroin, methamphetamine, or saline was assessed during single-session substitutions in rats trained to self-administer methamphetamine (0.022 mg/kg/injection, i.v.) during 1-h daily sessions.

RESULTS

Mitragynine had > 2- or ~ 16-fold greater affinity for the mu opioid receptor than, respectively, for kappa or delta opioid receptors. Its affinity for the mu receptor was ~ 200-fold less than that for morphine. In rats trained to self-administer methamphetamine, saline substitutions significantly decreased the number of responses, whereas different doses of methamphetamine (0.002-0.068 mg/kg/injection) or heroin (0.001-0.03 mg/kg/injection) maintained self-administration with maximal responding at 0.022 or 0.01 mg/kg/injection, respectively. In contrast, no dose of mitragynine maintained response rates greater than those obtained with saline. Presession mitragynine treatment (0.1 to 3.0 mg/kg) decreased response rates maintained by heroin but had little effect on responding maintained by methamphetamine across the same range of doses.

CONCLUSIONS

These results suggest a limited abuse liability of mitragynine and potential for mitragynine treatment to specifically reduce opioid abuse. With the current prevalence of opioid abuse and misuse, it appears currently that mitragynine is deserving of more extensive exploration for its development or that of an analog as a medical treatment for opioid abuse.

Prevalence and motivations for kratom use in a sample of substance users enrolled in a residential treatment program

BACKGROUND

Kratom use in the West has increased recently, yet the prevalence and motives for use among individuals with a history of substance use disorder (SUD) have not been fully examined. Kratom has been documented as a means of treating chronic pain, mitigating drug dependence, and easing withdrawal symptoms, yet it is unclear if substance users are utilizing kratom as a self-medication. Abuse liability, side effects, and overall appeal of kratom remain uncertain.

METHODS

In April 2017, an anonymous survey regarding kratom use and motivations was completed by clients enrolled in a 12-Step-oriented residential program. 500 respondents with a self-reported history of SUD completed the survey.

RESULTS

20.8% of respondents endorsed lifetime kratom use and 10.2% reported past-12-month use. Kratom-users were younger (=32.1 vs. 35.9, p<0.001) and were more versatile substance users. A majority (68.9%) of kratom-users reported having used the drug as a means of reducing or abstaining from non-prescription opioids (NPO) and/or heroin, and 64.1% reported using kratom as a substitute for NPO/heroin. 18.4% of kratom-users reported using the drug due to a disability or chronic pain. One-third of kratom-users stated that kratom was a helpful substance and that they would try it again. However, kratom was not preferred and was indicated as having less appeal than NPO, heroin, amphetamines, and Suboxone.

CONCLUSIONS

Among substance users, kratom use may be initiated for a variety of reasons, including as a novel form of harm-reduction or drug substitution, particularly in the context of dependence and withdrawal from other substances.

The medicinal chemistry and neuropharmacology of kratom: A preliminary discussion of a promising medicinal plant and analysis of its potential for abuse

The leaves of Mitragyna speciosa (commonly known as kratom), a tree endogenous to parts of Southeast Asia, have been used traditionally for their stimulant, mood-elevating, and analgesic effects and have recently attracted significant attention due to increased use in Western cultures as an alternative medicine. The plant's active alkaloid constituents, mitragynine and 7-hydroxymitragynine, have been shown to modulate opioid receptors, acting as partial agonists at mu-opioid receptors and competitive antagonists at kappa- and delta-opioid receptors. Furthermore, both alkaloids are G protein-biased agonists of the mu-opioid receptor and therefore, may induce less respiratory depression than classical opioid agonists. The Mitragyna alkaloids also appear to exert diverse activities at other brain receptors (including adrenergic, serotonergic, and dopaminergic receptors), which may explain the complex pharmacological profile of raw kratom extracts, although characterization of effects at these other targets remains extremely limited. Through allometric scaling, doses of pure mitragynine and 7-hydroxymitragynine used in animal studies can be related to single doses of raw kratom plant commonly consumed by humans, permitting preliminary interpretation of expected behavioral and physiological effects in man based on this preclinical data and comparison to both anecdotal human experience and multiple epidemiological surveys. Kratom exposure alone has not been causally associated with human fatalities to date. However, further research is needed to clarify the complex mechanism of action of the Mitragyna alkaloids and unlock their full therapeutic potential. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Novel Psychoactive Substances-Recent Progress on Neuropharmacological Mechanisms of Action for Selected Drugs

A feature of human culture is that we can learn to consume chemical compounds, derived from natural plants or synthetic fabrication, for their psychoactive effects. These drugs change the mental state and/or the behavioral performance of an individual and can be instrumentalized for various purposes. After the emergence of a novel psychoactive substance (NPS) and a period of experimental consumption, personal and medical benefits and harm potential of the NPS can be estimated on evidence base. This may lead to a legal classification of the NPS, which may range from limited medical use, controlled availability up to a complete ban of the drug form publically accepted use. With these measures, however, a drug does not disappear, but frequently continues to be used, which eventually allows an even better estimate of the drug's properties. Thus, only in rare cases, there is a final verdict that is no more questioned. Instead, the view on a drug can change from tolerable to harmful but may also involve the new establishment of a desired medical application to a previously harmful drug. Here, we provide a summary review on a number of NPS for which the neuropharmacological evaluation has made important progress in recent years. They include mitragynine ("Kratom"), synthetic cannabinoids (e.g., "Spice"), dimethyltryptamine and novel serotonergic hallucinogens, the cathinones mephedrone and methylone, ketamine and novel dissociative drugs, γ-hydroxybutyrate, γ-butyrolactone, and 1,4-butanediol. This review shows not only emerging harm potentials but also some potential medical applications.