Clinical Pharmacokinetic Assessment of Kratom (Mitragyna speciosa), a Botanical Product with Opioid-like Effects, in Healthy Adult Participants

Kratom addiction per DSM-5 SUD criteria, and kratom physical dependence: Insights from dosing amount versus frequency

BACKGROUND

Kratom products are widely used in the United States, with inadequate understanding of how dosing amounts/frequencies relate to outcomes.

METHODS

Between July-November 2022, we enrolled 395 active US adult kratom consumers into a remote study with a baseline survey. We examined self-reported typical dose amounts and frequencies across people and product types, and their associations with outcomes: multiple regression was used to examine whether amounts and frequencies (doses/day) were associated with acute effects, withdrawal symptoms, scores on the Subjective Opioid Withdrawal Scale (SOWS), and addiction (operationalized as DSM-5-based symptoms of kratom-use disorder, KUD).

RESULTS

Participants were 54.9% male, aged 38.1 on average, and 81.3% White. Mean length of kratom use was 5.7 years. Most (95.9%) reported regularly using whole-leaf kratom products; 16 (4.1%) reported regular extract use. SOWS scores were mild to moderate on average (13.5, SD 11.9). KUD symptom counts were mostly in the mild/moderate range (80.7%). Withdrawal and KUD symptoms were more closely associated with dose frequency than dose amount. Men reported more acute effects, withdrawal symptoms with cessation, and KUD symptoms than women.

CONCLUSIONS

Greater dose amount and frequency were systematically related to the number of withdrawal symptoms upon cessation and to KUD symptoms; the relationship was stronger for dose frequency than amount. Men may have more acute effects and more withdrawal and KUD symptoms than women. Although kratom may be used nonproblematically by some consumers, physical dependence (tolerance, withdrawal, or use to avoid withdrawal) and KUD become more likely with increasing dose frequency.

Discovery of procyanidin condensed tannins of (-)-epicatechin from Kratom, Mitragyna speciosa, as virucidal agents against SARS-CoV-2

Kratom, Mitragyna speciosa, is one of the most popular herbs in the West and Southeast Asia. A number of previous works have focused on bioactive alkaloids in this plant; however, non-alkaloids have never been investigated for their biological activities. Antiviral and virucidal assays of a methanol leaf extract of Kratom, M. speciosa, revealed that a crude extract displayed virucidal activity against the SARS-CoV-2. Activity-guided isolation of a methanol leaf extract of Kratom led to the identification of B-type procyanidin condensed tannins of (-)-epicatechin as virucidal compounds against SARS-CoV-2. The fraction containing condensed tannins exhibited virucidal activity with an EC50 value of 8.38 μg/mL and a selectivity index (SI) value >23.86. LC-MS/MS analysis and MALDI-TOF MS identified the structure of the virucidal compounds in Kratom as B-type procyanidin condensed tannins, while gel permeation chromatograph (GPC) revealed weight average molecular weight of 238,946 Da for high molecular-weight condensed tannins. In addition to alkaloids, (-)-epicatechin was found as a major component in the leaves of M. speciosa, but it did not have virucidal activity. Macromolecules of (-)-epicatechin, i.e., procyanidin condensed tannins, showed potent virucidal activity against SARS-CoV-2, suggesting that the high molecular weights of these polyphenols are important for virucidal activity.

Research and publication gaps on kratom and kratom products: a scoping review of current literature

PURPOSE OF REVIEW

Kratom plant, products derived from the plant, and plant phytochemicals are of great interest among researchers, clinicians, and consumers. However, there is a paucity of rigorously collected scientific data on their risk/safety profile and public health impact. This scoping review discusses original research articles published between 2022 and 2023. It focuses on identifying publication gaps on topics related to epidemiology, public health, and risk/safety profiles comparing evidence collected by researchers from Southeast Asia and the West.

RECENT FINDINGS

Our review of the Scopus database identified a total of 55 publications, including clinical case reports and case series reports, surveys, studies enrolling human participants, and publications based on large-scale national surveys or large-scale national or international health system database records.

SUMMARY

Overall, there is dearth of reliable data on key epidemiological factors, including the prevalence rates, and on objective and reliable indices of the risk/safety profiles. Rigorous and systematic studies including improved epidemiological surveillance, human laboratory, and controlled clinical studies are urgently needed to advance our understanding of public health consequences of consuming kratom and kratom-derived products and to improve our understanding of their risk/safety profile and additional analytical studies to better inform development of needed regulatory oversight.

Kratom safety and toxicology in the public health context: research needs to better inform regulation

Although kratom use has been part of life for centuries in Southeast Asia, the availability and use of kratom in the United States (US) increased substantially since the early 2000s when there was little information on kratom pharmacology, use patterns, and effects, all critical to guiding regulation and policy. Here we provide a synthesis of research with several hundred English-language papers published in the past 5 years drawing from basic research, epidemiological and surveillance data, and recent clinical research. This review of available literature aims to provide an integrated update regarding our current understanding of kratom's benefits, risks, pharmacology, and epidemiology, which may inform United States-based kratom regulation. Recent surveillance indicates there are likely several million past-year kratom consumers, though estimates vary widely. Even without precise prevalence data, kratom use is no longer a niche, with millions of United States adults using it for myriad reasons. Despite its botanical origins in the coffee tree family and its polypharmacy, kratom is popularly characterized as an opioid with presumed opioid-system-based risks for addiction or overdose. Neuropharmacology, toxicology, and epidemiology studies show that kratom is more accurately characterized as a substance with diverse and complex pharmacology. Taken together the work reviewed here provides a foundation for future scientific studies, as well as a guide for ongoing efforts to regulate kratom. This work also informs much-needed federal oversight, including by the United States Food and Drug Administration. We conclude with recommendations for kratom regulation and research priorities needed to address current policy and knowledge gaps around this increasingly used botanical product.

Effects of kratom on driving: Results from a cross-sectional survey, ecological momentary assessment, and pilot simulated driving Study

OBJECTIVES

Despite widespread kratom use, there is a lack of knowledge regarding its effects on driving. We evaluated the self-reported driving behaviors of kratom consumers and assessed their simulated-driving performance after self-administering kratom products.

METHODS

We present results from: 1) a remote, national study of US adults who regularly use kratom, and 2) an in-person substudy from which we re-recruited participants. In the national study (N = 357), participants completed a detailed survey and a 15-day ecological momentary assessment (EMA) that monitored naturalistic kratom use. For the remote study, outcomes were self-reported general and risky driving behaviors, perceived impairment, and driving confidence following kratom administration. For the in-person substudy, 10 adults consumed their typical kratom products and their driving performance on a high-fidelity driving simulator pre- and post-kratom administration was evaluated.

RESULTS

Over 90% of participants surveyed self-reported driving under the influence of kratom. Most reported low rates of risky driving behavior and expressed high confidence in their driving ability after taking kratom. This was consistent with EMA findings: participants reported feeling confident in their driving ability and perceived little impairment within 15-180 min after using kratom. In the in-person substudy, there were no significant changes in simulated driving performance after taking kratom.

CONCLUSIONS

Using kratom before driving appears routine, however, self-reported and simulated driving findings suggest kratom effects at self-selected doses among regular kratom consumers do not produce significant changes in subjective and objective measures of driving impairment. Research is needed to objectively characterize kratom's impact on driving in regular and infrequent consumers.

Responses to a "Typical" Morning Dose of Kratom in People Who Use Kratom Regularly: A Direct-Observation Study

INTRODUCTION

Use of kratom has outpaced systematic study of its effects, with most studies reliant on retrospective self-report.

METHODS

We aimed to assess acute effects following kratom use in adults who use regularly, and quantify alkaloids in the products, urine, and plasma. Between July and November 2022, 10 adults came to our clinic and orally self-administered their typical kratom dose; blinding procedures were not used. Physiological measures included blood pressure, respiratory rate, heart rate, pulse oximetry, temperature, and pupil diameter. Subjective outcomes included Subjective Opioid Withdrawal Scale, Addiction Research Center Inventory, and Drug Effects Questionnaire. Psychomotor performance was also assessed.

RESULTS

Participants were 6 men and 4 women, mean age 41.2 years. Nine were non-Hispanic White; 1 was biracial. They had used kratom for 6.6 years (SD, 3.8 years) on average (2.0-14.1). Sessions were 190.89 minutes on average (SD, 15.10 minutes). Mean session dose was 5.16 g (median, 4.38 g; range, 1.1-10.9 g) leaf powder. Relative to baseline, physiological changes were minor. However, pupil diameter decreased (right, b = -0.70, P < 0.01; left, b = -0.73, P < 0.01) 40-80 minutes postdose and remained below baseline >160 minutes. Subjective Opioid Withdrawal Scale pre-dosing was mild (5.5 ± 3.3) and decreased postdose (b = [-4.0, -2.9], P < 0.01). Drug Effects Questionnaire "feeling effects" increased to 40/100 (SD, 30.5) within 40 minutes and remained above baseline 80 to 120 minutes (b = 19.0, P = 0.04), peaking at 72.7/100; 6 participants rated euphoria as mild on the Addiction Research Center Inventory Morphine-Benzedrine-scale. Psychomotor performance did not reliably improve or deteriorate postdosing.

CONCLUSIONS

Among regular consumers, we found few clinically significant differences pre- and post-kratom dosing. Alkaloidal contents in products were within expected ranges.

Human Mitragynine and 7-Hydroxymitragynine Pharmacokinetics after Single and Multiple Daily Doses of Oral Encapsulated Dried Kratom Leaf Powder

Kratom leaves, consumed by millions worldwide as tea or ground leaf powder, contain multiple alkaloids, with mitragynine being the most abundant and responsible for most effects. Mitragynine is a partial µ-opioid receptor agonist and competitive antagonist at κ- and δ-opioid receptors; however, unlike morphine, it does not activate the β-arrestin-2 respiratory depression pathway. Due to few human mitragynine data, the largest randomized, between-subject, double-blind, placebo-controlled, dose-escalation study of 500-4000 mg dried kratom leaf powder (6.65-53.2 mg mitragynine) was conducted. LC-MS/MS mitragynine and 7-hydroxymitragynine plasma concentrations were obtained after single and 15 daily doses. Mitragynine and 7-hydroxymitragynine Cmax increased dose proportionally, and AUC was slightly more than dose proportional. The median mitragynine Tmax was 1.0-1.3 h after single and 1.0-1.7 h after multiple doses; for 7-hydroxymitragynine Tmax, it was 1.2-1.8 h and 1.3-2.0 h. Steady-state mitragynine concentrations were reached in 8-9 days and 7-hydroxymitragynine within 7 days. The highest mean mitragynine T1/2 was 43.4 h after one and 67.9 h after multiple doses, and, for 7-hydroxymitragynine, it was 4.7 and 24.7 h. The mean 7-hydroxy-mitragynine/mitragynine concentration ratios were 0.20-0.31 after a single dose and decreased (0.15-0.21) after multiple doses. These mitragynine and 7-hydroxymitragynine data provide guidance for future clinical kratom dosing studies and an interpretation of clinical and forensic mitragynine and 7-hydroxymitragynine concentrations.

An update on the clinical pharmacology of kratom: uses, abuse potential, and future considerations

INTRODUCTION

Kratom (Mitragyna speciosa) has generated substantial clinical and scientific interest as a complex natural product. Its predominant alkaloid mitragynine and several stereoisomers have been studied for activity in opioid, adrenergic, and serotonin receptors. While awaiting clinical trial results, the pre-clinical evidence suggests a range of potential therapeutic applications for kratom with careful consideration of potential adverse effects.

AREAS COVERED

The focus of this review is on the pharmacology, pharmacokinetics, and potential drug-drug interactions of kratom and its individual alkaloids. A discussion on the clinical pharmacology and toxicology of kratom is followed by a summary of user surveys and the evolving concepts of tolerance, dependence, and withdrawal associated with kratom use disorder.

EXPERT OPINION

With the increasing use of kratom in clinical practice, clinicians should be aware of the potential benefits and adverse effects associated with kratom. While many patients may benefit from kratom use with few or no reported adverse effects, escalating dose and increased use frequency raise the risk for toxic events in the setting of polysubstance use or development of a use disorder.

An in vitro evaluation of kratom (Mitragyna speciosa) on the catalytic activity of carboxylesterase 1 (CES1)

Kratom, (Mitragyna Speciosa Korth.) is a plant indigenous to Southeast Asia whose leaves are cultivated for a variety of medicinal purposes and mostly consumed as powders or tea in the United States. Kratom use has surged in popularity with the lay public and is currently being investigated for possible therapeutic benefits including as a treatment for opioid withdrawal due to the pharmacologic effects of its indole alkaloids. A wide array of psychoactive compounds are found in kratom, with mitragynine being the most abundant alkaloid. The drug-drug interaction (DDI) potential of mitragynine and related alkaloids have been evaluated for effects on the major cytochrome P450s (CYPs) via in vitro assays and limited clinical investigations. However, no thorough assessment of their potential to inhibit the major hepatic hydrolase, carboxylesterase 1 (CES1), exists. The purpose of this study was to evaluate the in vitro inhibitory potential of kratom extracts and its individual major alkaloids using an established CES1 assay and incubation system. Three separate kratom extracts and the major kratom alkaloids mitragynine, speciogynine, speciociliatine, paynantheine, and corynantheidine displayed a concentration-dependent reversible inhibition of CES1. The experimental Ki values were determined as follows for mitragynine, speciociliatine, paynantheine, and corynantheidine: 20.6, 8.6, 26.1, and 12.5 μM respectively. Speciociliatine, paynantheine, and corynantheidine were all determined to be mixed-type reversible inhibitors of CES1, while mitragynine was a purely competitive inhibitor. Based on available pharmacokinetic data, determined Ki values, and a physiologically based inhibition screen mimicking alkaloid exposures in humans, a DDI mediated via CES1 inhibition appears unlikely across a spectrum of doses (i.e., 2-20g per dose). However, further clinical studies need to be conducted to exclude the possibility of a DDI at higher and extreme doses of kratom and those who are chronic users.

Evaluation of toxicity profile of kratom (Mitragyna speciosa Korth) decoction in rats

Mitragyna speciosa Korth also known as kratom, is an herbal drug preparation for its therapeutic properties and opioid-replacement therapy. Kratom is consumed in a brewed decoction form in Malaysia and to date, no studies have characterized its chemical and toxicity profile. Thus, this study aims to evaluate kratom decoction's safety and toxicity profile after 28 days of treatment. Mitragynine content was quantified in kratom decoction and used as a marker to determine the concentration. Male and female Sprague Dawley rats were orally treated with vehicle or kratom decoction (10, 50 or 150 mg/kg) and two satellite groups were treated with vehicle and kratom decoction (150 mg/kg). Blood and organs were collected for hematology, biochemical and histopathology analysis at the end of treatment. No mortality was found after 28 days of treatment and no significant changes in body weight and hematology profile, except for low platelet count. High amounts of uric acid, AST, ALT and alkaline phosphatase were found in the biochemical analysis. Histological investigation of the heart and lungs detected no alterations except for the kidney, liver and brain tissues. In conclusion, repeated administration of kratom decoction provided some evidence of toxicity in the kidney and liver with no occurrence of mortality.

Examining the Psychoactive Differences between Kratom Strains

Kratom (Mitragyna speciosa) is a Southeast Asian plant containing various alkaloids that induce pharmacological effects in humans. In Western countries, online vendors sell a variety of different kratom strains which are marketed to have distinct effect profiles. However, as of yet such marketing claims are unsubstantiated, and therefore the current study investigated whether differently colored kratom products can induce distinct effects, as self-reported by users. Six hundred forty-four current kratom users were anonymously surveyed to compare the self-reported effects of and motivations for using kratom products sold as red, green, and white strains. Most of the survey respondents were customers of the same kratom vendor, the products of which had been analyzed for their alkaloid content by an independent laboratory. The survey respondents reported distinct subjective experiences for different kratom strains, in a manner congruent with common marketing descriptions. However, the product analyses revealed no significant cross-strain differences in alkaloid content, suggesting that the reported effect differences might be disproportionally influenced by marketing narratives and anecdotal reports. Future studies should engage a more diverse population and include kratom strains from various vendors. Controlled, blinded experiments could assess whether the reported effect differences stem from a placebo effect or from alternative factors, e.g., minor alkaloids and terpenes.

Ventricular Arrhythmias Associated With Over-the-Counter and Recreational Opioids

BACKGROUND

Epidemic increases in opioid deaths prompted policies limiting access to prescription opioids in North America. Consequently, the over-the-counter opioids loperamide (Imodium A-D) and mitragynine, the herbal ingredient in kratom, are increasingly used to avert withdrawal or induce euphoria. Arrhythmia events related to these nonscheduled drugs have not been systematically studied.

OBJECTIVES

In this study, we sought to explore opioid-associated arrhythmia reporting in North America.

METHODS

The U.S. Food and Drug Administration Adverse Event Reporting System (FAERS), Center for Food Safety and Applied Nutrition Adverse Event Reporting System (CAERS), and Canada Vigilance Adverse Reaction (CVAR) databases were searched (2015-2021). Reports involving nonprescription drugs (loperamide, mitragynine) and diphenoxylate/atropine (Lomotil) were identified. Methadone, a prescription opioid (full agonist), served as a positive control owing to its established arrhythmia risk. Buprenorphine (partial agonist) and naltrexone (pure antagonist), served as negative controls. Reports were classified according to Medical Dictionary for Regulatory Activities terminology. Significant disproportionate reporting required a proportional reporting ratio (PRR) of ≥2, ≥3 cases, and chi-square ≥4. Primary analysis used FAERS data, whereas CAERS and CVAR data were confirmatory.

RESULTS

Methadone was disproportionately associated with ventricular arrhythmia reports (PRR: 6.6; 95% CI: 6.2-7.0; n = 1,163; chi-square = 5,456), including 852 (73%) fatalities. Loperamide was also significantly associated with arrhythmia (PRR: 3.2; 95% CI: 3.0-3.4; n = 1,008; chi-square = 1,537), including 371 (37%) deaths. Mitragynine demonstrated the highest signal (PRR: 8.9; 95% CI: 6.7-11.7; n = 46; chi-square = 315), with 42 (91%) deaths. Buprenorphine, diphenoxylate, and naltrexone were not associated with arrhythmia. Signals were similar in CVAR and CAERS.

CONCLUSIONS

The nonprescription drugs loperamide and mitragynine are associated with disproportionate reports of life-threatening ventricular arrhythmia in North America.

Kratom: The analytical challenge of an emerging herbal drug

Mitragyna speciosa or kratom is emerging worldwide as a "legal" herbal drug of abuse. An increasing number of papers is appearing in the scientific literature regarding its pharmacological profile and the analysis of its chemical constituents, mainly represented by alkaloids. However, its detection and identification are not straightforward as the plant material is not particularly distinctive. Hyphenated techniques are generally preferred for the identification and quantification of these compounds, especially the main purported psychoactive substances, mitragynine (MG) and 7-hydroxymitragynine (7-OH-MG), in raw and commercial products. Considering the vast popularity of this recreational drug and the growing concern about its safety, the analysis of alkaloids in biological specimens is also of great importance for forensic and toxicological laboratories. The review addresses the analytical aspects of kratom spanning the extraction techniques used to isolate the alkaloids, the qualitative and quantitative analytical methods and the strategies for the distinction of the naturally occurring isomers.

Clinical Implications of Kratom (Mitragyna speciosa) Use: a Literature Review

Purpose of Review

This work aims to provide an up-to-date review of the preclinical and clinical scientific literature on the therapeutic value of kratom to better understand the underlying mechanisms related to its use and inform future therapeutic applications.

Recent Findings

A growing number of studies, mainly of cross-sectional nature, describe the widespread use of kratom by individuals to self-treat pain, psychiatric symptoms, and substance use disorders (SUD) outside a controlled clinical setting. Preclinical evidence suggests kratom is effective as an analgesic agent and might decrease the self-administration of other drugs. A randomized controlled trial has further supported kratom's therapeutic value as an analgesic. Investigations in nonclinical samples of long-term kratom users also indicate its therapeutic benefit in managing SUD symptoms (e.g., craving) and long-term or acute symptoms (e.g., withdrawal) for alcohol, opioids, and other illicit drugs. However, episodes of kratom-related intoxications have also been reported, often due to the adulteration and the contamination of kratom products mainly sold online or mixed toxicities when consumed outside clinical and traditional settings.

Summary

Evidence on the clinical implications of kratom use is still limited and uncertain, with kratom research constantly evolving. Therefore, further randomized trials are needed.

Examining the paradoxical effects of kratom: a narrative inquiry

Introduction: Surveys and case reports have documented kratom use in the United States (US) for over a decade. However, those reports have generally not examined in depth the role kratom plays in the lives of those who use it regularly for sustained periods. Until there are controlled studies of the pharmacology and subjective effects of kratom alkaloids in humans, one of the best sources of insight on kratom-product use remains qualitative data with nuanced descriptions of kratom effects from those who use it regularly. Method: We conducted semistructured qualitative interviews with adults who regularly use kratom products, as part of a laboratory study of kratom-product self-administration. This qualitative component of the study was conducted as a narrative case-report series (n = 10). Results: Despite some differences among participants, all experienced acute combination effects that were largely, even simultaneously, analgesic and stimulatory. Most participants had decreased their dosages over time, and one planned to quit. Five of the 10 participants met DSM-5-based criteria for kratom-use disorder (3 mild, 1 moderate, 1 severe, by symptoms counts). When kratom was inadvertently taken in larger than intended doses, participants described a constellation of symptoms that they called "the wobbles" (a jittery feeling accompanied by what seemed to be nystagmus); this was rare, but could be of scientific and clinical interest as a possible manifestation of serotonin syndrome. Most participants described tolerance but considered kratom generally safe at low-moderate doses, providing perceived benefits with less potential risk for adverse effects compared to pharmaceuticals or illicit drugs. Discussion: In-depth interview data like these help confirm and clarify findings from larger survey studies and clinician-driven case reports. They are needed to inform the policy practice regarding kratom and may also help inform future experimental designs.

Kratom's Emergence and Persistence Within the US Polydrug Epidemic

Purpose of Review

Use of "kratom" products, derived from the bioactive botanical Mitragyna speciosa have increased amidst US polydrug use epidemics. Kratom alkaloids interact with opioid, serotonergic, adrenergic, and other receptors and regular users have described experiencing a wide range of effects. Some with polydrug use histories have reported using kratom as a substitute for other drugs or to nonmedically self-manage substance use disorder (SUD) symptoms. Data describing this remain scare and come from self-report. We review this literature describing kratom use as a drug substitute, or as a nonmedical "self-treatment" for attenuating dependence or SUD symptoms.

Recent Findings

Kratom products have been documented as being used as a licit and illicit opioid substitute. Use to reduce alcohol or stimulant consumption is less well documented. Although prior and current polydrug use appear common among a some kratom users, it is unclear if co-use is contemporaneous or concomitant. Temporal order of use initiation is typically undocumented. Use for energy and recreation are also increasingly reported.

Summary

Data on kratom consumption come primarily from self-report with significant limitations. Until controlled human laboratory studies have been conducted, we can presently only describe what is known about human kratom use based on self-report. Such data describe real-world kratom use, leaving unaddressed human abuse liability or therapeutic potential of kratom alkaloids. Clinicians should be mindful of use motivations among people with SUD histories, sensitively assessing use. The paucity of data highlights the urgent need to increase funding and research for understanding kratom's effects in humans.

Mitragyna speciosa (Kratom) poisoning: Findings from ten cases

Kratom is a mixture of compounds that are present in the leaves of the tropical tree Mitragyna speciosa. It is used as a psychoactive agent with both opiate and stimulant-like effects. In this case series we describe the signs, symptoms, and the management of kratom overdose in the prehospital setting and in intensive care. We retrospectively searched for cases in the Czech Republic. Over 36 months we found 10 cases of kratom poisoning, which healthcare records were analyzed and reported as per CARE guidelines. The dominant symptoms in our series were neurological and included quantitative (n = 9) or qualitative (n = 4) disorder of consciousness. Signs and symptoms of vegetative instability [hypertension (n = 3) and tachycardia (n = 3) vs. bradycardia/cardiac arrest (n = 2), mydriasis (n = 2) vs. miosis (n = 3)] were noticed. Prompt response to naloxone in two cases and lack of response in one patient were observed. All patients survived and the effect of intoxication wore off within two days. Kratom overdose toxidrome is variable and, in keeping with its receptor physiology, consists of signs and symptoms of opioid-like overdose, sympathetic overactivation and serotonin-like syndrome. Naloxone can help to avoid intubation in some cases.

An evaluation of adverse drug reactions and outcomes attributed to kratom in the US Food and Drug Administration Adverse Event Reporting System from January 2004 through September 2021

Kratom is a widely used Asian botanical that has gained popularity in the United States due to a perception that it can treat pain, anxiety, and opioid withdrawal symptoms. The American Kratom Association estimates 10-16 million people use kratom. Kratom-associated adverse drug reactions (ADRs) continue to be reported and raise concerns about the safety profile of kratom. However, studies are lacking that describe the overall pattern of kratom-associated adverse events and quantify the association between kratom and adverse events. ADRs reported to the US Food and Drug Administration Adverse Event Reporting System from January 2004 through September 2021 were used to address these knowledge gaps. Descriptive analysis was conducted to analyze kratom-related adverse reactions. Conservative pharmacovigilance signals based on observed-to-expected ratios with shrinkage were estimated by comparing kratom to all other natural products and drugs. Based on 489 deduplicated kratom-related ADR reports, users were young (mean age 35.5 years), and more often male (67.5%) than female patients (23.5%). Cases were predominantly reported since 2018 (94.2%). Fifty-two disproportionate reporting signals in 17 system-organ-class categories were generated. The observed/reported number of kratom-related accidental death reports was 63-fold greater than expected. There were eight strong signals related to addiction or drug withdrawal. An excess proportion of ADR reports were about kratom-related drug complaints, toxicity to various agents, and seizures. Although further research is needed to assess the safety of kratom, clinicians and consumers should be aware that real-world evidence points to potential safety threats.

Kratom Alkaloids: A Blueprint?

Alkaloids from the botanical Mitragyna speciosa (commonly referred to as "kratom") interact with opioid, adrenergic, serotonergic, and other receptors to provide myriad reported effects, including analgesia, energy, improved mood, and relaxation, among others. These alkaloids are complex and unique and may serve as a blueprint for the development of novel molecules to treat various substance use disorders.

Metabolism of Speciociliatine, an Overlooked Kratom Alkaloid for its Potential Pharmacological Effects

Speciociliatine, a diastereomer of mitragynine, is an indole-based alkaloid found in kratom (Mitragyna speciosa). Kratom has been widely used for the mitigation of pain and opioid dependence, as a mood enhancer, and/or as an energy booster. Speciociliatine is a partial µ-opioid agonist with a 3-fold higher binding affinity than mitragynine. Speciociliatine has been found to be a major circulating alkaloid in humans following oral administration of a kratom product. In this report, we have characterized the metabolism of speciociliatine in human and preclinical species (mouse, rat, dog, and cynomolgus monkey) liver microsomes and hepatocytes. Speciociliatine metabolized rapidly in monkey, rat, and mouse hepatocytes (in vitro half-life was 6.6 ± 0.2, 8.3 ± 1.1, 11.2 ± 0.7 min, respectively), while a slower metabolism was observed in human and dog hepatocytes (91.7 ± 12.8 and > 120 min, respectively). Speciociliatine underwent extensive metabolism, primarily through monooxidation and O-demethylation metabolic pathways in liver microsomes and hepatocytes across species. No human-specific or disproportionate metabolites of speciociliatine were found in human liver microsomes. The metabolism of speciociliatine was predominantly mediated by CYP3A4 with minor contributions by CYP2D6.