(-)Ephedrine and caffeine mutually potentiate one another's amphetamine-like stimulus effects

Clinically Relevant Herb-Drug Interactions: A 30-Year Historical Assessment

The Dietary Supplement Health and Education Act, a legislative measure ushering in a novel class of complementary healthcare products known as dietary supplements, will mark its 30th anniversary in October 2024. Over this 30-year period, dietary supplement usage evolved from a few hundred products made up mostly of vitamins, minerals, and select botanical extracts to more than 75,000 single- and multi-ingredient products that are now regular staples in the American healthcare system and used by half of all U.S. consumers. One of the fastest-growing segments of the dietary supplement market during this 3-decade interval has been those products formulated with botanical extracts. Coincident with the growing popularity of botanical dietary supplements (BDS) has been their concomitant ingestion with conventional prescription medications. BDS are complex mixtures of phytochemicals oftentimes exhibiting complex pharmacology. Formulated as concentrated phytochemical extracts, BDS are vehicles for a host of plant secondary metabolites rarely encountered in the typical diet. When taken with prescription drugs, BDS may give rise to clinically significant herb-drug interactions (HDI). Pharmacodynamic HDI describe interactions between phytochemicals and conventional medications at the drug receptor level, while pharmacokinetic HDI stem from phytochemical-mediated induction and/or inhibition of human drug metabolizing enzymes and/or transporters. This review summarizes BDS identified over the last 30 years that pose clinically relevant HDI and whose mechanisms are either pharmacodynamically or pharmacokinetically mediated.

Effects of adolescent caffeine consumption on cocaine self-administration and reinstatement of cocaine seeking

BACKGROUND:

Caffeine consumption by children and adolescents has risen dramatically in recent years, yet the lasting effects of caffeine consumption during adolescence remain poorly understood.

AIM:

These experiments explore the effects of adolescent caffeine consumption on cocaine self-administration and seeking using a rodent model.

METHODS:

Sprague-Dawley rats consumed caffeine for 28 days during the adolescent period. Following the caffeine consumption period, the caffeine solution was replaced with water for the remainder of the experiment. Age-matched control rats received water for the duration of the study. Behavioral testing in a cocaine self-administration procedure occurred during adulthood (postnatal days 62-82) to evaluate how adolescent caffeine exposure influenced the reinforcing properties of cocaine. Cocaine seeking was also tested during extinction training and reinstatement tests following cocaine self-administration.

RESULTS:

Adolescent caffeine consumption increased the acquisition of cocaine self-administration and increased performance on different schedules of reinforcement. Consumption of caffeine in adult rats did not produce similar enhancements in cocaine self-administration. Adolescent caffeine consumption also produced an upward shift in the U-shaped dose response curve on cocaine self-administration maintained on a within-session dose-response procedure. Adolescent caffeine consumption had no effect on cocaine seeking during extinction training or reinstatement of cocaine seeking by cues or cocaine.

CONCLUSIONS:

These findings suggest that caffeine consumption during adolescence may enhance the reinforcing properties of cocaine, leading to enhanced acquisition that may contribute to increased addiction vulnerability.

The 2014 Philip S. Portoghese Medicinal Chemistry Lectureship: The "Phenylalkylaminome" with a Focus on Selected Drugs of Abuse

The phenylalkylamine, particularly the phenylethylamine, moiety is a common structural feature found embedded in many clinically approved agents. Greater still is its occurrence in drugs of abuse. The simplest phenylethylamine, 2-phenylethylamine itself, is without significant central action when administered at moderate doses, but fairly simple structural modifications profoundly impact its pharmacology and result in large numbers of useful pharmacological tools, agents with therapeutic potential, and in drugs of abuse (e.g., hallucinogens, central stimulants, empathogens), the latter of which are the primary focus here. In vivo drug discrimination techniques and in vitro receptor/transporter methods have been applied to understand the actions of these phenylalkylamines and their mechanisms of action. Thus far, depending upon pendent substituents, certain receptors (e.g., serotonin receptors) and monoamine transporters (i.e., serotonin, dopamine, and norepinephrine transporters) have been implicated as playing major roles in the actions of these abused agents in a complex and, at times, interwoven manner.

Mechanisms of the psychostimulant effects of caffeine: implications for substance use disorders

BACKGROUND

The psychostimulant properties of caffeine are reviewed and compared with those of prototypical psychostimulants able to cause substance use disorders (SUD). Caffeine produces psychomotor-activating, reinforcing, and arousing effects, which depend on its ability to disinhibit the brake that endogenous adenosine imposes on the ascending dopamine and arousal systems.

OBJECTIVES

A model that considers the striatal adenosine A2A-dopamine D2 receptor heteromer as a key modulator of dopamine-dependent striatal functions (reward-oriented behavior and learning of stimulus-reward and reward-response associations) is introduced, which should explain most of the psychomotor and reinforcing effects of caffeine.

HIGHLIGHTS

The model can explain the caffeine-induced rotational behavior in rats with unilateral striatal dopamine denervation and the ability of caffeine to reverse the adipsic-aphagic syndrome in dopamine-deficient rodents. The model can also explain the weaker reinforcing effects and low abuse liability of caffeine, compared with prototypical psychostimulants. Finally, the model can explain the actual major societal dangers of caffeine: the ability of caffeine to potentiate the addictive and toxic effects of drugs of abuse, with the particularly alarming associations of caffeine (as adulterant) with cocaine, amphetamine derivatives, synthetic cathinones, and energy drinks with alcohol, and the higher sensitivity of children and adolescents to the psychostimulant effects of caffeine and its potential to increase vulnerability to SUD.

CONCLUSIONS

The striatal A2A-D2 receptor heteromer constitutes an unequivocal main pharmacological target of caffeine and provides the main mechanisms by which caffeine potentiates the acute and long-term effects of prototypical psychostimulants.

Coca-paste seized samples characterization: chemical analysis, stimulating effect in rats and relevance of caffeine as a major adulterant

Coca-paste (CP) is a drug of abuse that so far has not been extensively characterized. CP is an intermediate product of the cocaine alkaloid extraction process from coca leaves, hence it has a high content of cocaine base mixed with other chemical substances (impurities) and it is probably adulterated when it reaches the consumers. Despite its high prevalence and distribution through South America, little is known about its effects on the central nervous system. In the present study, a chemical analysis of CP samples from different police seizures was performed to determine the cocaine base content and the presence and content of impurities and adulterants. Some CP representative samples were selected to study the effects on the locomotor activity induced after acute systemic administration in rats as a measure of its stimulant action. The behavioral response was compared to equivalent doses of cocaine. As expected, cocaine was the main component in most of the CP samples assayed. Caffeine was the only active adulterant detected. Interestingly, several CP samples elicited a higher stimulant effect compared to that observed after cocaine when administered at equivalent doses of cocaine base. Combined treatment of cocaine and caffeine, as surrogate of different CP samples mimicked their stimulant effect. We demonstrated that cocaine and caffeine are the main components responsible for the CP-induced stimulant action while the contribution of the impurities was imperceptible.

Methylxanthines and drug dependence: a focus on interactions with substances of abuse

This chapter examines the psychostimulant actions of methylxanthines, with a focus on the consequences of their excessive use. Consumption of methylxanthines is pervasive and their use is often associated with that of substances known to produce dependence and to have abuse potential. Therefore, the consequences of this combined use are taken into consideration in order to evaluate whether, and to what extent, methylxanthines could influence dependence on or abuse of other centrally active substances, leading to either amplification or attenuation of their effects. Since the methylxanthine that mostly influences mental processes and readily induces psychostimulation is caffeine, this review mainly focuses on caffeine as a prototype of methylxanthine-produced dependence, examining, at the same time, the risks related to caffeine use.

Effects of chronic caffeine exposure on adenosinergic modulation of the discriminative-stimulus effects of nicotine, methamphetamine, and cocaine in rats

RATIONALE

Adenosine receptors are involved in cocaine and methamphetamine discrimination and exposure to caffeine can affect behavioral effects of nicotine in rats.

OBJECTIVES

Here we investigated the relative involvement of adenosine A(1) and A(2A) receptors in nicotine, cocaine, and methamphetamine discrimination, before and/or during chronic caffeine exposure.

MATERIALS AND METHODS

The nonselective adenosine receptor antagonist caffeine, the A(1)-receptor antagonist cyclopentyltheophylline (CPT), and the A(2A)-receptor antagonist MSX-3 were evaluated in rats trained to discriminate 0.4 mg/kg nicotine from saline under a fixed-ratio schedule of food delivery. Effects of adenosine receptor antagonists were then compared in rats discriminating nicotine, methamphetamine, or cocaine from saline during chronic caffeine exposure in their drinking water.

RESULTS

Caffeine, CPT, and MSX-3 partially generalized to nicotine and shifted nicotine dose-response curves leftwards. During chronic caffeine exposure, however, all three ligands failed to generalize to nicotine and failed to shift nicotine dose-response curves. In previous experiments, CPT and MSX-3 partially generalized to methamphetamine and cocaine and shifted dose-response curves leftwards. In the present experiments, CPT neither generalized nor shifted dose-response curves for methamphetamine or cocaine during chronic caffeine exposure. However, MSX-3 partially generalized to both psychostimulants and shifted their dose-response curves leftwards. Caffeine partially generalized to cocaine, but not methamphetamine, and shifted both dose-response curves leftwards.

CONCLUSIONS

Both adenosine A(1) and A(2A) receptors are capable of modulating the discriminative-stimulus effects of nicotine. Chronic caffeine exposure produces complete tolerance to both A(1)- and A(2A)-mediated effects in nicotine-trained rats. In contrast, chronic caffeine exposure produces tolerance to adenosine A(1)-mediated, but not A(2A)-mediated, effects in methamphetamine- and cocaine-trained rats.

Changes in sensitivity of response distributions to changing reinforcement ratios during exposure to ephedrine, caffeine, and ephedrine-caffeine combinations

Changes in the sensitivity of response distributions to changes in reward distribution (reinforcer distribution sensitivity) were examined when rats were exposed to low and moderate doses of caffeine, ephedrine, and caffeine-ephedrine combinations. The data show significant decreases in sensitivity in response distributions to changes in reward schedule values during exposure to caffeine and ephedrine/caffeine combinations, whereas ephedrine alone resulted in overmatching comparable with baseline and NaCl conditions. Rats treated either with 3.0-mg/kg or 10.0-mg/kg doses of caffeine and all combinations of ephedrine at doses of 1.8 or 5.6 mg/kg with caffeine at 3.0 or 10.0 mg/kg showed reduced sensitivity in response distributions to differences in reinforcement schedule ratios. In contrast, when rats were exposed to ephedrine at 1.8 or 5.6 mg/kg, they maintained or increased the degree of overmatching. Although reinforcer distribution sensitivity was altered, drug exposure did not significantly affect the absolute rates of responding. Bias varied after exposure to caffeine, ephedrine, and their combinations, but not systematically. Finally, whereas the estimates of goodness of fit (r2) to the matching equation showed some decreases during drug exposure, these were neither statistically significant nor correlated with drug dose. These results suggest differential effects of ephedrine and caffeine on the sensitivity of response distributions to changes in reinforcement ratio distributions, with deleterious effects of caffeine and ephedrine/caffeine combinations.

Dopamine-mediated actions of ephedrine in the rat substantia nigra

Although ephedrine is a centrally active stimulant, its effect on midbrain dopamine neurons is not known. To study the effect of ephedrine on dopamine-containing cells, current-clamp microelectrode recordings were made from substantia nigra pars compacta (SNC) neurons in horizontal brain slice preparations. Ephedrine (100-1000 microM) slowed spontaneous firing and produced a modest concentration-dependent hyperpolarization of membrane potential (EC50 279 microM), with a concomitant net decrease in membrane resistance. These effects were blocked by the D2-like dopamine antagonist sulpiride (1 microM). Electrically evoked inhibitory synaptic potentials mediated by GABAB receptors were reduced 28% by ephedrine. However, ephedrine did not reduce fast synaptic potentials mediated by GABAA or ionotropic glutamate receptors. Inhibition of the GABAB response appeared to be mediated by a postsynaptic mechanism because ephedrine also reduced baclofen-induced hyperpolarization by 28%. Both ephedrine-induced hyperpolarization and inhibition of baclofen-induced hyperpolarization were abolished when slices were superfused with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT). Despite perfusion with AMPT, the ability of ephedrine to cause hyperpolarization was restored after perfusing the slice with dopamine (30 microM). Taken together, these results suggest that ephedrine causes hyperpolarization and suppresses GABAB receptor-mediated effects by releasing endogenous dopamine. However, the high concentrations required to observe these effects in vitro suggest that biologically relevant central effects of ephedrine are more likely to be mediated either by non-dopamine systems, such as those involving noradrenaline, or by dopamine systems outside the SNC.

Stimulus properties of nicotine, amphetamine, and chlordiazepoxide as positive features in a pavlovian appetitive discrimination task in rats

Recent experiments from our laboratory have demonstrated that drug states can signal when environmental cues will be followed by rewarding outcomes (ie Pavlovian conditioning). However, little is known about the generality of this approach and whether it can be used for studying the pharmacological properties of drug states. Accordingly, the present experiments tested the pharmacological specificity of nicotine (0.4 mg/kg), amphetamine (1 mg/kg), and chlordiazepoxide (CDP, 5 mg/kg) in this Pavlovian drug discrimination procedure. Following drug administration, presentation of a conditional stimulus (CS) was followed by brief access to sucrose. When saline was administered, the same CS was presented but sucrose was withheld. In substitution tests, rats in each condition received varying doses of all training drugs and caffeine. Anticipatory food seeking developed during the CS on drug sessions but not on saline sessions for all drug features (ie drug state-specific conditional response (CR)). In generalization tests, this CR decreased as a function of decreases in the training dose. Median effective doses (ED50s) were calculated for nicotine (0.054 mg/kg), amphetamine (0.26 mg/kg), and CDP (2.48 mg/kg). No compound tested substituted for the CDP training drug. Partial substitution was evident between nicotine and amphetamine; CDP did not substitute for either of these drug features. Caffeine fully substituted for nicotine (ED50 = 15.45 mg/kg) and amphetamine (ED50 = 3.70 mg/kg), but not for CDP. These results are consistent with the hypothesis that drug states can occasion appetitive Pavlovian CRs in a pharmacologically specific manner.

Ephedra-containing dietary supplements in the US versus ephedra as a Chinese medicine

Ephedra has been commonly used in traditional Chinese medicine (TCM) without significant adverse effects. Ephedra-containing dietary supplements are widely used in the United States to promote weight reduction and energy enhancement. However, there are significant safety concerns regarding the use of ephedra-containing dietary supplements, especially when such use occurs by consumers without medical supervision. This article reviews and contrasts the usage of ephedra as a dietary supplement in the US against an herbal medication in TCM. The potential adverse effects of ephedra-containing dietary supplements are also reviewed.

Discriminative stimulus effects of (-)-ephedrine in rats: analysis with catecholamine transporter and receptor ligands

A drug discrimination procedure was used to examine the neuropharmacology of (-)-ephedrine (5 mg/kg), a sympathomimetic amine found in a variety of dietary supplements. (-)-Ephedrine has caused concern because of its use as a precursor in the manufacture of street drugs (e.g. methamphetamine) and its potential for abuse and toxicity. In the present study, the catecholamine reuptake inhibitors mazindol and nomifensine, the norepinephrine (NE) reuptake inhibitor desipramine, and the dopamine D(2)-like (e.g. D(2), D(3) and D(4)) agonist quinpirole substituted for (-)-ephedrine (>/=80% (-)-ephedrine-lever responding). The NE reuptake inhibitor nisoxetine, the D(1)-like (e.g. D(1) and D(5)) agonists (+/-)-SKF 38393 and SKF 82958, and the mixed D(1)-/D(2)-like agonist apomorphine occasioned intermediate levels of responding (50-79% (-)-ephedrine-lever responding). The (-)-ephedrine cue was antagonized by the D(1)-like antagonist SCH 23390 and the alpha(1)-adrenoceptor antagonist prazosin as well as the D(2)-like antagonists (-)-eticlopride and haloperidol, although only at doses that disrupted responding in some rats. The discriminative stimulus effects of a small dose of (-)-ephedrine (1.25 mg/kg) were enhanced by the alpha(2)-adrenoceptor antagonist idazoxan and to a lesser extent by the beta-adrenoceptor antagonist (-)-propranolol. However, the alpha(2)-adrenoceptor agonist clonidine (0.04 mg/kg) did not attenuate the (-)-ephedrine stimulus. These results suggest that D(1)-, D(2)-like, and alpha(1)-adrenergic receptors mediate the discriminative stimulus effects of (-)-ephedrine. Substitution of desipramine for (-)-ephedrine and not for some other stimulants suggests that NE transmission is a prominent feature of the (-)-ephedrine discriminative stimulus, and that NE underlies therapeutic and abuse-related effects of (-)-ephedrine that diverge from those of other stimulants.

Supplements and drugs used to enhance athletic performance

The temptation of using drugs and supplements as shortcuts to improving athletic performance or even to enhance appearance is very seductive to adolescents. This age group is often characterized by a desire for quick results and a lack of concern for future consequences. Preventing the use of drugs to enhance athletic performance is difficult even when we have good medical and scientific evidence to prove a dangerous risk-benefit ratio, such as with AASs. The use of "nutritional supplements" is even more difficult to control. The protection of these substances by the Dietary Supplement Health and Education Act of 1994 removed control of these substances from the FDA. Therefore, release and widespread use of new supplements occurs before significant clinical study of benefit and adverse effects takes place. The distributors' financial interest, the products' promotional claims, and the athletes' and coaches' insatiable desire to win at all costs are a volatile combination. This spawns the production of a huge number of "natural" products, making it even more difficult to assess efficacy, safety, legality, and purity of these substances. Health care professionals need to rely on research when available, stay current on trends in athletes' drug and supplement use, and discuss the individual athlete's concerns when they arise. The preparticipation physical examination can be a good opportunity for discussion. Finally, physicians need to educate athletes, parents, coaches, trainers, and other physicians. A reasonable strength and conditioning program and a well-balanced diet must be presented as a sensible alternative to a riskier, shortcut mindset.

Reinforcing and discriminative-stimulus effects of ephedrine isomers in rhesus monkeys

Ephedrine is a sympathomimetic drug that is currently found in many over-the-counter preparations. This compound exists as four isomers which, in addition to a racemic mixture, were evaluated for their positive reinforcing effects and for their similarity to (+)-amphetamine as a discriminative stimulus. Rhesus monkeys (N=3) with intravenous cocaine (0.1 mg/kg/inj) or saline as a consequence for lever pressing were shown to self-administer all of the ephedrine compounds (range tested: 0.03-3.0 mg/kg/inj), with the exception of (-)-pseudoephedrine, when each drug/dose was substituted for cocaine or saline during test sessions. However, the (-)-pseudoephedrine isomer was evaluated within a limited dose range due to solubility limitations. Systematically increasing the number of responses required for an injection indicated that these isomers were not as effective as reinforcers as was cocaine. Rhesus monkeys (N=3) trained to discriminate intragastric 1.0 mg/kg (+)-amphetamine from saline were given substitution tests with the ephedrine isomers and the racemic mixture. When given intragastrically, at least one dose of all the ephedrine isomers substituted for the (+)-amphetamine discriminative stimulus in at least one of the subjects tested. However, (+)-amphetamine-like effects were not systematically related to dose. When the discriminative-stimulus effects of (-)-ephedrine were also compared with those of (+)-amphetamine across three different routes of administration, full, dose-related, (+)-amphetamine-like responding was observed with both the intramuscular and intravenous routes. Taken together, these results suggest that the ephedrines have psychomotor stimulant-like abuse potential, lower than that of cocaine. Parenteral administration may enhance psychomotor-stimulant-like effects.

Herbal Medicines and Epilepsy: The Potential for Benefit and Adverse Effects

The widespread availability and use of herbal medicines raise the potential for adverse effects in the epilepsy population. Herbal sedatives (kava, valerian, chamomile, passionflower) may potentiate the effects of antiepileptic medications, increasing their sedative and cognitive effects. Despite some antiseizure effects in animal models, they should not be used in place of standard seizure medications because efficacy has not been established. Anecdotal, uncontrolled observations suggest that herbal stimulants containing ephedrine (ephedra or ma huang) and caffeine (cocoa, coffee, tea, maté, guarana, cola or kola) can exacerbate seizures in people with epilepsy, especially when taken in combination. Ginkgo and ginseng may also exacerbate seizures although the evidence for this is similarly anecdotal and uncertain. St. John's wort has the potential to alter medication pharmacokinetics and the seizure threshold. The essential oils of many plants contain epileptogenic compounds. There is mixed evidence for evening primrose and borage lowering the seizure threshold. Education of both health care providers and patients is the best way to avoid unintentional and unnecessary adverse reactions to herbal medicines.

Stimulus effects of phenylpropanolamine optical isomers in (+)amphetamine-trained rats

There are eight phenylpropanolamine optical isomers related in structure to the central stimulants methamphetamine and amphetamine. Some of these are quite well known, such as (-)ephedrine, whereas others are relatively obscure, such as (-)cathine. Although certain of these phenylpropanolamines, such as (-)ephedrine and (+)cathine, retain central stimulant activity and are about 10- to 25-fold less potent than (+)amphetamine, the eight phenylpropanolamines have been compared only once before in drug discrimination studies. This latter study employed (-)ephedrine as the training drug. Because there are striking similarities between (-)ephedrine and (+)amphetamine as training drugs, it was of interest to determine and compare the effect of all eight phenylpropanolamines in (+)amphetamine trained animals. Using rats trained to discriminate 1 mg/kg of (+)amphetamine from saline vehicle under a variable interval 15-s (VI 15-s) schedule of reinforcement, the (+)amphetamine stimulus generalized only to (-)ephedrine (ED(50) = 4. 5 mg/kg) and (+)cathine (ED(50) = 8.0 mg/kg), and both agents were at least 10 times less potent that (+)amphetamine (ED(50) = 0.37 mg/kg). These results stand in contrast to those obtained with the (-)ephedrine-trained animals where the ephedrine stimulus generalized to all of the phenylpropanolamines except for (-)pseudoephedrine and (-)cathine. It is concluded that although there might be some similarity between the (-)ephedrine and (+)amphetamine stimuli, there are clear differences between them as determined in tests of stimulus generalization under the conditions employed.

(+)Amphetamine-stimulus generalization to an herbal ephedrine product

We have previously demonstrated that a (+)amphetamine stimulus generalizes both to (-)ephedrine and caffeine. Using rats trained to discriminate intraperitoneal (IP) administration of 1.0 mg/kg of (+)amphetamine (ED(50) = 0.4 mg/kg) from saline vehicle in a standard two-lever drug discrimination procedure, the present investigation shows that the (+)amphetamine stimulus generalizes to (+)amphetamine (ED(50) = 1.0 mg/kg) when administered via the intragastric (IG) route, and that (+)amphetamine appears about 2. 5-fold less potent when administered via the IG route compared to the IP route. Likewise, (-)ephedrine (ED(50) = 10.8 mg/kg) and caffeine (ED(50) = 32.9 mg/kg) are also 2.5-fold less potent when administered via the IG route compared to their potency when administered via the IP route. The (+)amphetamine stimulus also generalizes to an IG-administered herbal preparation (i.e., Herbal XTC; the herbal preparation possesses an approximate potency roughly comparable to what might have been expected on the basis of its reported ephedrine and/or caffeine content. These results demonstrate, for the first time, that an ephedrine-containing herbal preparation can produce a (+)amphetamine-like effect in animals.

Arylalkylamine drugs of abuse: an overview of drug discrimination studies

Abused arylalkylamines fall into two major categories: the indolealkylamines, and the phenylalkylamines: These agents can be further subclassified on the basis of chemical structure. Examples of these agents possess hallucinogenic, stimulant, and other actions. Drug-discrimination techniques have been used to classify and investigate this large family of agents. Such studies have allowed the formulation of structure-activity relationships and investigations of mechanisms of action. Arylalkylamine designer drugs also possess the same or a combination of actions, and are being investigated by the same methods.