Psychoactive drugs, such as alcohol, caffeine, amphetamine, mescaline, lysergic acid diethylamide (LSD), cannabis, chloral hydrate, theophylline, IBMX and others, have been studied on certain animals. It is believed that plants developed caffeine as a chemical defense against insects. [1]
Species that have been reported to consume alcohol in the wild include Bohemian waxwings, fruit bats, tree shrews, and bees, though there is no evidence that these species consume alcohol preferentially. [2] Anecdotal reports of drunken animals in the wild include moose, parrots, orangutans, and a badger. [3]
Cedar waxwing, bohemian waxwing, common starling are frequently studied species when examining the effects of alcohol consumption in birds. [4]
Cedar waxwings have been observed flying while intoxicated by alcohol from overwintered hawthorn pommes ("haws"), resulting in crashes that lead to their deaths. [5]
Wild chimpanzees in Bossou, Guinea, have been observed consuming fermented sap from the raffia palm (Raphia hookeri) from 1995 to 2012. They use simple tools to access the sap, which averages 3.1% ABV. This behavior suggests that ethanol does not deter feeding and indicates that the last common ancestor of African apes and humans likely consumed foods containing ethanol. [6]
Chimpanzees at Bossou consumed large amounts of ethanol and showed signs of intoxication. Although detailed behavioral data before and after drinking was rarely collected, some chimps rested right after consuming fermented sap. [6]
Ethanol serves as an energy source for the common fruit fly. [7]
A study on fruit flies ( Drosophila melanogaster ) found that male flies become more aggressive when exposed to ethanol-containing food sources. This increased aggression is linked to the odor of ethanol, which enhances sensory neuron activity related to aggression-promoting pheromones and boosts attraction to citrus scents. These findings provide insights into how fruit flies interact with their environment. [8]
In a study using D. melanogaster, researchers found that mating increases neuropeptide F (NPF) levels in male flies, while sexual deprivation decreases them. Manipulating the NPF system affects ethanol preference: activation reduces preference, and inhibition enhances it. Notably, artificially activating NPF neurons is rewarding on its own and diminishes the reward effect of ethanol. These findings suggest that the NPF-NPF receptor axis reflects the state of the fly's reward system and influences behavior. [9]
Ethanol is nutritious but highly intoxicating for most animals, which typically tolerate only up to 4% in their diet. However, a 2024 study found that oriental hornets fed sugary solutions containing 1% to 80% ethanol for a week showed no adverse effects on behavior or lifespan. [10]
In 1948, Swiss pharmacologist Peter N. Witt started his research on the effect of drugs on spiders. The initial motivation for the study was a request from his colleague, zoologist H. M. Peters, to shift the time when garden spiders build their webs from between 2:00 a.m. and 5:00 a.m., which was decidedly inconvenient for Peters, to earlier hours. [13] Witt tested spiders with a range of psychoactive drugs, including amphetamine, mescaline, strychnine, LSD, and caffeine, and found that the drugs affect the size and shape of the web rather than the time when it is built. At small doses of caffeine (10 μg/spider), the webs were smaller; the radii were uneven, but the regularity of the circles was unaffected. At higher doses (100 μg/spider), the shape changed more, and the web design became irregular. All the drugs tested reduced web regularity except for small doses (0.1–0.3 μg) of LSD, which increased web regularity. [12]
The drugs were administered by dissolving them in sugar water, and a drop of solution was touched to the spider's mouth. In some later studies, spiders were fed with drugged flies. [14] For qualitative studies, a well-defined volume of solution was administered through a fine syringe. The webs were photographed for the same spider before and after drugging. [12]
Witt's research was discontinued, but it became reinvigorated in 1984 after a paper by J.A. Nathanson in the journal Science , [15] which is discussed below. In 1995, a NASA research group repeated Witt's experiments on the effect of caffeine, benzedrine, marijuana and chloral hydrate on European garden spiders. NASA's results were qualitatively similar to those of Witt, but the novelty was that the pattern of the spider web was quantitatively analyzed with modern statistical tools, and proposed as a sensitive method of drug detection. [11] [16]
In 1984, Nathanson reported an effect of methylxanthines on larvae of the tobacco hornworm. He administered solutions of finely powdered tea leaves or coffee beans to the larvae and observed, at concentrations between 0.3 and 10% for coffee and 0.1 to 3% for tea, inhibition of feeding, associated with hyperactivity and tremor. At higher concentrations, larvae were killed within 24 hours. He repeated the experiments with purified caffeine and concluded that the drug was responsible for the effect, and the concentration differences between coffee beans and tea leaves originated from 2–3 times higher caffeine content in the latter. Similar action was observed for IBMX on mosquito larvae, mealworm larvae, butterfly larvae and milkweed bug nymphs, that is, inhibition of feeding and death at higher doses. Flour beetles were unaffected by IBMX up to 3% concentrations, but long-term experiments revealed suppression of reproductive activity. [15]
Further, Nathanson fed tobacco hornworm larvae with leaves sprayed with such psychoactive drugs as caffeine, formamidine pesticide didemethylchlordimeform (DDCDM), IBMX or theophylline. He observed a similar effect, namely inhibition of feeding followed by death. Nathanson concluded that caffeine and related methylxanthines could be natural pesticides developed by plants as protection against worms: Caffeine is found in many plant species, with high levels in seedlings that are still developing foliage, but are lacking mechanical protection; [17] caffeine paralyzes and kills certain insects feeding upon the plant. [15] High caffeine levels have also been found in the soil surrounding coffee bean seedlings. It is therefore understood that caffeine has a natural function, both as a Biopesticide and as an inhibitor of seed germination of other nearby coffee seedlings, thus giving it a better chance of survival. [18]
Coffee berry borers seem to be unaffected by caffeine, in that their feeding rate did not change when they were given leaves sprayed with caffeine solution. It was concluded that those beetles have adapted to caffeine. [19] This study was further developed by changing the solvent for caffeine. Although aqueous caffeine solutions had indeed no effect on the beetles, oleate emulsions of caffeine did inhibit their feeding, suggesting that even if certain insects have adjusted to some caffeine forms, they can be tricked by changing minor details, such as the drug solvent. [20]
These results and conclusions were confirmed by a similar study on slugs and snails. Cabbage leaves were sprayed with caffeine solutions and fed to Veronicella cubensis slugs and Zonitoides arboreus snails. Cabbage consumption reduced over time, followed by the death of the molluscs. [21] Inhibition of feeding by caffeine was also observed for caterpillars. [22]
"Tusko" was the name of a male Indian elephant at the Oklahoma City Zoo. On August 3, 1962, [23] researchers from the University of Oklahoma injected (human use involves oral ingestion) 297 mg of LSD to him, which is nearly three thousand times the human recreational dose (for an animal weighing roughly one hundred times as much as a human). [note 1] Within five minutes he collapsed to the ground and one hour and forty minutes later he died. It is believed that the LSD was the cause of his death, although some speculate that the drugs the researchers used in an attempt to revive him may have contributed to his death. [24] [25] [26] [27] [28] [29] In 1984 psychologist Ronald K. Siegel repeated the experiment with two elephants, using LSD only. Both survived. [29]
Bottlenose dolphins were administered LSD in the 1960s as part of NASA-funded experiments by John C. Lilly to study human–animal communication. The drug caused the animals to become more vocal, but did not enable meaningful communication. [30] [31] [32]
Macaque monkeys administered with the antipsychotics haloperidol and olanzapine over a 17–27 month period showed reduced brain volume. These results have not been observed in humans who also take the drug, due to the lack of available data. [33]
In a scientific study, researchers looked at how different drugs are self-administered by squirrel monkeys. The drugs they studied included cocaine and a few others that have some similarities to cocaine in how they affect the brain.
They trained the monkeys to give themselves these drugs through injections and observed their behavior. They wanted to see if the drugs had similar effects on the monkeys.
The results showed that cocaine and some of the other drugs had similar effects in maintaining the monkeys' self-administration behavior. However, one of the drugs, mazindol, didn't have the same effect on all the monkeys.
This suggests that the drugs that had similar effects may work in similar ways in the brain, affecting the monkeys' behavior in a comparable manner. The study also indicated that the reinforcing (addictive) and stimulating effects of these drugs might be related to how they interact with specific areas in the brain.
Overall, the research provides insights into how these drugs affect behavior and their potential for addiction. [34]
The researchers used a resident-intruder model to simulate social stress, with a focus on how social rank influenced the effects. The results showed that the confrontation influenced the monkeys' response to cocaine. When subordinate monkeys acted as intruders, their self-administration of low-dose cocaine increased, and their dose-response curve shifted to the left. In contrast, dominant monkeys experienced a decrease in cocaine self-administration and a rightward shift in the dose-response curve.
Brain glucose metabolism measurements revealed differences between dominant and subordinate monkeys, shedding light on the underlying mechanisms of these opposing behavioral effects. Dominant monkeys showed higher activity in brain regions related to visual processing, attention, and vigilance, while subordinate monkeys exhibited higher activity in areas linked to emotional processing and anxiety.
Both groups showed increased brain activity in regions associated with the reward system and stress response. Dominant monkeys also displayed higher aggression during the confrontations, suggesting that the opportunity to aggress might serve as a reinforcer.
The study indicated that the social context strongly influences behavior and drug effects, offering insights into individual differences in drug self-administration. It emphasized the need to consider the influence of social factors when developing treatments for cocaine use disorders, tailoring interventions to individuals based on their responses to social and environmental stressors. Understanding the neural and behavioral mechanisms at play in these scenarios can lead to more effective, personalized treatments for individuals with cocaine use disorders. [35]
Zebrafish have long acted as a model for humans to test the effects of various psychoactive substances. One study conducted by the Research Society on Alcoholism concluded that when given a moderate dose of ethanol, zebrafish became more active and swam faster. When the dose of alcohol increased, the zebrafish became sluggish. Another study by the same institute found that when a "drunk" (blood alcohol concentration of over 0.1) zebrafish is introduced to a group of sober ones, the sober fish will follow the drunk individual as their leader. [36]
In a study testing the effects of THC on memory in zebrafish, researchers found that THC impairs spatial memory but has no effect on associative memory. Zebrafish were able to remember color patterns associated with them getting fed after being put under the influence of THC, but were unable to remember the spatial pattern associated with them getting fed after being put under the influence of THC. [37]
Zebrafish have also been used to test the medicinal benefits of certain psychoactive drugs, particularly how they can be used to treat mental health problems. [38] A study looking into the antidepressant properties of ketamine using zebrafish as subjects found that when exposed to small amounts of ketamine (2 mg/L), zebrafish displayed more aggressive behavior. However, when the zebrafish were exposed to higher doses of ketamine (20 mg/L & 40 mg/L), their aggressive behavior subsided. Moreover, the highest dose of ketamine increased locomotion and circling behavior. [39] In another study testing the behavioral effects of LSD on zebrafish found that zebrafish that were exposed to the substance demonstrated increased inter-fish distance when shoaling, and had increased cortisol levels. These could show possible side effects of LSD if used as a therapeutic drug. [40]
A study conducted by the Aquaculture Institute looked into the effects of cannabis oil on the metabolism and immune system of the Nile tilapia (Oreochromis niloticus). They found that cannabis has no measurable effect on the white blood cell count or plasma protein concentration, and therefore has no effect on the immune system of the Nile tilapia. However, the tilapia that were fed food pellets laced with THC demonstrated a higher food conversion rate. This higher food conversion rate lead researchers to believe that THC increases the metabolic rate of Nile tilapia. [41]
Recreational drug use is the use of one or more psychoactive drugs to induce an altered state of consciousness, either for pleasure or for some other casual purpose or pastime. When a psychoactive drug enters the user's body, it induces an intoxicating effect. Recreational drugs are commonly divided into three categories: depressants, stimulants, and hallucinogens.
Psychopharmacology is the scientific study of the effects drugs have on mood, sensation, thinking, behavior, judgment and evaluation, and memory. It is distinguished from neuropsychopharmacology, which emphasizes the correlation between drug-induced changes in the functioning of cells in the nervous system and changes in consciousness and behavior.
Stimulants are a class of drugs that increase the activity of the brain. They are used for various purposes, such as enhancing alertness, attention, motivation, cognition, mood, and physical performance. Some of the most common stimulants are caffeine, nicotine, amphetamines, cocaine, methylphenidate, and modafinil.
Club drugs, also called rave drugs or party drugs, are a loosely defined category of recreational drugs which are associated with discothèques in the 1970s and nightclubs, dance clubs, electronic dance music (EDM) parties, and raves in the 1980s to today. Unlike many other categories, such as opiates and benzodiazepines, which are established according to pharmaceutical or chemical properties, club drugs are a "category of convenience", in which drugs are included due to the locations they are consumed and/or where the user goes while under the influence of the drugs. Club drugs are generally used by adolescents and young adults.
Disulfiram is a medication used to support the treatment of chronic alcoholism by producing an acute sensitivity to ethanol. Disulfiram works by inhibiting the enzyme aldehyde dehydrogenase, causing many of the effects of a hangover to be felt immediately following alcohol consumption. Disulfiram plus alcohol, even small amounts, produces flushing, throbbing in the head and neck, a throbbing headache, respiratory difficulty, nausea, copious vomiting, sweating, thirst, chest pain, palpitation, dyspnea, hyperventilation, fast heart rate, low blood pressure, fainting, marked uneasiness, weakness, vertigo, blurred vision, and confusion. In severe reactions there may be respiratory depression, cardiovascular collapse, abnormal heart rhythms, heart attack, acute congestive heart failure, unconsciousness, convulsions, and death.
In internal medicine, relapse or recidivism is a recurrence of a past condition. For example, multiple sclerosis and malaria often exhibit peaks of activity and sometimes very long periods of dormancy, followed by relapse or recrudescence.
Neuropharmacology is the study of how drugs affect function in the nervous system, and the neural mechanisms through which they influence behavior. There are two main branches of neuropharmacology: behavioral and molecular. Behavioral neuropharmacology focuses on the study of how drugs affect human behavior (neuropsychopharmacology), including the study of how drug dependence and addiction affect the human brain. Molecular neuropharmacology involves the study of neurons and their neurochemical interactions, with the overall goal of developing drugs that have beneficial effects on neurological function. Both of these fields are closely connected, since both are concerned with the interactions of neurotransmitters, neuropeptides, neurohormones, neuromodulators, enzymes, second messengers, co-transporters, ion channels, and receptor proteins in the central and peripheral nervous systems. Studying these interactions, researchers are developing drugs to treat many different neurological disorders, including pain, neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease, psychological disorders, addiction, and many others.
Caffeine dependence is a condition characterized by a set of criteria, including tolerance, withdrawal symptoms, persistent desire or unsuccessful efforts to control use, and continued use despite knowledge of adverse consequences attributed to caffeine. It can appear in physical dependence or psychological dependence, or both. Caffeine is one of the most common additives in many consumer products, including pills and beverages such as caffeinated alcoholic beverages, energy drinks, pain reliever medications, and colas. Caffeine is found naturally in various plants such as coffee and tea. Studies have found that 89 percent of adults in the U.S. consume on average 200 mg of caffeine daily. One area of concern that has been presented is the relationship between pregnancy and caffeine consumption. Repeated caffeine doses of 100 mg appeared to result in smaller size at birth in newborns. When looking at birth weight however, caffeine consumption did not appear to make an impact.
Cross-tolerance is a phenomenon that occurs when tolerance to the effects of a certain drug produces tolerance to another drug. It often happens between two drugs with similar functions or effects—for example, acting on the same cell receptor or affecting the transmission of certain neurotransmitters. Cross-tolerance has been observed with pharmaceutical drugs such as anti-anxiety agents and illicit substances, and sometimes the two of them together. Often, a person who uses one drug can be tolerant to a drug that has a completely different function. This phenomenon allows one to become tolerant to a drug that they have never used before.
QH-II-66 (QH-ii-066) is a sedative drug which is a benzodiazepine derivative. It produces some of the same effects as other benzodiazepines, but is much more selective than most other drugs of this class and so produces somewhat less sedation and ataxia than other related drugs such as diazepam and triazolam, although it still retains anticonvulsant effects.
Dimethocaine, also known as DMC or larocaine, is a compound with a stimulatory effect. This effect resembles that of cocaine, although dimethocaine appears to be less potent. Just like cocaine, dimethocaine is addictive due to its stimulation of the reward pathway in the brain. However, dimethocaine is a legal cocaine replacement in some countries and is even listed by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) under the category “synthetic cocaine derivatives”. The structure of dimethocaine, being a 4-aminobenzoic acid ester, resembles that of procaine. It is found as a white powder at room temperature.
RTI(-4229)-150, is a phenyltropane derivative which acts as a potent dopamine reuptake inhibitor and stimulant drug. It is around 5x more potent than cocaine, but is more selective for the dopamine transporter relative to the other monoamine transporters. RTI-150 has a fast onset of effects and short duration of action, and its abuse potential in animal studies is similar to that of cocaine itself; its main application in scientific research has been in studies investigating the influence of pharmacokinetics on the abuse potential of stimulant drugs, with the rapid entry of RTI-150 into the brain thought to be a key factor in producing its high propensity for development of dependence in animals. RTI-150 is not explicitly illegal anywhere in the world, but its similar structure and pharmacological activity to cocaine makes it possible that it would be considered a controlled substance analogue in countries such as the US, Canada, Australia and New Zealand which have controlled substance analogue legislation.
The short-term effects of alcohol consumption range from a decrease in anxiety and motor skills and euphoria at lower doses to intoxication (drunkenness), to stupor, unconsciousness, anterograde amnesia, and central nervous system depression at higher doses. Cell membranes are highly permeable to alcohol, so once it is in the bloodstream, it can diffuse into nearly every cell in the body.
Conditioned place preference (CPP) is a form of Pavlovian conditioning used to measure the motivational effects of objects or experiences. This motivation comes from the pleasurable aspect of the experience, so that the brain can be reminded of the context that surrounded the "encounter". By measuring the amount of time an animal spends in an area that has been associated with a stimulus, researchers can infer the animal's liking for the stimulus. This paradigm can also be used to measure conditioned place aversion with an identical procedure involving aversive stimuli instead. Both procedures usually involve mice or rats as subjects. This procedure can be used to measure extinction and reinstatement of the conditioned stimulus. Certain drugs are used in this paradigm to measure their reinforcing properties. Two different methods are used to choose the compartments to be conditioned, and these are biased vs. unbiased. The biased method allows the animal to explore the apparatus, and the compartment they least prefer is the one that the drug is administered in and the one they most prefer is the one where the vehicle is injected. This method allows the animal to choose the compartment they get the drug and vehicle. In comparison, the unbiased method does not allow the animal to choose what compartment they get the drug and vehicle in. Instead, the researcher chooses the compartments.
Self-administration is, in its medical sense, the process of a subject administering a pharmacological substance to themself. A clinical example of this is the subcutaneous "self-injection" of insulin by a diabetic patient.
SKF-97,541 is a compound used in scientific research which acts primarily as a selective GABAB receptor agonist. It has sedative effects in animal studies and is widely used in research into potential treatment of various types of drug addiction.
Prenatal cocaine exposure (PCE), theorized in the 1970s, occurs when a pregnant woman uses cocaine including crack cocaine and thereby exposes her fetus to the drug. Babies whose mothers used cocaine while pregnant supposedly have increased risk of several different health issues during growth and development and are colloquially known as crack babies.
A psychoactive drug, mind-altering drug, or consciousness-altering drug is a chemical substance that changes brain function and results in alterations in perception, mood, consciousness, cognition, or behavior. The term psychotropic drug is often used interchangeably, while some sources present narrower definitions. These substances may be used medically; recreationally; to purposefully improve performance or alter consciousness; as entheogens for ritual, spiritual, or shamanic purposes; or for research, including psychedelic therapy. Physicians and other healthcare practitioners prescribe psychoactive drugs from several categories for therapeutic purposes. These include anesthetics, analgesics, anticonvulsant and antiparkinsonian drugs as well as medications used to treat neuropsychiatric disorders, such as antidepressants, anxiolytics, antipsychotics, and stimulants. Some psychoactive substances may be used in detoxification and rehabilitation programs for persons dependent on or addicted to other psychoactive drugs.
Harris Isbell was an American pharmacologist and the director of research for the NIMH Addiction Research Center at the Public Health Service Hospital in Lexington, Kentucky from 1945 to 1963. He did extensive research on the physical and psychological effects of various drugs on humans. Early work investigated aspects of physical dependence with opiates and barbiturates, while later work investigated psychedelic drugs, including LSD. The research was extensively reported in academic journals such as the Journal of Pharmacology and Experimental Therapeutics, Psychopharmacologia, and the AMA Archives of Neurology and Psychiatry.
The Monkey Drug Trials of 1969 were a series of controversial animal testing experiments that were conducted on primates to study the effects of various psychoactive substances. The trials shed light on the profound effects of drug addiction and withdrawal in primates, pioneering critical insights into human substance abuse.