Licit/illicit drugs

The United Nations drug control conventions do not recognize a distinction between licit and illicit drug, they describe only use to be licit or illicit. Here, the term illicit drugs is used to describe drugs which are under international control (and which may or may not have licit medical purposes) but which are produced, trafficked and/or consumed illicitly.

The main categories are:


Opiates is the generic name given to a group which includes naturally occurring drugs derived from the opium poppy (Papaver somniferum) such as opium, morphine and codeine, semi-synthetic substances such as heroin (the foregoing are opiates in the strictly correct definition); and opioids - 'opiate-like', wholly synthetic products such as methadone, pethidine and fentanyl. Opiates depress the central nervous system and are used therapeutically as analgesics (painkillers), as cough suppressants and against diarrhoea; in non medical usage as euphoriants and as a means of reducing anxiety, boredom, physical or emotional pain. Heroin is often the opiate preferred by consumers because it is relatively potent, easily dissolved in water for injecting and penetrates the blood-brain barrier more quickly than morphine. Effects may last from 4-6 hours. Heroin can also be snorted, smoked or inhaled by the method known as "chasing the dragon" whereby it is heated on foil and the fumes inhaled.

It can happen that opiate dependence brings few physical complications other than constipation, but such cases are rare; studies of British heroin addicts in the 1960s showed that even when maintained on medically prescribed "clean" heroin and supplied with needles they had a much higher death rate than the rest of the population. Frequent side effects of high doses of opiates are a reduction in sexual drive and fertility, resulting in impotence in men and severe irregularities in the female menstrual cycle, as well as mood instability, lethargy and anorexia. Individuals may develop tolerance of some, but not all the effects of opiates. Withdrawal symptoms are generally not life-threatening (if the individual is otherwise healthy) but are extremely unpleasant for a period of 48-72 hours.

Some of the most severe effects of heroin abuse stem less from the drug itself than from unhygienic injecting practices which cause hepatitis, HIV and AIDS and the wider diffusion of these diseases by sexual contact. It is generally believed that injecting heroin users are more severely dependent than inhalers, partly because injection is the least safe but most cost-effective way of using an illicit drug. It is also possible to take more of the drug by injection - inhalers tend to fall asleep before they reach the point of overdose. Switching between different routes is quite common, however, and may well be prompted by health considerations.

Other Central Nervous System Depressants:

This category includes barbiturates, nonbarbiturate depressants and benzodiazepines; they are also referred to as sedative-hypnotics. They can be used therapeutically as anaesthetics, anticonvulsants, in the treatment of tension and anxiety, insomnia and some psychiatric illnesses. The first major type of drug in this group to be manufactured was the barbiturate group, synthetic pharmaceuticals which since the 1960s have largely been replaced therapeutically by benzodiazapines such as diazepam (Valium). Benzodiazapines and non-barbiturate sedatives such as methaqualone appear regularly on the illicit market and are used for sedation and for pleasurable intoxication, often in combination with alcohol.

Barbiturates are powerful CNS depressants; they can cause excessive drowsiness and thereby put the user at risk if driving or operating machinery. Abuse may lead to respiratory problems such as bronchitis and emphysema and at high doses can cause unconsciousness or death through respiratory failure. Sudden withdrawal can also cause death. One of the greatest dangers of the barbiturate group is that as physical tolerance increases, the proportional difference between an effective dose and a lethal dose decreases. For this reason the barbiturate user is especially vulnerable to overdose.

Abuse of benzodiazepines can have adverse consequences for the cognitive functions such as memory and concentration. Moreover, individuals may develop tolerance and dependence, even through therapeutic doses, if taken over a long time. Withdrawal symptoms include anxiety, insomnia and restlessness. Although considered to be much less dangerous than the barbiturates, the recent trend of injecting benzodiazepines has caused particular concern because the drug does not dissolve in the blood stream.

Central Nervous System Stimulants:

Central nervous system stimulants include naturally occurring plants such as coca (Erythroxylum coca), khat and betel nuts (which are not under international control), products extracted from the leaf of the coca bush - coca paste, cocaine hydrochloride and crack cocaine - and wholly synthetic substances in the form of amphetamine and amphetamine-type compounds. Cocaine has some therapeutic value as a local anaesthetic, while some synthetic stimulants are used as anorectics (slimming pills), in the treatment of narcolepsy and of children suffering from attention deficit disorder. The non-medical reasons for using these substances include to elevate mood, to overcome fatigue and to improve performance. The effects of cocaine last from a few minutes to less than an hour, whereas the effects of amphetamine-type stimulants (ATS) may last several hours. Cocaine (hydrochloride) can be injected, but more commonly it is snorted, whereas crack cocaine is usually smoked. ATS can be taken orally, injected, smoked or snorted.

As with the opiates, stimulant-related morbidity may also be a function of the dose, frequency of use and administration route. Snorting cocaine can lead to septal necrosis (the erosion and death of tissue between the nostrils) and atrophy of the nasal mucus; smoking crack cocaine is associated with a risk of burns from flammable materials, with chronic bronchitis and with searing of pulmonary tissue. Crack smoking is thought to be associated with higher levels of dependency than cocaine snorting, but experts disagree as to whether it leads to more or less dependence than injection of cocaine hydrochloride.

The withdrawal symptoms associated with intensive stimulant abuse are unlike those related to opiates in that the body does not become physiologically dependent, but they may produce a state of acute unease or discomfort, depression, fatigue, insomnia and an intense desire for more of the drug. These symptoms are generally worse for amphetamines than for cocaine, though they may well occur after a cocaine or crack 'binge' that lasts several days, when the user may neither sleep nor eat. There is no consensus in the scientific literature on a single definition of cocaine dependency or of cocaine tolerance: there is some evidence of individuals developing a tolerance for cocaine but in general this is short-lived, such that users who abstain even for short periods will start with low doses. Tolerance quickly develops for amphetamine, however.

Cocaine overdoses most commonly occur when the user overestimates his/her own tolerance to the drug, or if other drugs are taken at the same time. Death from respiratory arrest can occur after large doses, especially if taken with a depressant drug.

Some CNS stimulants have hallucinogenic and communication-enhancing effects such as MDA (3,4-methylenedioxy-amphetamine) and MDMA (3,4-methylenedioxy-methamphetaime) and are commonly taken to heighten emotional and sensory perceptions at parties and dance sessions. MDA and MDMA are usually taken orally but can also be injected. The abuse of hallucinogenic stimulants may cause a variety of psychological problems such as confusion, depression, anxiety and paranoia. Physical consequences include muscle tension, nausea, blurred vision, faintness, chills or sweating - symptoms which in many respects are similar to those of heatstroke. Overcompensation by drinking large quantities of water sometimes causes excessive rehydration and can lead to death. For several days after use muscle pain, fatigue and depression are common; long term use may damage the liver, brain and heart.


Hallucinogens include naturally occurring substances such as psilocybin (from the Psilocybe mexicana mushroom), mescaline (from the peyote cactus); semi-synthetics such as lysergic acid diethylamide, (LSD) and synthetics such as phencyclidine (PCP). Apart from some traditional uses and for rare therapeutic use in psychiatry, hallucinogens are taken illicitly for their mind-altering or 'psychedelic' effects. Even in small doses LSD causes perceptual distortions of time and place, visual hallucinations and synaesthesia (a merging of the senses such that sounds are "seen" and colours are "heard"). In comparison to the powerful sensory distortions, the physiological after-effects are relatively slight, but may include dizziness, disorientation, anxiety, depression and distressing flashbacks.

PCP produces euphoria but this is unlike that of opiates or stimulants; use is often accompanied by feelings of unreality, distortions of time and space, self-damaging behaviour and belligerent paranoia. Hallucinogens are usually taken orally. Repeated administration reduces the effect of the drug but physical dependence is not known to occur. Effects last up to 12 hours.


Cannabis has by far the highest rates of prevalence globally. It is mainly consumed as marijuana (the dried flowering tops of the Cannabis sativa plant), as hashish (resin from the plant), or as an oil extracted from the resin. These preparations are generally smoked, often mixed with tobacco in a cigarette or "joint", but they can also be swallowed. Cannabis is a sedative, but it also has hallucinogenic effects which may last up to several hours. The principal psychoactive ingredient is delta-9-tetrahydrocannabinol (THC), but there exists a wide variety of THC levels within the various strains of cannabis now grown. Cannabis is soluble in fat, metabolizes very slowly and - since the brain is largely made up of fatty substances - it remains in the body for up to one month after consumption. When smoked, the drug is absorbed quickly into the bloodstream and reaches the brain within seconds. Depending on the quantity and frequency of consumption, cannabis may impair motor coordination, shorten attention span, and modify perceptions of time and space. In low doses it has a relaxing and mood enhancing effect but in higher doses and/or in certain individuals it can cause anxiety, panic or paranoia. Smoking the drug carries a similar, and possibly aggravated series of risks to those associated with cigarette smoking and respiratory cancers, bronchial and cardiovascular problems and the increased likelihood of foetal and neonatal complications.