compound mescaline. Since the mid- 1980s, MDMA has become a very popular recreational drug associated with live music venues, especially ‘rave’ parties. Ecstasy tab­lets come in a variety of shapes, sizes and colours. Doses and purity vary widely. A 2012 Dutch study found that the occurrence of significant adverse events after ecstasy use, for example, palpitations, agitation, hyperthermia and seizures, were attributed to the presence of contami­nants such as methylenedioxyamphetamine and meta­chlorophenylpiperazine. The effects of the drug occur after a latent period of 20–60 min and may last for 3–6 h. MDMA users report a state of relaxation and euphoria. The drug appears to increase empathy and to sharpen emotions. It decreases inhibitions and heightens the per­ception of sounds and colours.

but there is strong psychological dependence. Chronic exposure to solvents is likely to cause not only neurotox­icity but also hepatotoxicity and renal toxicity. Accidental death can also be caused by suffocation or choking on vomit after intense periods of sniffing that may trig­ger emesis. There is at present no treatment for solvent abuse. Changes in legislation which restricts sales of glues and solvents with high volatile organic compound content are an example of a means of controlling this type of addiction.

In the treatment of addiction there are three stages at which interventions play an important role: (1) during the active use of the drug, (2) to alleviate the symptoms of withdrawal and (3) to prevent relapse. That addic­tion is a disease of the brain, with complex physical and emotional aspects, is a relatively recent concept in the history of medicine; some scholars have proposed differ­ent theories of addiction and question or reject the brain disease model. For example, an alternative theory is that addiction reflects a distorted deep learning process that can be unlearned. Multiple drug addiction is a common and significant societal problem. Addicts may use, at the same time, varying combinations of alcohol, cocaine, crack, methadone and PCP, and also sniff glue. Each of these drugs, as discussed above, has its own characteris­tics and sometimes their negative effects can be synergis­tic. Cocaine and heroin can lead to tolerance. However, under certain conditions, drugs of abuse such as amphet­amine can lead to the opposite phenomenon, that of sen­sitization, that is, an enhancement of the effects of the drug. Ethanol and opiates lead to physical dependence, whereas cocaine and amphetamine much less so. Cues associated with drug taking play a major role in relapse, either a short time after abuse or after a long period of abstinence. Thus, places, people or the paraphernalia associated with drug abuse can trigger relapse. Stress also appears to act as a triggering factor for relapse in many addictions.