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NEUROSCIENCE OF PSYCHOACTIVE SUBSTANCE USE AND DEPENDENCE

Projects such as the South African Community Epidemiology Network on
Drug Use (SACENDU) and its related regional network have been started to
address this lack of information.
The data in Table 1.3 show that 2.5% of the total global population and
3.5% of people 15 years and above had used cannabis at least once in a year
between 1998 and 2001. In many developed countries, for example Canada,
the USA and European countries, more than 2% of youths reported heroin
use and almost 5% reported smoking cocaine in their lifetime. Indeed, 8% of
youths in western Europe and more than 20% of those in the USA have
reported using at least one type of illicit drug other than cannabis (UNODCCP,
2002). There is evidence of rapid increases in the use of amphetamine-type
stimulants among teenagers in Asia and Europe. Injecting drug use is also a
growing phenomenon, with implications for the spread of HIV infections in
an increasing number of countries.
The nonmedical use of medications (e.g. benzodiazepines, pain killers,
amphetamines, etc.) is known to be fairly common but global statistics are
lacking.

Adverse effects of psychoactive substances and
their mechanisms of action
In the majority of cases, people use psychoactive substances because they
expect to benefit from their use, whether through the experience of pleasure
or the avoidance of pain. The benefit is not necessarily gained directly from
the psychoactive action of the substance. Someone drinking beer with
colleagues may be more motivated by the feeling of fellowship this brings
than by the psychoactive effect of the ethanol.
However, the psychoactive effect is nevertheless present, and is usually at
least peripherally involved in the decision to use.
In spite of the real or apparent benefits, the use of psychoactive substances
also carries with it the potential for harm, whether in the short term or long
term. Such harm can result from the cumulative amount of psychoactive
substance used, for example, the toxic effect of alcohol in producing liver
cirrhosis. Harmful effects can also result from the pattern of use, or from the
form or medium in which it is taken (see Fig. 1.2). Pattern of use is of obvious
importance – for instance, in the case of deaths due to overdose – not only in
terms of the amount on a particular occasion, but also in terms of the context
of use (e.g. heroin use accompanied by heavy alcohol use). The form or
medium of use may also be crucially important. Most of the adverse health
effects of tobacco smoking, for instance, come not from the nicotine itself,
but from the tars and carbon monoxide which are released when nicotine is
taken in cigarette form. Similarly, the adverse effects from taking the drug by
injection are evident in the case of heroin use.
The main harmful effects due to substance use can be divided into four
categories (see Fig. 1.2). First there are the chronic health effects. For alcohol

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Chapter_1 10 19.1.2004, 11:23