Drugs provide their effects by altering the way in which the central nervous system (CNS) operates. The CNS is the brain and spinal cord. The effects fall into one of three broad categories of depressant, stimulant or psychedelic. More on how the drugs work within the CNS is given in the section of this program called 'Drugs and the Brain'.

slow down mental activity and physical functions, such as heart rate and breathing. They produce feelings of warmth and relaxation. Examples of depressant drugs are alcohol, tranquillisers, heroin and the opiates.

have the opposite effect of speeding up mental activity and physical functions, producing feelings of excitement and confidence. Examples of stimulant drugs are nicotine, caffeine, cocaine and amphetamines.

Both types of drug can also produce feelings of euphoria, a mood of wellbeing and great contentment.

on the other hand, usually have little effect on physical functions, as they work directly on those parts of the brain which control how the senses operate. They can alter the way in which the individual drug user perceives both their inner and outer worlds. LSD is an example of a psychedelic drug.

Drug, set and setting.

How these effects show themselves and how the drug feels to the individual is the result of a complex interaction between the properties of the substance itself (drug), the individual drug taker's mood, experience and expectations (set), and the environment within which the drug is taken (setting).

This trinity was first described by the American psychologist, Norman Zinberg, in his book 'Drug, Set and Setting', and provides a useful model to help in the understanding of drug use and the effects which drug users experience. The properties of the drugs have been described above and in the section on 'Drugs and the Brain'. The impact of set and setting are discussed below.

It all depends.
At first it seems difficult to understand how the setting of drug use or the mood or expectation of the user can influence the effects the user has from the drug. To understand this better consider the use of identical doses of the depressant drug alcohol, in three different settings.

The first setting is that of a romantic candlelit dinner for two at home - perhaps a wedding anniversary. Over a good dinner a fine bottle of claret is consumed and the result is a pleasant, mellow drug experience in very familiar surroundings. These compliment the atmosphere of affection and quiet satisfaction. Both users expect to have a pleasant and relaxed time, enjoying the drug experience - and they probably will.

In the second example the same red wine is drunk but by a person sitting alone in a corner of an unfamiliar and rowdy pub in the aftermath of a relationship breaking up. In this case the alcohol is there to 'drown the sorrows'. It is much more likely that the user would become more depressed the more they drink and maybe even become sullen and angry. The drug experience would probably be utterly different from before.

In the third case the bottle of red wine is taken along to a lively New Years Eve party where just about everyone is up on their feet dancing to rock or rave music. Now the disinhibiting effect of alcohol will most likely come to the fore and merge and support the general atmosphere. Its New Year's Eve and its time to PARTY!!

In this setting and with these expectations alcohol may feel more like a stimulant than a depressant drug and lead to great energy being expended in dancing the night away.

The exceptions.

In all these examples there is the possibility of contradictory effects in exceptional circumstances. If far too much of the drug alcohol is taken, its underlying properties will come to the fore. If someone drinks too much they will eventually fall down and maybe pass out. In exceptional cases they may even literally drink themselves to death. The same is true with other drugs. At high dose levels the drug's chemical effect will dominate.

But most of the time this does not happen with alcohol, nor with other drugs. In most episodes of drug taking, whatever the drug, the drug effects are interpreted maybe even translated by the user through their previous experience of the drug. This frames their expectation of a given effect and this is either supported or undermined by the setting in which the drug use takes place.

There are also quirky individual responses to all drugs including alcohol. Some people always 'turn nasty' or even violent when under the influence of alcohol. Usually they have some underlying resentment or anger they are bottling up. When the drug takes the lid off - it all comes boiling out.
Strangely this seems to happen much more with the drug alcohol than with most other depressant drugs although it has been noted that some stimulants and steroid drugs can reveal or provoke violence and aggression in some users.

If this seems a bit complicated - it is! The effects of drug use are conditional. It depends how much is taken, of what drug, how often, in what doses, in what settings, with what experience, in what mood and with what expectation.


As the body becomes used to a drug, tolerance to the effects can build up. This means that increased doses are required to achieve the desired effect.


Some drugs, when used regularly over an extended period, can produce physical and/or psychological dependence or addiction.

Psychological dependence is an emotional craving for a drug to which the body has become accustomed. Physical dependence means the body has adapted to the drug and it is likely that withdrawal symptoms will follow when the drug is no longer taken.

Drugs with a potential for physical dependence include the opiates (heroin, morphine, etc.), opioids (synthetic opiate like drugs such as methadone and palfium), the benzodiazepines - so called 'minor tranquillisers' (valium, librium, etc.) and alcohol. There are also the stimulant drugs with severe dependency potential. These include nicotine, cocaine, amphetamine and caffeine.