Effects of Drugs on the Brain

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Many people seem to have a constant desire to alter their state of consciousness using drugs.  They use stimulant drugs to help them stay awake and dance the night away.  Others use sedatives to calm their nerves.  Or even substances that enable them to experience new forms of consciousness and to forget the troubles of everyday life.

All of these drugs interact in different ways with neurotransmitter and other chemical messenger systems in the brain.  In many cases, the drugs hijack natural brain systems that have to do with pleasure and reward – psychological processes that are important in eating, drinking, and sex and even learning and memory.

Effects of Drugs on the Brain

The Path to Addiction and Dependence

Drugs that act on the brain or the blood supply of the brain can be invaluable – such as those that relieve pain. Recreational drug use has a very different purpose, and the problem with it is that it can lead to abuse.  The user can, all too easily, become dependent or even addicted.  He or she will then suffer very unpleasant physical and psychological withdrawal symptoms when they interrupt their drug habit.

This state of dependence can lead a user to crave the drug, even though doing so is clearly damaging to their work, health and family.  In extreme cases the user may be drawn into crime in order to pay for the drug.

Fortunately not everyone who takes a recreational drug becomes dependent on it.  Drugs differ in their dependence liability – ranging from high risk in the case of cocaine, heroin and nicotine to lower risk in the case of alcohol, cannabis, ecstasy and amphetamines.

During the development of drug dependence the body and brain slowly adapt to the repeated presence of the drug, but exactly what changes go on in the brain remain mysteries.  Although the primary sites of action of heroin, amphetamines, nicotine, cocaine and cannabis are all different, these drugs share an ability to promote the release of the chemical messenger dopamine in certain brain regions. 

Although this is not necessarily akin to triggering a “pleasure” mechanism, it is thought that the drug-induced release of dopamine may be an important final common pathway of “pleasure” in the brain.  It represents the signal that prompts a person to carry on taking the drug.


Alcohol acts on neurotransmitter systems in the brain to dampen down excitatory messages and promote inhibition of neural activity. Alcohol’s action proceeds through stages of relaxation and good humour, after one drink, through to sleepiness and loss of consciousness. That is why the police are so strict about drinking and driving, and why there is so much public support for this strict attitude.  

Some people become very aggressive and even violent when they drink, and about one in ten of regular drinkers will become dependent alcoholics. Long-term alcohol use damages the body, especially the liver, and can cause permanent damage to the brain. Pregnant mothers who drink run the risk of having babies with damaged brains and low IQ’s.


Nicotine is the active ingredient in all tobacco products. Nicotine acts on brain receptors that normally recognise the neurotransmitter acetylcholine; it tends to activate natural alerting mechanisms in the brain. Given this, it’s not surprising that smokers say that cigarettes help them concentrate and have a soothing effect.

The trouble is that nicotine is highly addictive and many inveterate smokers continue to smoke for no better reason than to avoid the unpleasant signs of withdrawal if they stop.  The pleasure has long gone. While there appears to be no deleterious effect on the brain, tobacco smoke is extremely damaging to the lungs and long-term exposure can lead to lung cancer and also to other lung and heart diseases.


Cannabis presents us with a puzzle, for it acts on an important natural system in the brain that uses neurotransmitters that are chemically very like cannabis. This system has to do with the control of muscles and regulating pain sensitivity. Used wisely, and in a medical context, cannabis can be a very useful drug. 


Cannabis is an intoxicant which can be pleasurable and relaxing, and it can cause a dream-like state in which one’s perception of sounds, colours and time is subtly altered.  No-one seems to have died from an overdose, although some users may experience unpleasant panic attacks after large doses. 

Some people believe it should be legalised – and doing so could cut the link between supply of the drug and that of other much more dangerous drugs. Unfortunately, as with nicotine, smoking is the most effective way of delivering it to the body.  Cannabis smoke contains much the same mixture of poisons as cigarettes (and is often smoked with tobacco).

Cannabis smokers tend to develop lung diseases and they run the risk of developing lung cancer – although this has not yet been proved.  About one in ten users may become dependent, which people who sell the drug are well aware of. Repeated heavy use is incompatible with the skill of driving and with intellectually demanding work; experiments have established that people intoxicated with cannabis are unable to carry out complex mental tasks.  Although not yet proven, there is some evidence that heavy use by young people might trigger the mental illness schizophrenia in susceptible individuals.


Amphetamines are man-made chemicals that include “Dexedrine”, “Speed”, and the methamphetamine derivative called “Ecstasy”. These drugs act in the brain by causing the release two naturally occurring neurotransmitters.  One is dopamine – which probably explains the strong arousal and pleasurable effects of amphetamines. 

The other is serotonin – which is thought to account for their ability to cause a sense of well-being and a dream-like state that can include hallucinations. Dexedrine and Speed promote mainly dopamine release, Ecstasy more serotonin. The even more powerful hallucinogen d-LSD also acts on serotonin mechanisms in the brain. 

Amphetamines are powerful psychostimulants and they can be dangerous – especially in overdose.  Animal experiments have shown that Ecstasy can cause a prolonged, perhaps permanent reduction of serotonin cells.  This might account for the “mid-week blues” suffered by weekend ecstasy users. Frightening schizophrenia like psychosis can happen after Dexedrine and Speed.  You might be lured into thinking that Speed could help you in an exam – but don’t.  It won’t.


Heroin is a man-made chemical derivative of the plant product morphine.  Like cannabis, heroin hijacks a system in the brain that employs naturally occurring neurotransmitters known as endorphins. These are important in pain control – and so drugs that copy their actions are very valuable in medicine. 

Heroin is injected or smoked whereupon it causes an immediate pleasurable sensation – possibly due to an effect of endorphins on reward mechanisms.  It is highly addictive, but, as dependence develops, these pleasurable sensations quickly subside to be replaced by an incessant “craving”.  It is a very dangerous drug that can kill in even modest overdose (it suppresses breathing reflexes). Heroin has ruined many people’s lives.


Cocaine is another plant-derived chemical which can cause intensely pleasurable sensations as well as acting as a powerful psychostimulant.  Like the amphetamines, cocaine makes more dopamine and serotonin available in the brain. However, like heroin, cocaine is a very dangerous drug. People intoxicated with it, especially the smoked form called “crack”, can readily become violent and aggressive, and there is a life-threatening risk of overdose. The dependence liability is high, and the costs of maintaining a cocaine habit draw many users into crime.

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