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What is caffeine?

Caffeine (1, 3, 7- trimethylxanthine) is a toxin that some plants produce to defend themselves. Small amounts are not harmful to humans, but have stimulant effects, making users feel more alert and energised. Typical use of the drug comes from caffeinated drinks such as coffee and tea, and also soft drinks such as cola and ‘energy drinks’.

Like other stimulant drugs such as cocaine, caffeine in high enough doses can harm and kill. However caffeine useis very much safer and more manageable than the use of cocaine and other potent stimulants, and only exceptionally rarely causes serious harm.

What are the different forms of product containing caffeine?

Caffeinated drinks (generally low risks of harm).

Caffeine is found in drinks like coffee, tea, and mate (a tea drunk in Argentina). Caffeine can also be found in ‘energy drinks’ which have high caffeine content, and some soft drinks. In Europe, drinks (not based on coffee or tea) with a caffeine content of more than 150 mg per litre, have to be labelled as high caffeine content with the amount of caffeine on it.

Shops also sell caffine shots, which are small amounts of sugary drink with a high caffeine content. Like alcohol shots, it is easy to drink a lot of these quickly before realising you have had too much.

It is common to become addicted to caffeinated drinks, in that stopping use will lead to withdrawal symptoms, although most people would not find it difficult to stop caffeine use.

Caffeine is often listed as a flavouring on soft drinks, although it may not be the case that caffeine adds to the taste of the drink, rather it increases the desire to consume it.

Caffeine tablets (low risk if used according to directions, potential for overdose if misused)

Caffeine tablets are legal and are used to increase alertness. Some beliefs about their effectiveness, for example in improving exam performance, are not wholly supported by the evidence. They do not replace the need for sleep, in fact a nap can be much more beneficial.

Caffeine as an adulterant in illegal drugs (could sometimes be harmful)

Analysis of drug samples show that caffeine is commonly added, which adds bulk cheaply and so increases the dealers’ profits. Caffeine has been identified in heroin, where it may make the drug easier to smoke. It is commonly added to stimulant drugs like cocaine, amphetamine (speed) and MDMA (ecstasy) where its stimulant effects may disguise how impure the drug is, and may also increase the risks.

How does caffeine work as a drug in the body and brain?

Caffeine hinders the action of the adenosine. Adenosine dampens down brain activity, so by getting in its way (competitive inhibition) caffeine stimulates many circuits in the brain.

Caffeine also works because we have powerful beliefs about its properties. If you consume caffeine without believing something like “I’m consuming caffeine which will make me more alert”, the caffeine may not increase your alertness at all.

What are the effects of caffeine?

Caffeine has stimulant effects and makes people more alert, reducing feelings of tiredness. It is widely believed to improve mental performance but the evidence for this is mixed.It has been suggested that the appearance of performance enhancement is because caffeine reverses withdrawal effects in regular users rather than improving overall mental ability. In people who are not regular users, any improvement is likely to be counteracted by anxiety and jitteriness which make it difficult to focus. Caffeine may in some circumstances increase a feeling of alertness whilst actually decreasing ability.

Caffeine causes sweating and also makes people urinate more, although tolerance to this effect develops quickly so people who, for example, drink coffee every morning usually do not find this to be a problem. Caffeine can also lead to difficulty sleeping (insomnia).

Some people become anxious or irritable after caffeine. Unpleasant feelings become more likely the higher the amount you consume.

Does caffeine have any medical uses?

Caffeine has a few medical uses. Its stimulant properties mean it is sometimes useful to keep premature babies breathing.

Caffeine is also an ingredient in common over the counter medications for flu, colds and headaches. It can sometimes make pain relief drugs work more quickly and effectively, and can counteract the drowsiness caused by some drugs. Caffeine does not treat colds, but can relieve the symptoms of sluggishness that often come with them.

What are the risks of using caffeine? Can they be avoided or reduced?

Low or moderate caffeine consumption has minimal risks.

Caffeine can cause insomnia so people often avoid it in the evenings so that they can sleep properly. The half-life of caffeine is around 5 hours, meaning that after a cup of coffee at 6pm, an individual will still have half the caffeine left in their body at 11pm, and a quarter at 4am, disrupting sleep. Individuals vary in their reaction to caffeine, so the half-life could be much longer or shorter than 5 hours.

Regular high intake of caffeine is thought to cause behavioural changes including restlessness and anxiety/nervousness. It may increase the frequency of headaches in some.

Very excessive caffeine consumption can be harmful and even fatal. Most people who suffer harm after consuming caffeine have taken excessive numbers of caffeine tablets, or consumed excessive quantities of highly caffeinated energy drinks, sometimes mixed with alcohol.

Taking too much caffeine results in symptoms similar to taking too much of a stimulant drug, with overdoses causing anxiety/agitation, convulsions, tremors and hallucinations. People admitted to hospital after taking large amounts of caffeine typically have tachycardia (fast heart beat) and hypertension (high blood pressure). Additionally, a common feature of caffeine overdose is vomiting, which can be very severe. Other gastrointestinal problems such as diarrhoea and stomach pains have also been reported. People have died from caffeine overdose, and some deaths have been associated with high caffeine content energy drinks.

Are there health conditions that might make caffeine more harmful?

Excessive use of energy drinks, especially with exercise, could be riskier for some people with heart problems.

People who suffer headaches and migraines might benefit from exploring the role of caffeine in these. Whilst caffeine is a useful component in some headache pills, both the drug itself and caffeine withdrawal could be triggers for headaches.

Caffeine can worsen symptoms in people who easily become anxious.

Mental health issues such as schizophrenia and bipolar disorder, even if they seem in remission, may be worsened by very excessive amounts of caffeine. The drug may bring on episodes of psychosis or suicidality.

Mixing caffeine with other drugs

Caffeine seems to increase harmful effects of MDMA and other psychostimulants (amphetamine, cocaine) in raising body temperature, lowering the seizure threshold and harmful effects on the heart. This is problematic as many illegally sold drugs may contain some caffeine, and people taking psychostimulant drugs may also have consumed caffeine.

It has been suggested that drinking energy drinks with alcohol makes people more prone to risky behaviour.This may be because caffeine makes people feel less drunk from alcohol, whilst not improving thing like coordination or judgement.

How addictive is caffeine?

Caffeine is a mildly addictive drug, tolerance to the drug does develop and people have reported withdrawal symptoms of: headache, tiredness/drowsiness, insomnia, stomach and joint pains and trouble concentrating. Caffeine withdrawal symptoms may be quite mild for most regular tea or coffee drinkers, who would most likely just get a bit irritable and headachy if they miss their morning cup.

What are the long-term impacts of caffeine to health and wellbeing?

Regular caffeine intake is not usually harmful and may even have some mildly beneficial effects.

ies have suggested that habitual consumption of caffeinated drinks may have a small protective effect against certain forms of cancer. Further research is needed. Additionally, one study found that coffee consumption (not decaf) is linked with a lower chance of depression in women.research is needed to confirm any beneficial uses of caffeine, and it is possible that other things in tea and coffee, or different lifestyles of their users, may play a part in these findings.

For regular use, any beneficial effects of caffeine in energy drinks or colas would be outweighed by harm of the sugar.

Caffeine harm reduction advice

As long as users recognise that caffeine is a drug and could be harmful in excessive amounts, caffeine poses a negligible risk to health.

How much are you taking?

Moderate caffeine use is not thought to be harmful, and may even be beneficial. Consumption of drinks like coffee or tea probably could not result in a caffeine overdose. Some ‘energy drinks’ can have very high caffeine contents, and should be used in moderation. Caffeine pills also may contain large amounts of caffeine (some contain up to 200mg of caffeine, which is like 4 cups of coffee). Check the label of energy drinks and tablets to judge how much caffeine you are taking.

Be aware that ‘legal highs’ and controlled drugs often contain caffeine. This is a problem as you do not know how much caffeine you are taking, and it could also increase the harms of some. One study of 6 ‘legal high’ products found that some contained around 90% caffeine. This means that taking one gram of the product would be like taking around 13 litres of cola, 3.75 litres of energy drink, or 12-15 cups of coffee.

You always need sleep

Caffeine improves some mental abilities in tired people, and many people use it to remain alert when they are tired. Caffeine is no substitute for sleep however, and not sleeping is harmful both psychologically and physically. Once the caffeine has worn off you are likely to ‘crash’ if you are very tired.


Being addicted to caffeine does not usually affect people’s lives for the worse. It does however mean that you can get withdrawal effects if you don’t have caffeine, which can be unpleasant. This would be worse for those who regularly have very large amounts of caffeine (which is easier to do with energy drinks and caffeine pills). A regular caffeine habit means that you are not necessarily making yourself more energised and alert than someone who doesn’t use caffeine, rather you need caffeine to maintain normal levels of energy and alertness. Frequent headaches can be related to caffeine withdrawal.

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