The 5 most addictive substances on Earth – and booze and fags are more harmful than heroin
A drug's potential to be addictive can be judged on the harm it causes and the extent to which the drug activates the brain’s dopamine system
What are the most addictive drugs on Earth?
This question seems simple, but the answer depends on who you ask.
It can be judged on the harm it causes, the street value of the drug, the extent to which the drug activates the brain’s dopamine system, how pleasurable people report the drug to be.
A drug's potential to be addictive can also come down to the degree to which the drug causes withdrawal symptoms and how easily a person trying the drug will become hooked.
But there are other facets to measuring the addictive potential of a drug, too, and there are even researchers who argue that no drug is always addictive.
This is how the five most addictive substances on the planet effect your brain, Eric Bowman from the University of St Andrews writes for
1. Alcohol
Although legal in the US and UK, alcohol was scored a 1.9 out of a maximum of three for addictiveness in a recent study.
The study, by Professor David Nutt, looked at how addictive substances were for the brain.
Alcohol has many effects on the brain, but in laboratory experiments on animals it increased dopamine levels in the brain’s reward system by 40-360 per cent – and the more the animals drank the more dopamine levels increased.
Some 22 per cent of people who have taken a drink will develop dependence on alcohol at some point during their life.
The World Health Organisation (WHO) has estimated that two billion people used alcohol in 2002 and more than 3m people died in 2012 due to damage to the body caused by drinking.
Alcohol has been ranked as the most damaging drug by other experts, too.
2. Cigarettes
Nicotine is the main addictive ingredient of tobacco.
When somebody smokes a cigarette, nicotine is rapidly absorbed by the lungs and delivered to the brain.
Nutt's expert panels rated nicotine as the third most addictive substance.
More than two-thirds of Americans who tried smoking reported becoming dependent during their life.
In 2002 the WHO estimated there were more than one billion smokers and it has been estimated that tobacco will kill more than 8m people annually by 2030.
Laboratory animals have the good sense not to smoke.
However, rats will press a button to receive nicotine directly into their bloodstream – and this causes dopamine levels in the brain’s reward system to rise by about 25-40 per cent.
3. Cocaine
Cocaine directly interferes with the brain’s use of dopamine to convey messages from one neuron to another.
In essence, cocaine prevents neurons from turning the dopamine signal off, resulting in an abnormal activation of the brain’s reward pathways.
In experiments on animals, cocaine caused dopamine levels to rise more than three times the normal level.
It is estimated that between 14-20m people worldwide use cocaine and that in 2009 the cocaine market was worth about $75 billion (£52 billion).
Crack cocaine has been ranked by experts as being the third most damaging drug and powdered cocaine, which causes a milder high, as the fifth most damaging.
About 21 per cent of people who try cocaine will become dependent on it at sometime in their life.
Cocaine is similar to other addictive stimulants, such as methamphetamine – which is becoming more of a problem as it becomes more widely available – and amphetamine.
4. Heroin
Nutt's study ranked heroin as the most addictive drug, giving it a score of three out of a maximum score of three.
Heroin is an opiate that causes the level of dopamine in the brain’s reward system to increase by up to 200 per cent in experimental animals.
In addition to being arguably the most addictive drug, heroin is dangerous, too, because the dose that can cause death is only five times greater than the dose required for a high.
Heroin also has been rated as the second most harmful drug in terms of damage to both users and to society.
The market for illegal opiates, including heroin, was estimated to be $68 billion (£47 billion) worldwide in 2009.
MORE ON ADDICTION
5. Barbiturates
Barbiturates – also known as blue bullets, gorillas, nembies, barbs and pink ladies – are a class of drugs that were initially used to treat anxiety and to induce sleep.
They interfere with chemical signalling in the brain, the effect of which is to shut down various brain regions.
At low doses, barbiturates cause euphoria, but at higher doses they can be lethal because they suppress breathing.
Barbiturate dependence was common when the drugs were easily available by prescription, but this has declined dramatically as other drugs have replaced them.
This highlights the role that the context plays in addiction: if an addictive drug is not widely available, it can do little harm.
Nutt and his expert panels rated barbiturates as the fourth most addictive substance.
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