Insight: The five most addictive substances in the world

The five most addictive substances in the world

Chances are, you’ve tried at least two of these addictive substances. Here’s how they affect your brain.

1. Heroin

Heroin is an opiate that causes the level of dopamine in the brain’s reward system to increase by up to 200% 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.

2. 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.

3. Nicotine

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 et al’s expert panels rated nicotine (tobacco) as the third most addictive substance.

4. Barbiturates (“downers”)

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.

5. Alcohol

Although legal in the US and UK, alcohol was scored by Nutt et al.’s experts 1.9 out of a maximum of 3. 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% to 360% — and the more the animals drank the more dopamine levels increased.

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