The answer to this question depends on whom you ask. Over time, scientists have tackled this matter from different perspectives, seeing that the potential for a drug to be addictive can be judged in terms of 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, the degree to which the drug causes withdrawal symptoms, and how easily a person trying the drug will become addicted to it.
Given the overwhelming variety of scientific views on the subject, in 2007, David Nutt, professor at University of Bristol, and his colleagues thought of a way of ranking addictive drugs by asking addiction experts. Here are the findings of their study:
- Heroin – This 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 in the world, it is highly dangerous, too, because what is considered to be a deadly dose is only five times greater than the dose required for a high.
- Cocaine – What this drug essentially does is preventing neurons from turning the dopamine signal off, resulting in an abnormal activation of the brain’s reward pathways. In experimental studies on animal subjects, cocaine caused dopamine levels to rise more than three times the normal level.
- Nicotine – When somebody smokes a cigarette, nicotine (the main addictive ingredient in tobacco) is quickly absorbed by the lungs and delivered to the brain. The World Health Organization estimated there were more than 1 billion smokers and it has been estimated that tobacco will kill more than 8 million people annually by 2030. Experimental studies found that 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%.
- Barbiturates (‘downers’) – Also known as blue bullets, gorillas, nembies, barbs and pink ladies – these drugs were initially used to treat anxiety and to induce sleep. They interfere with chemical signaling in the brain, which causes various brain region to shut down. At low doses, barbiturates cause euphoria, but at higher doses they can be lethal because they suppress breathing.
- Alcohol – Although legal in the many parts of the world, alcohol is still considered a highly addictive drug. It can have many effects on the brain, but in laboratory experiments on animals it increased dopamine levels in the brain’s reward system by 40-360% – and the more the animals drank the more dopamine levels increased. Other scientists consider alcohol to be the world’s most harmful drug.