Alcohol, heroin and cocaine are considered to be the most addictive drugs. In general, however, addiction depends on who is asked. According to different researchers, the possibility for a drug to be addictive can be measured in terms of the harm it does, the cost of the drug, and the potential of the drug to activate the brain’s dopamine system.

The extent of pleasure people reports following use were also taken into consideration, as well as the degree to which the drug can cause withdrawal symptoms, and how quickly a person trying the drug will become addicted.

There are other important criteria for gauging the addictive potential of a drug. However, numerous researchers around the globe claim that no drug is permanently addictive. Given the diverging views of researchers, the best way of ranking addictive drugs is to ask a panel of experts. In 2007, David Nutt and his colleagues revealed information after collating addiction experts’ answers to their inquiries, based on the criteria established.

Alcohol, although legal in most countries, was rated by addiction experts as the most addictive drug. While it has many effects on the brain, laboratory experiments using mice revealed that the most notable is its ability to cause higher dopamine levels in the brain’s reward system by 40 to 360 percent. The figure is significantly higher than most other substances that are considered addictive.

Heroin ranked as the second most addictive drug, giving it a rating of 2.5 out of a maximum score of 3. Heroin is an opiate that increases the level of dopamine in the brain’s reward system by over 200 percent. In addition to being an addictive drug, heroin is also dangerous, because the lethal dose is only five times greater than the one required for a high, Stuff reported.

Cocaine, on the other hand, directly changes the brain’s use of dopamine by transferring messages from one neuron to another, as well as stop neurons from turning off the dopamine signal. This results in abnormal behavior in the brain’s reward pathways. In animal experiments, cocaine caused dopamine levels to soar more than three times the usual level, Economist reported.

Alcohol may be the most circulated drug, but the cocaine market is worth higher. Possibly between 14 to 20 million people worldwide are cocaine users. In 2009, overall cocaine transactions made about $75 billion.