The five most addictive substances - and how they affect the brain Do you ever wonder what are the most physically addictive substances, and what they do to your brain? Researcher David Nutt wondered just that – so he and his colleagues worked on a classification system to rank addictive drugs on a 3 point scale. A 3 is the highest score, meaning the substance is maximally addictive. Here is a quick lowdown on what they found. 

With the exception of barbiturates, in every case the brain’s dopamine system is involved. Increasing dopamine levels or blocking dopamine inhibition are among the mechanisms in each of these addictive substances. 

Alcohol came in fifth, with a score of 1.9 out of 3 on the addiction scale, with barbiturates or “downers” the fourth most addictive substance. Drinkers get a steady dopamine increase with each subsequent drink. Barbiturates disrupt the flow of sodium ions in the brain, which prevents neurons from firing. This is why they cause the “downer” effects of sleepiness, calmness, and reduced heart rate and respiratory rates. 

Nicotine, the main component of tobacco, is the third most addictive substance. As with alcohol, dopamine is increased with each hit of nicotine to the bloodstream. 

Crack cocaine comes in at second place on the addiction scale. Cocaine works by blocking inhibitory dopamine receptors in the brain. That is, cocaine prevents the dopamine system from being able to turn off. 

With a perfect 3 out of 3 on Nutt’s scale, heroin reigns as the number one most addictive substance. Heroin can make dopamine levels rocket to 200% of normal, and even relatively low amounts can cause cardiac arrest and death. 

You can see Dr. Nutt’s research paper from The Lancet here.