In the search to explain why some people become addicted while others don’t, one answer has been that some people have an addictive personality i.e. they are just more likely to become addicted. Support for this idea comes from the phenomenon of ‘addiction transfer’, described in a recent article by Samantha Murphy in the New Scientist (8 September 2012). Addiction transfer refers to the phenomenon that an addict may manage to overcome one addiction but then develops another as a kind of substitute. The addict appears to need to have an addiction. Accidental evidence for addiction transfer comes from studies of people who have undergone weight loss surgery. Overeating can be regarded as a kind of addiction and weight loss surgery cuts obese people off from their original addiction. Researchers estimate that about 15-30% of those who have undergone weight loss surgery transfer to a new addiction.

The explanation outlined in Murphy’s article is that addiction activates the brain reward system and, when this activation stops, the person looks for something else to maintain activity within this reward system. The genetic link in the addiction transfer explanation is that some people are born with lower levels of D2 receptors, resulting in lower levels of dopamine in the reward system. Addiction behaviour has the effect of increasing their dopamine levels, thus explaining why some people are more prone to becoming addicted. Critically this explains why some people, once they have experienced an addiction, need to continue some kind of addictive behaviour if the original one stops.