Home            |        AS             |        A2          |         Links       |

Biological or medical model

It is worth mentioning at the outset that the medical model is generally better at explaining chemical addiction than it is behavioural and it is better at explaining maintenance of an addictive habit than its acquisition.

In attempting to explain addictive behaviour the medical model assumes the following:

Initiation is due to a genetic vulnerability or predisposition which is triggered by some environmental stressor

Maintenance is via the dopamine and the activities of the brain’s reward system

Relapse is due to physiological cravings and the need to avoid physical withdrawal symptoms

We shall consider each in turn. 

Genes and addiction (Initiation)

Clearly if there is a genetic factor we would expect to see trends for the disorder in families and similarities between people most closely related. 

Sarafino (1990) found that children born of alcoholic parents were four times more likely than usual to develop drinking problems themselves.  Clearly this in itself doesn’t rule out shared environment as a contributory factor, but the tendency still remained true even when the children had been adopted by non-alcoholic parents.

Agraval and Lynskey (2008) compared MZ and DZ twins and concluded that there was a moderate to high concordance rate (0.3 to 0.7) for addiction to a variety of drugs.  However, they also reported that age, gender and culture were also major contributory factors; all of which would be the same for MZ twins!

More recent research by Wendy Slutske (2010) has looked at the concordance rates of MZ and DZ twins in relation to gambling addiction.  She studied nearly 5,000 individuals and found that the concordance rate for MZ twins was twice as high as the concordance rate for DZ twins.  However, as she herself points out, it isn’t possible to isolate the genetic effects from environmental and social.  Instead she describes a ‘perfect storm’ of inherited vulnerability combined with the presence of gambling role models in the form of parents.  Slutske’s is also important in highlighting similar risks for both men and women.  Previous research has tended to focus on men. 

Specific genes

Slutske believes that between 10 and 100 individual genes may be involved in creating the vulnerability.  Modern techniques with DNA have allowed specific genes to be isolated for certain behaviours and conditions.  However, with psychological disorders these aren’t usually so clear cut.   Agraval et al (2008) believed that chromosomes 18 and 19 might be related to cannabis use.   Higuchi et al (2008) reported that Mpdz gene may predispose some animals to alcohol addiction.  I’ll consider the role of DRD2 in more detail on the next page.

Evaluation

Fowler (2007) looked at the cases of over 1000 twins and found that environmental and social factors were crucial in the initiating of addictive behaviours (including nicotine, alcohol and cannabis) whereas genetic and neurological factors were most closely linked with maintenance and the behaviours becoming heavier. 

Indirect effects

As with many behaviours, it may be difficult to pin down a specific gene as predisposing to a specific behaviour.  However, genes may be related to certain, broader personality types that then may predispose certain behaviours. 

With addiction, certain genes may predispose the individual to antisocial and attention seeking behaviour.  Attention seeking behaviour has been linked with alcoholism (Jang et al 2008) and with gambling (Comings et al 1996).

Evaluation of gene evidence

Some specific genes have been implicated in specific addictions, but then subsequent research has found that many with that addiction don’t possess that particular variant of gene. 

DRD2 variant A1

One such gene is the DRD2 gene that codes for D2 dopamine receptors.  This variant has been linked with smokers (48%), alcoholics (42%), gamblers (50%) as well as with other disorders, particularly autism.  However it is also found in 25% of the general population, many we have to assume have no obvious psychological or behavioural issues.

However, its role in dopamine pathways makes it an obvious candidate for involvement in addiction given the crucial role dopamine appears to play in the addiction process. 

Basically those with the A1 variant have significantly fewer dopamine receptors, so think about what that might mean in practice.  Fewer dopamine receptors would seem to suggest less pleasure!  It might therefore follow that to get the same amount of pleasure as a ‘normal’ brain the person would need to engage in more of the pleasurable behaviour, e.g. drink more alcohol. 

Next page