Gottesman (1991) conducted a meta-analysis of twin studies, and found that people had a 48% chance of developing schizophrenia if their identical twin had the condition. This reduced to 17% with non-identical twins. This suggests that schizophrenia could have a genetic basis.
Another explanation of abnormality is that it is caused by biochemical imbalance. For example, the dopamine hypothesis suggests that excess dopamine may cause schizophrenia. Evidence for this includes the effects of drugs such as amphetamines, which increase dopamine levels and can result in behaviour similar to schizophrenia. However, an alternative explanation is that people with schizophrenia are more sensitive to dopamine, rather than they have more of the chemical.
Because the medical model assumes there is a physical cause of abnormality, it uses physical treatments. These include drug therapy, electro-convulsive therapy (which is sometimes used in very severe depression) and psychosurgery such as prefrontal lobotomies.
One strength is that there is evidence supporting the view that there are physical causes underlying some psychological disorders. Physical therapies, such as drugs, have proved effective in treating psychological conditions. Antipsychotic drugs prescribed for schizophrenia are often effective in reducing positive symptoms such as hallucinations and delusions. In some cases, these treatments have enabled people to lead more independent lives. The effectiveness of drugs supports the idea that there are physical causes of psychological conditions.
However, there are problems associated with physical treatments. For example, drugs treat symptoms rather than the causes and so do not cure psychological disorders. They may also have serious side effects. Another weakness of the medical model is that there are ethical issues raised by the use of treatments like ECT. It may be difficult to gain informed consent for treatment from someone with a psychological problem, especially if they don’t have insight into the condition.
In conclusion, the medical model has provided evidence that there may be underlying physical causes of psychological disorders. The treatments derived from the approach are often effective, but can have unpleasant side effects and don’t provide a cure. However, despite its weaknesses, the strengths of the model have maintained its popularity.