Diabetes and depression: a review

Antipsychotics

There are 2 strands of antipsychotic medications; First Generation Antipsychotics (FGAs), and Second Generation Antipsychotics (SGAs). FGAs are also known as typical antipsychotics, and SGAs as atypical antipsychotics. The difference with adverse effects appear to be that SGAs carry an increased risk of weight gain and Type II DM compared to FGAs (66). However, they have a lesser effect on the extrapyramidal system, and a more positive effect on depressive symptoms (compared to FGAs) and are therefore important in the treatment of some depressed patients (67). Olanzapine and Clozapine have been shown to cause patients to gain roughly 6kg in the first year of use. These drugs have also affect glucose regulation, which can induce the onset of DM. This is because dysregulation of glucose occurs as a result of insulin dysfunction, which can lead to hyperglycaemia - a sign of untreated DM (68).

One study has found that Clozapine in particular has a significant effect on the onset of DM in younger people (20-34 years old), with 5% of those taking Clozapine developing DM compared with only 2% of those using other antipsychotics. However, in other age groups there was no marked difference between using Clozapine versus any other antipsychotic (69).

It has been found that in patients taking atypical antipsychotics (SGAs) there is weight gain due to increased fat deposition in the body, leading to insulin resistance which causes DM (70). Another study found that Clozapine gives rise to a 7 fold greater chance of developing DM compared with conventional antipsychotics; Risperidone a 3.4 times greater risk; and Olanzapine a 3.2 times greater risk (71). Analysis of an UK General Practice Database, showed a six fold increase in the incidence of diabetes in those who had been prescribed Olanzapine at any point compared to controls not taking any antipsychotics and a fourfold increase compared to controls taking first generation antipsychotics (72, 73).

Data regarding the links between both antidepressants and antipsychotics with DM is somewhat limited to an extent. Trends suggest that they do induce the onset of DM, however evidence as to why this actually happens is inconclusive. Drugs must be further examined individually in order to understand the mechanisms by which they can encourage onset of DM.