Why does antipsychotic Olanzapine (Zyprexa) increase appetite and cause weight gain

Zyprexa or Olanzapine is an Antipsychotic medication prescribed for schizophrenia, bipolar disorder and depression with psychotic features. It is an atypical antipsychotic medication. That means it is a second generation antipsychotics with apparently fewer side effects. It lacks troublesome side effects such as muscle twitching, abnormal movements that are seen in conventional anti-psychotics such as Haldol.

However, they are known to cause some other troublesome side effects such as diabetes mellitus, weight gain and blood lipid abnormalities that lead to heart attacks.

Zyprexa increases body weight through several mechanisms. One such is increased appetite. Most patients who take Zyprexa complain of increased appetite. According to clinical trials, it is independent to the effect seen following the cure of psychosis (Psychosis/schizophrenia/depression known to cause loss of appetite).

In addition, Zyprexa inhibits Histamine 1 receptors in the brain, which leads to increased appetite and weight gain. Another action that explains its ability to cause diabetes mellitus is the pancreatic M3 receptor blockade. This causes reduced insulin secretion which leads to diabetes mellitus, increased blood lipid levels and ultimately weight gain.

Due to these risky side effects, patients who take Zyprexa should check their blood glucose, blood lipid levels and body weight frequently. They should undergo proper weight reduction program.

As with any weight loss program, the patient should change their life style. In addition, reduced intake of high caloric food and increased exercises can help to reduce the weight gain associated with Zyprexa. Other option would be to change into another drug which causes less weight gain. But most antipsychotics can cause some weight gain. Good antipsychotic with less risk of weight gain is Abilify.

Sources

Prescribing guide – Stephen stahl