Researchers discover why antipsychotic drugs cause weight gain

Researchers at Johns Hopkins University in Baltimore have discovered why some drugs used to treat mental illnesses such as schizophrenia, cause patients to gain a lot of weight.

The researchers say that antipsychotic medications such as Zyprexa increase the activity of an enzyme called AMPK in cells in the part of the brain that regulates eating behaviour.

The discovery was made in tests carried out in mice who were injected mice with clozapine (Clozaril), a drug commonly prescribed to treat schizophrenia and bipolar disorders in people who respond poorly to conventional drugs.

The researchers found that AMPK activity quadrupled in the mice after they were given clozapine.

The enzyme controls appetite in mice and is thought to do the same in humans.

According to the researchers the increase seen was big and occurred with very small doses of the drug.

Patients using antipsychotic drugs tend to put on so much weight that they are at heightened risk for serious complications including diabetes and heart disease.

Zyprexa, which is considered to be the best therapeutic agent, causes the most weight gain, and the research also showed that AMPK's increase was because the antipsychotic drugs were interfering with the important protein histamine, which is involved in allergy symptoms and long has been suspected to have a role in weight control.

The researchers are hopeful that the findings will lead to a new generation of antipsychotic drugs being developed that are just as effective but without the added weight gain.

The study is published in the Proceedings of the National Academy of Sciences.