US health regulators warned doctors that prescribing a certain group of psychiatric drugs to seniors suffering from dementia can increase their risk of death.

Antipsychotic drugs are approved to treat schizophrenia and bipolar disease, but doctors frequently prescribe them to treat elderly patients with dementia.

The Food and Drug Administration's announcement was an update to a 2005 action, when regulators added warnings about increased heart attacks and pneumonia to drugs called atypical antipsychotics.

The medicines include blockbusters like Eli Lilly & Co's Zyprexa and Johnson & Johnson's Risperdal.

A report said yesterday those same risks apply to 11 older drugs known as typical antipsychotics, including Pfizer's Navane and Endo Pharmaceutical's Moban.

The drugs were developed in the 1950s and have largely been replaced by the newer medications, which are believed to have fewer side effects, such as tremors.

Under FDA's orders, both drug types will now carry boxed warnings, the most serious a drug can carry, describing their risks to dementia patients.

Analysts did not expect the announcement to negatively impact drug company earnings because the original antipsychotics are available as low-cost generics.

Federal officials have repeatedly urged doctors not to medicate seniors unnecessarily. About 20 per cent of seniors in nursing homes who receive antipsychotics have not been diagnosed with psychiatric problems, according to data released by Medicare earlier this year.