The drugs, which are intended to treat severe mental illness such as schizophrenia, can leave people in a stupor. The US Food and Drug Administration has issued black-box warnings - the agency’s most serious medication alert - about potentially fatal side effects when antipsychotics are taken by patients with dementia.

Nursing home regulators have for years collected data about individual homes’ use of antipsychotics but have not publicly released facility-specific information, citing patient privacy concerns. The government finally provided the data to the Globe, 19 months after the newspaper submitted a Freedom of Information Act request.

The data show that in more than one in five nursing homes in the United States, antipsychotics are administered to a significant percentage of residents despite the fact that they do not have a psychosis or related condition that nursing home regulators say warrants their use. The proportion of homes using antipsychotic drugs in this fashion is even higher in Massachusetts.

These findings are included in an interactive, online database assembled by the newspaper to allow consumers for the first time to compare nursing homes’ use of antipsychotics. (Find it at bostonglobe.com/nursinghome).

Physicians have wide latitude to prescribe drugs, even for purposes not approved by the FDA or recommended by the federal agency that regulates nursing homes, the Centers for Medicare & Medicaid Services.

Still, both agencies say it’s not appropriate in most cases for patients suffering from dementia to be prescribed antipsychotics. The medications increase the risk of lethal infections and cardiovascular complications in these elderly patients, the FDA says. In addition, the drugs can cause dizziness, a sudden drop in blood pressure, abnormal heart rhythms, blurred vision, and urinary problems.