The US Food and Drug Administration is warning consumers not to purchase or use any tianeptine products, saying it continues to receive reports of severe adverse events, including death, linked to the substance.

Some lawmakers have urged FDA Commissioner Dr. Robert Califf to take immediate action on the use of tianeptine products, citing the need for more research on its effects.

The antidepressant is prescribed in Europe, Asia and Latin America to treat major depressive disorder, according to the FDA. However, it is not approved for use in the US, and tianeptine products are often sold illegally online and at gas stations, vape shops and smoke shops.

In the US, tianeptine products are often marketed as dietary supplements that can improve brain function and treat conditions including anxiety, depression, pain and opioid use disorder, the FDA says.

Some people use tianeptine as an opioid alternative or to self-treat anxiety or depression, according to the FDA. Side effects may include agitation, drowsiness, confusion, sweating, rapid heartbeat, high blood pressure, nausea, vomiting, slowed or stopped breathing, coma and death.