Tianeptine — commonly referred to as “gas station heroin” — has seen a “rapid and marked increase” in the U.S. illicit drug market, according to the Drug Enforcement Administration. There has been a recent increase in calls to poison control centers regarding the usage of this supplement, the DEA continued, which it called an “extreme public health concern.” Despite the warnings, tianeptine is still legal in most U.S. states.

What is tianeptine? Tianeptine is not currently approved by the Federal Drug Administration, according to the DEA, but is used as an antidepressant in Asia, Europe and Latin America, per the Recovery Centers of America. Common names for the drug include “ZaZa, Tianna, and Red Dawn,” according to the Mississippi State Department of Health.

The supplement doesn’t increase serotonin, as most antidepressants do, but primarily works by affecting the brain’s opioid and glutamate receptors. When misused and taken in high dosages, tianeptine functions similarly to opioids and morphine, the Recovery Centers of America said.

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Details: Tianeptine is currently legal and can even be found in gas stations across 43 U.S. states. The drug is illegal in Alabama, Georgia, Michigan, Minnesota, and Tennessee, and was banned in Ohio on Wednesday, Vice reported.

Despite being marked as extremely dangerous by several federal health organizations, tianeptine is being sold under a sort of legal loophole.

Dr. Shan Yin, the Medical Director of Cincinnati Drug and Poison Information Center told Fox 19 Cincinnati that tianeptine can avoid FDA regulation because it is being sold as a dietary supplement.

“By selling [tianeptine] as a dietary supplement, it somewhat circumvents the FDA, in that the FDA does not regulate it,” Dr. Yin said. “It’s somewhat complicated in terms of the law. But the FDA does not strictly regulate dietary supplements.”

Dangers of tianeptine: According to Vice, people use often use tianeptine as a way to quit harsher substances. However, the FDA reports that the drug can cause serious health issues.

The FDA states that withdrawals from the drug can mimic the symptoms of opioid toxicity withdrawal, and when taken in high quantities — alone or with other medications — it can cause “agitation, drowsiness, confusion, sweating, rapid heartbeat, high blood pressure, nausea, vomiting, slowed or stopped breathing, coma and death.” The DEA even claims that the drug is contributing to the country’s opioid epidemic.

What you should know: The FDA does not recommend the use of tianeptine to treat depression, even though the drug has been marketed to treat the disorder. Those experiencing depression or other conditions should talk to a health provider and go through approved channels of treatment.

Tianeptine is not a safe substance, the FDA emphasized, and the administration noted that it is taking action to discourage the marketing of the drug. Tianeptine can be addictive and cause severe withdrawal symptoms. Anyone struggling with addiction related to tianeptine or other substances can find addiction help at findtreatment.samhsa.gov.