A new antidepressant nasal spray approved by the Food and Drug Administration this month represents the first major innovation in depression medication in decades, according to ScienceNews.org.

Called Spravato, it’s based on the anesthetic ketamine, which is also popular for illicit use. And some psychiatrists are criticizing the FDA for what they say was a hasty approval based on data that raised unanswered questions about the drug.

Specifically, critics point toward insufficient data on the long-term effects of the drug, as well as what to expect when patients stop taking it.

At the same time, others are hailing the drug as a sorely needed new option for treatment. It’s intended for patients with severe depression, and doctors say there is a need for an alternative when other drugs have failed. It also takes effect within hours or days instead of weeks, like conventional antidepressants. Severe depression affects an estimated 5 million Americans.

Ketamine consists of esketamine and arketamine, two “mirror image” molecules, according to ScienceNews. Spravato uses only esketamine, which still has a potential for abuse and will face strict controls by the FDA. It was approved only for patients that have tried at least two other types of depression treatment.

And studies of its efficacy showed mixed results, with only one out of three month-long studies showing it to perform better than a placebo. For approval, the FDA relaxed its normal standards, which usually call for two short-term studies showing effectiveness.

In a longer, year-long study, relapsing depression occurred when patients switched from the drug to a placebo. For many, this raises unresolved questions over the effects of stopping the drug. Three participants in the studies committed suicide in the weeks after the studies ended.

However, the FDA said that the small study size and lack of similarities in the incidents made it “difficult to consider these deaths as drug-related” rather than a result of severe depression itself.

But critics, like Stanford University psychiatrist Alan Schatzberg, say there could be a connection.

“Are you inducing some sort of dependence? And when you get the people off, they feel lousy and could become suicidal?” he asked.

Furthermore, brain scans of people who have abused ketamine over a long period suggest it could lead to brain damage.

In the future, scientists hope to learn more about the fast-acting antidepressant properties of ketamine. National Institute of Mental Health neuroscientist Carlos Zarate, Jr. played a role in the first studies of ketamine’s antidepressant effects, and is now studying a molecule that’s produced when ketamine is processed inside the body. Animal experiments suggests it may offer some of the benefits without the risks.

But Zarate was careful to note that the prospects are unclear, saying “We still aren’t really sure what the key targets are in depression.”

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