But there’s still a lot scientists don’t know — and that’s why the drug hasn’t been approved yet.
Though several doctors have prescribed low doses of the drug (off-label prescribing is legal), it’s unclear how much should be given for it to be safe — or how often it should be taken.
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Because ketamine’s effects usually wear off after a few days or weeks, patients often need to repeat use, but the long-term effects of the drug are still unknown.
According to Medscape, it's still unclear what about ketamine's biology triggers an antidepressant response in one day when most antidepressants usually need two weeks or longer to make an impact.
And what does ketamine do to the brain that antidepressants don’t do?
Still, "well over 3,000" patients in the US. and Canada have been treated with ketamine so far, Yale University psychiatry professor Gerard Sanacora told NPR.
When other doctors ask him how he can offer the drug to patients with limited information about its effects, Sanacora responds with this answer: "If you have patients that are likely to seriously injure themselves or kill themselves within a short period of time, and they've tried the standard treatments, how do you not offer this treatment?"
When depressed patients who have exhausted their options take ketamine, Sanacora said, 50-75 percent of them feel at least 50 percent better within one day.
Researchers are continuing to study the long-term effects of ketamine and other glutamate-modulating agents in treating severe depression.
According to NPR, ketamine’s “chemical sibling” esketamine is in the final phase of testing before it reaches the Food and Drug Administration for consideration.
Read more on NPR.com.