Ketamine, a drug that’s shown promising results in a number of small studies as a treatment for depression, could be producing its effects by lighting up the brain’s opioid system, the circuitry that controls pain, reward, and sometimes addictive behavior, NPR reports. Researchers gave 12 people with treatment-resistant depression either a placebo or naltrexone, a drug that blocks opioid receptors, followed by a dose of ketamine. The naltrexone canceled out the antidepressive effects of the ketamine so completely that researchers cut the study short for ethical reasons, they reported this week in The American Journal of Psychiatry. Though the study doesn’t prove definitively that ketamine acts on the opioid system, it does complicate the previously held theory that the drug affects the brain’s glutamate system, which handles learning and memory.
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