A common complaint about wrinkle-masking Botox is that recipients have difficulty displaying emotions on their faces. That side effect might be a good thing, however, for people with treatment-resistant depression.

In the first randomized, controlled study on the effect of botulinum toxin—known commercially as Botox—on depression, researchers investigated whether it might aid patients with major depressive disorder who had not responded to antidepressant medications. Participants in the treatment group were given a single dose (consisting of five injections) of botulinum toxin in the area of the face between and just above the eyebrows, whereas the control group was given placebo injections. Depressive symptoms in the treatment group decreased 47 percent after six weeks, an improvement that remained through the 16-week study period. The placebo group had a 9 percent reduction in symptoms. The findings appeared in May in the Journal of Psychiatric Research.

Study author M. Axel Wollmer, a psychiatrist at the University of Basel in Switzerland, believes the treatment “interrupts feedback from the facial musculature to the brain, which may be involved in the development and maintenance of negative emotions.” Past studies have shown that Botox impairs people's ability to identify others' feelings, and the new finding adds more evidence: the muscles of the face are instrumental for identifying and experiencing emotions, not just communicating them.