When Botox exploded as a cultural phenomenon in the 90s as a wrinkle smoother, other—and arguably greater—medical Botox uses were also being discovered. Some of the lesser known are Botox treatment for chronic migraines and bladder incontinence, spastic bowel, dystonia, autonomic disorders, chronic pain and certain types of eye disorders. Now, extensive research shows Botox helps people with major depressive disorder feel better.

In 2014, Dr. Norman Rosenthal, clinical professor of psychiatry at Georgetown University School of Medicine who first described seasonal affective disorder, published a double-blind randomized study. In this study of 74 subjects diagnosed with major depressive disorder, the results showed that Botox injected into two eyebrow frown muscles (the corrugator and procerus muscles) subjects showed a 50 percent or greater reduction in depression rating scale scores six weeks following the injection. Many more Botox studies have been published in peer reviews dating back to 2006 with positive outcomes for depressed patients treated with Botox.

The answer may date back to the 19th century when Charles Darwin described what was subsequently called the “omega sign” of melancholy, today’s equivalent of the cosmetic “11’s lines” heard on Botox television commercials. The Darwin-described grief muscles contract when crying and they maintain micro-tension even when the depressed person doesn’t appear to be frowning. When Botox is injected into these two grief muscles, they lose their ability to contract reliably and predictably within two weeks of treatment.

The significance of this was first proposed by Charles Darwin and elaborated by William James in the facial feedback theory that suggests that an individual’s experience of emotion is influenced by feedback from their facial movements. That is, the outward expression of an emotion intensifies it. By extension, therapeutic Botox that weakens frown muscles creates a “fake it until you make it” scenario.

Nina Bull, an underappreciated figure in the history of body psychotherapy, was a pioneer in the mind-body relationship, emphasizing the role of the musculature in subjective experience. She explains, “Preparation for an action precedes, not follows, the subjective awareness of emotion.” In other words, when a depressed person’s frown makes ready for emotional sadness, the body keeps the score.

Another reason for Botox’s anti-depressive effects is rooted in social feedback theory since the world responds more positively to a happier face than a sad face. With Botox-weakened frown muscles, the feedback loop is rendered more positive. It is possible that after Botox treatments, people feel less sad because the people around them respond more positively to them.

Botox has been sensationalized as a cosmetic intervention for the youth obsessed while its significant medical uses remain largely unknown in the lay population. Tillman Kruger, a psychiatrist at Hannover Medical School who did a metanalysis of Botox for depression, explains, “When the brain recognizes something emotional happening in the body, the emotion behind it gets enriched.” Blocking frowning with Botox breaks that feedback loop.