Despite effective pharmacological and psychotherapeutic treatment options for depression, about one third of patients affected by depression prove resistant to therapy. The injection of botulinum toxin A (BTA) into the glabellar muscles of the forehead constitutes a new approach to treating depression. Such treatment exhibits relatively significant effectiveness and demonstrates considerably different properties than conventional antidepressants. BTA injections into the glabella are associated with an antidepressant effect lasting several months, which sets them apart from other pharmacological antidepressant interventions thus far. The local injection of BTA entails no expected pharmacological interactions with other medications. Such properties may make BTA injections a potentially cost-effective alternative to standard antidepressant treatments, exhibiting only very few undesirable events. Three randomized, placebo-controlled clinical studies have demonstrated the effectiveness of BTA treatment for patients affected by unipolar depressive disorder. Studies conducted to date display a few methodological weaknesses. The sample size in the individual studies tended to be small, with blinding methods for BTA treatment being not ideal. Currently, several hypotheses are under discussion concerning the mechanism of action of BTA treatment, namely the information-processing hypothesis, the aesthetic hypothesis, as well as the social hypothesis.
