This thesis addresses the antidepressant effect of Ketamine, Botulinum toxin, and Psilocybin on patients suffering from major depressive disorder or depressive symptoms of bipolar disorder. The results are compared to a placebo and then the usual antidepressants. As a conclusion Ketamine can be recommended as an antidepressant when other methods have been unsuccessful. Botulinum toxin can also been recommended when other treatments have failed. But Psilocybin can not be recommended since it has not been studied enough.