Tamoxifen is the world's best-selling drug for breast cancer. It's also used to treat infertility, it's given to men with gynecomastia (enlarged breasts), while bodybuilders take it in order to prevent the problem.
Now it's being given to patients to treat their bipolar disorder (manic depression). It has been tested on a group of 66 bipolar patients, half of whom were given a placebo. At the end of a 21-day trial, those in the tamoxifen group reported far fewer attacks.
(Source: Archives of General Psychiatry, 2008; 65: 255-63)