Protein Kinase C (PKC) is a family of enzymes that can affect neurotransmitters in the brain. Abnormalities in PKC activity have been linked to bipolar disorder. The breast cancer drug tamoxifen inhibits PKC and a team of researchers in Turkey studied its effect on patients suffering from mania. 50 people participated in the trial in which 29 of them received tamoxifen and 21 a placebo. Neither the patients nor their doctors knew whether they were taking the tamoxifen or the placebo. The study found that tamoxifen was effective in reducing mania and had very few side effects.
Yildiz, Aysegul ... [et al] - Protein Kinase C inhibition in the treatment of mania: a double-blind placebo-controlled trial of tamoxifen Archives of General Psychiatry March 2008, 65(3), 255-263