Spironolactone can cause gastrointestinal problems fairly often. Since it also affects steroid receptors elsewhere in the body, it can cause gynecomastia, menstrual irregularities and testicular atrophy. Other side effects include ataxia, impotence, drowsiness and rashes. A carcinogenic effect has been demonstrated in rats. [2]
http://en.wikipedia.org/wiki/Spironolactone
Is it really that good for receeding hairlines and worth of risk?