Many supplements attempt to increase testosterone levels, altohugh anything that markedly increases testosterone is a drug and is a controlled substance! However if you have male patern baldness and will go bald eventually no matter what, anything that increases testosterone levels MAY hasten the inevitable hair loss (as can stress, poor diet, etc.), since it is testosterone that triggers the hair folicules associated with male pattern baldness to stop growing hair. Propecia and some other hair loss prevention drugs work by reducing testosterone levels, with various side effects that go along with reduced testosterone levels (diminished libido, etc.). Creatine and most other supplements have no effect on hair loss at all. I knew some people back in colledge who abused anabolic steriods who not only lost all the hair on top of their heads, but also lost their eyebrows! Yet another reason to avoid anabolic steriods, not the least of which is they are illegal, destroy your kidneys, liver and heart, etc.
