Saw palmetto supplements( which they claim have no side effects) work on the same principle as other 5-AR inhibitors such as propecia and avodart. These medicines suppress 5-Alpha reductase enzyme which converts testosterone to DHT. And, DHT, is not just another by-product of the conversion, its the hormone which makes a man, a man.
Taking any hormonal modulator( herbal or non-herbal) can cause many unwanted side effects. Saw Palmetto has been known to cause problems such as gynomastia, loss of libido and impotence. There are numerous people who have taken 5AR inhibitors( Saw Palmetto, Propecia etc) and learnt it the hard way. Before taking these medications, advice of a’real’ doctor should be taken rather than a trichologist.