Saw Palmetto extract from the berries of the American dwarf palm has been used for urinary dysfunction caused by enlarged prostrate.
One study showed in reduced the DHT levels in the prostate tissues of subjects. Large controlled studies results have have mixed so far.
This is the same with studies for hair growth using Saw palmetto. With oral supplements, there will be variability of standardised extract between manufacturers which will affect the true strength of the supplement.
Shampoos with saw palmetto will have negligible impact on hair due to low contact time and frequency of application. With oral supplements, side effects reported (although rare) are constipation, decreased libido, diarrhoea, headache, hypertension, nausea, urine retention and pancreatitis.
It has been shown that it may also affect liver enzymes resulting in some medical interactions. One should be careful with blood thinners. The preparation is not recommended during pregnancy and breastfeeding and like Finasteride, can cause effects to the foetus.
Before taking saw palmetto, it is important to firstly seek professional medical advice. Like all herbs, there is always a potential for unwanted interactions with certain medicines.