For hair loss prevention, some good anecdotal reports have been made with taking 100 mg of zinc gluconate at bedtime. However, it might be a good idea to take B6 with it also, since some sources say B6 is required to activate it. However, B6 by itself may actually inhibit 5-AR--which saw palmetto also has been reported to do. (Apparently Dan Duchaine reported that a self-test can be done by shaving a spot of hair on your arm and comparing...I don't know about that, I haven't see that quote personally...however, taking saw palmetto you PROBABLY should feel like you are sweating a little more than normal...if it interrupts DHT by way of 5-AR then it will definitely have an indirect impact on prolactin levels...thus the sweating slight increase. This is just my reasoning however, and could be off base).
Also know that some people combine the herbs Saw Palmetto, Fo-ti, Zinc and a good B-complex that contains B6 to stop hair loss.
Hope that helps.