I am a 46 year-old male and a loyal reader of your blog. Based upon the positive results you have seen with Propecia, I decided to try it, after consulting with a hair-loss surgeon. I have taken 4 pills thus far. I was more than willing to tolerate the side effects reported by Merck if it meant stopping my hair loss. However, I have began to experience possible side effects not reported by Merck, including difficulty sleeping, mental fogginess, breaking out in sweats, along with the more common side effects of decreased energy and drive.
After experiencing these, I began doing some research and ran across sites you may be familiar with, such as Propeciahelp, on which users complain of side effects such as these along with others (e.g., hypogonadism) even after stopping the drug. There are various reports that the drug alters the brain (e.g., mood and thinking) by affecting neurosteroids and can permanently alter the neuroendocrine system.
Obviously, I am freaked out about this and will probably stop taking the drug. I would like to know your opinion on the reports of these side effects, the possibility of permanent alterations of various bodily systems with use of this drug, and your opinion on websites such as these (Propeciahelp) in general. Thank you for your trusted advice.

Suggestions can produce side effects (see “placebo effect” and “power of suggestion”). Your gonads will not shrink in a few days. It is possible (albeit very remote) that there are brain effects, but you should discuss this with your physician and that is why a doctor’s prescription is required for this drug in the United States and many countries. Have an open line of communication with your doctor. If you’re unable to sleep and you think it is related to the drug, talk to your doctor about stopping it.
While forums can be helpful, one must remember that many times they are full of unverified claims and feed into irrational fears. I’ve written about this before here.