If you are going to start on Propecia you should commit to annual blood tests to make sure all of your levels are within the safe range. Tell the doctor what you take so that he can add testing as needed. Some of these drugs mask potential problems (prostate cancer etc.) so your doctor needs a heads-up to look for those.
You should read the manufacturers warnings carefully so that you know what you are getting into, they all have in-depth study results that go far beyond the marketing hype you see on TV or on the front page of their web sites.
And, make sure you understand that the effects of the drugs only last as long as you take them. You're locked in for life, once you stop taking them you lose everything that you would have lost without the drugs, and it usually happens quickly. If you have to stop taking them due to some kind of medical or physical reason, everything will be lost and you can't get it back. Also, some patients become immune to the benefits after 5 years, which means they either need to find a new drug or they will lose the hair.
If you bank on the meds as part of your HT strategy, it will mean more work later if you stop the meds or become immune to them. For example, some doctors don't touch the crown if you say you are going to start meds.
I'm not against anyone taking meds, they have their place and have benefited lots of people. I just wanted to share a slightly different view on them after I researched them.