I've been a finasteride user for 6 of the last 7 years. I only recently switched from brand name (propecia) to generic brand. I get it through pharmacy and have a doctors prescription. The generic is about 2/3 the cost for me compared to brand name propecia.
Three years ago I took one year off (along with stopping nizoral and rogaine foam) and lost a lot of ground. I wish I hadn't stopped but I know I can't change that now. I'm happy with what hair I have given many 30 year old guys are bald. Hell, many guys bald hard in early 20s. In the two or so years since restarting, I have better hair coverage. Not crazy regrowth, but definitely noticeable and worth the cost (in my view).
If you're considering using them, you may find hair loss forums. The so-called 'big 3' in the fight are finasteride (propecia), minoxidil (the key ingredient in rogaine) and nizoral (special anti-fungal shampoo). I use all three together. Many people advocate using all three as they help fight hair loss in different ways and the sum of them is either stopping your hair loss or greatly slowing it down.
I have had no bad sides to my knowledge thus far. Occasionally I would feel light headed after applying rogaine foam early on seemingly when I had a strong black coffee (maybe I am imagining things, but seemed to go hand in hand !) but that was for a few fleeting moments.
Good luck whatever you decide. MPB can be a total kick in the nuts.