I know it's not a scientific study and only a sample size of 2 but i've been on 1mg branded propecia for almost a year and my brother has been on for 4 years (i'm late almost 27 and he is almost 30) and neither of us have had any side-effects to report. I do believe sides effects from finasteride exist but the scientific evidence (not just from merck, but independent studies) have suggested finasteride is safe in the majority of people who take it, unfortunately for some it is not, like all meds, they are not one size fits all.
Also the list of side effects is not a good thing to quote, take a look at these lists:
1) Common adverse drugs reactions associated with use of the ******** include diarrhoea, hypersensitivity, nausea, rash, neurotoxicity, urticaria, superinfection (including candidiasis), fever, vomiting, erythema, dermatitis, angioedema, seizures and pseudomembranous colitis
or how about this one?
2) Insomnia, Headache, Nausea, Diarrhoea, Fatigue, Dry mouth, Anxiety, nervousness and restlessness, Feeling jittery, Decreased sex drive, Problems with getting an erection or ejaculation, Abnormal dreams, Dizziness, Change in taste, Feeling sleepy or lethargic, Blurred vision, palpitations, Flushing, Yawning, Indigestion, Vomiting, Increased sweating, Rash or itching, Frequent urination, Aching joints, Decreased appetite and weight loss, Problems with co-ordination or balance, Tremor or twitching, Dilated pupils, Low blood pressure, Hair loss, Increased tendency to bruise, Feeling hot, cold or generally unwell, Problems with orgasm, Convulsions, Mania, Hallucinations, Panic attacks, Abnormal reaction of the skin to light (photosensitivity), Milky secretion from the breasts (galactorrhoea), Difficulty passing urine, akathisia.
The first one is paracetamol and the second is fluoxetine, better known as prozac. I've prescribed both these medications (i'm a doctor) and would not hesitate to do so again if needed, it doesn't mean that they can be given out like sweets and some people can't tolerate them, but for the vast majority they work, with zero or few sides and help so much that they are life-changing. Finasteride is just like those drugs, it really does change peoples lives, especially for those who can become clinically depressed by baldness, and it doesn't just work for baldness but also for BPH, those patients have been taking 5mg for almost two decades now with few side effects (if any). Everyone has to be vigilant when taking finasteride and to the OP, do your research before starting but also trust your own body, if you feel something is wrong don't keep taking the drug but the statistics would suggest you are far more likely to experience no (or few) sides.
OP, if your interested (and don't get to bored!), i started my own thread in the tell your story section and i did a lot of research into finasteride and have quoted numerous scientific studies on everything from the neurological effect of DHT to the effect of DHT on sperm production. I've tried to be as impartial as possible and have posted not just the positive studies but also the negative ones so you get a clear picture, if you have the time check it out and maybe it will answer a few questions you have.