Admittedly my doubts are solely based on the fact that I see the 5-HTP next to the fish oil pills and other non-FDA approved supplements at the pharmacy. It fits into the profiled of what I consider "alternative medicine," and generally I agree with the idea that if alternative medicine actually worked, it would be called medicine.
You've done more research than me though. I'll defer to your judgment here.
5-HTP and omega 3 fatty acids (fish oil pills) are not "alternative medicine" supplements. They're regular medicine supplements. It's believed most people are probably deficient in omega 3, unless they eat a lot of fish.
In my opinion, the "alternative medicine" label shouldn't be thrown around recklessly at substances that clearly have psychoactive properties and strong theoretical or proven mechanisms of action. They may be insufficiently researched regarding their potential treatment of specific conditions, but you shouldn't throw them in the same boat as homeopathy or acupuncture or reiki.
I think 5-HTP probably isn't a suitable supplement to treat depression in the long term (risk of downregulation and cardiac issues), but it's definitely one form of treatment for many people.
I'm not an alternative medicine fanatic, but neither am I someone who thinks that Big Pharma is nothing but an evil conspiracy, but I suspect at the end of the day, these things don't get a lot of attention because there's no "miracle drug" that can be patented and sold for billions.
They fall outside the jurisdiction of the FDA (whether they should or not is debatable), but I wouldn't write any of these items off just because they are marketed as supplements.
I think the best we can say is that we don't know enough about them and their effects. Look at how often the "eat X, it's good for you"/"don't eat X, it's bad for you"/"X has no significant effect" articles we see... often where X is the same thing in different categories.
It must depend on where you live and what kind of stores sell those supplements around you.
I purchased this bottle of 5-HTP at a pharmacy in the health supplements aisle next to vitamins and other products such as melatonin. At this pharmacy chain, this aisle is as important big and prominent as any regular medecine aisle. If you ask for over the counter medecine, there are chances the pharmacist will refer you to this very aisle (melatonin for sleep, etc.)
You've done more research than me though. I'll defer to your judgment here.