I haven't decided if I want to call bullshit right away or drag you through this long drawn out post where I end up saying...Bullshit! Oops, there it went. Let's get some things straight, the Internet is full of people eager to sell you anything you are willing to buy and don't get me wrong I obviously want to sell you something but I'm not going to sell you crap. I'm going to educate you on things that work and do my favorite thing, calling out everyone else who just try's to sell you some affiliate crap product.
There is a thing layer of truth for these marketing scammers to stand on but it's real thin. Biotin has been marketed for years to women because it has been linked to strengthening keratin levels in your body. Keratin by the way is a protein that is the building block for all skin, hair and nails. So the next question is, does it even work at all? The answer is yes it does BUT only if you have a deficiency. Remember people a supplement is just that, it "supplements" in an area you have a deficiency. If your biotin levels are in check then you're not going to notice any change but don't tell that to your girlfriend because she probably swears by it.
This is how much of a crock this supplement is, take a guess what the recommended dosage is, go ahead I'll wait... You guessed it, there isn't one. Now common sense would tell you that if it was that important then it would have a recommended dosage attached to it so it obviously ranks nice and low on the list. You will find a lot of people say that 2.5mg is the best dosage to take for optimal effects but this is really just them shooting in the dark, there is no scientific evidence to support that, it's a case of broad (opposite of bro) science.
Moral of the story, go out there and spend/waste all your money on products that aren't going to work or buy something that has actual social & clinical proof like a rogaine product.