Does PRP actually work for hair loss?

Thank you for this great question.
As far as PRP and hair restoration, it works best when used in conjunction with a hair transplant. A good way to think about it is as a better fertilizer for the implanted hair follicles, improving survival, growth and density of the transplanted hair. As an isolated intervention, it has definitely shown in numerous high-quality studies to have a positive effect on the number of hairs and thickness of hairs in the treated regions compared to control, with most patients noting an improvement. However, the degree of improvement is limited. The concentration of the platelets in the PRP is something that has been studied extensively as well, and it has been shown that between 1-1.5 million platelets/uL is ideal for the purpose of hair restoration. This is anywhere between 4-7x concentration of platelets in our blood. Concentrations higher than 1.5 million platelets/uL are actually detrimental to the hair growth process. Many practitioners who offer PRP for hair restoration will have concentrations of 2-3x normal, which is certainly better than nothing but may not give maximal efficacy. Typically, you get 3-4 treatments every 4 weeks, then annually, as the effects of the PRP are generally lost by 12 months.
Topical Minoxidil (Rogaine) and oral Finasteride (Propecia) are still the mainstays for non-surgical hair restoration, and if you've already started using them, make sure to keep it up. Given the safety profile of PRP, it may be a good alternative for patients who have had little success with Minoxidil and Finasteride or cannot tolerate the associated side effects. Laser caps have also shown some promising results in slowing down hair loss, but again, typically used as an adjunctive (add-on) intervention.   
Ultimately, if you are able to afford it, are motivated and are getting increasingly concerned with your hair loss, I'd recommend visiting a hair restoration specialist to talk about a hair transplant as it is the only way to actually add new hair to the balding scalp. Hope that helped! Best, Dr. Roy.

PRP is a restorative regenerative treatment that improves the tissue it is injected into.  In the hair restoration field, it shows great improvement in healing post procedure and can also be used annually (depending on the method used) to reverse the aging process of follicles.