Is Stem Cell Hair Loss Treatment Effective?

How "effective" a treatment may be depends on your understanding of the treatment limitation and clear goals.  There is no "cure" for genetic balding so you have to set your goals accordingly.

Stem cell treatment for hair loss? You can check with the FDA but I do not think that this is approved to grow hair. Put your money to better use elsewhere.

It is difficult to answer your concern without more information.  If you still have active hair follicles, in large quantity, which it sounds like you do, the expectation is that you would start seeing some improvement from PRP (if that is the treatment you had) after several months to a year.  Are you massaging your scalp, taking a hair vitamin regimen, eating healthy, including avocadoes in your diet, adding Rogaine? All these things may enhance results too.  Do you have some follow-up on how you are doing now? Since PRP is a blood product, it does not fall under the jurisdiction of the Food and Drug Administration (FDA).

Stem cell therapy is not approved as a hair loss treatment yet so check with your clinic what treatment you are receiving and the exact name of it.  It may be mesotherapy or platelet rich plasma or other supportive therapies but it is unlikely that it is "stem cell therapy". If it was, you would be part of a formal clinical trial and you would be informed you were part of a research study.