On his latest trip to Germany, Kobe Bryant made national news when he checked in to get a Platelet-Rich Plasma (PRP) treatment, a controversial therapy that processes the patient's blood to speed up the healing process. But it wasn't his first time undergoing this rehab method, nor was he the first athlete to try it. Like Tiger Woods, who used the treatment in 2010 to overcome knee troubles, the aging Laker has used the injections to help heal ankle and knee injuries suffered last season. But just how effective is the treatment?

For now, this question is still a point of controversy. "We're just beginning to understand how, when, and for whom PRP will work," says Dr. Allan Mishra, a physician and researcher at California's Menlo Medical Clinic. "But I think we're at the precipice of a new way of treating injuries."

There are many variations, but, in general, the procedure begins with drawing two to three tablespoons of the patient's blood and placing it in a centrifuge for 10 to 15 minutes. The spinning separates the blood into three components: red blood cells, plasma, and a mix of platelets and white blood cells. The platelets and white blood cells are then injected into the injured area.

In the 'British Journal of Sports Medicine,' Dr. Leon Creaney, a physician and sports medicine consultant, compares platelets to a construction site foreman. After a cut or injury, the platelets inform the body of the problem and request specialized workers to fix the damage. The theory with PRP is that by injecting platelets into an injured area, they will kick-start the healing process.

Clinical results are mixed. For instance, a just released study of people with rotator-cuff injuries found PRP reduced the chances of reinjury from 56 percent to 20 percent. But another study found that PRP had no effect on rotator cuff injuries. The treatment seems to be most effective on chronic tendinitis and knee osteoarthritis, says Mishra.

Everyone in the field seems to agree on two things: More research is needed, and side effects are minimal. PRP was removed from the World Anti-Doping Agency's list of banned methods in 2011 and an analysis of 800 patients who received PRP for various reasons found no adverse side effects.

"The treatment is not transformative, and it doesn't work the same on everyone," says Mishra. "My advice is for people to reserve PRP until all other treatment options have been exhausted and they are considering surgery."