What is the best medicine to cure shoulder tendonitis?

Inflammation: Overuse injuries respond best with rest, ice and nsaids. Therapy helps with strengthening and range of motion. If things are not improving consider a cortisone injection.

Possibly: PRP is an offered treatment that has shown good success however is considered experimental at this time. The basic theory is it helps to strengthen the ligaments using your own platelets/growth factors and therefore reducing stress on the joint by tightening them up. As far as I know its safer than steroid injection. Pretty cool stuff. Check out Regenexx.Com.