A pretty good home brewed drug is "ice", much beloved by knees. I take a bigger-than-bathroom sized dixie cup, fill it with water and freeze it. After a strenuous ride and while eating and drinking, I like to spend about 10 mins massaging my knee with a cup of ice. Simply tear the cup away to expose the ice but leave enough to grip with, and rub it around your knee. It will melt but there's plenty for up to 15 mins even. Just keep it moving in order to not "burn" the skin. Good old refreshing blood will come pumping through to help those tissue recover. A towel under the knee is a good idea. Things feel pretty refreshed afterwards.

Obviously, if you have a damaged knee you need stronger measures and tactics.