There are four categories of creams that are deigned to decrease pain when rubbed into the muscles or joints.
1. COUNTERIRRITANTS: The goal of these creams is to distract your mind from the pain by irritating the surrounding nerve endings. The main ingredients are menthol, camphor or eucalyptus oil. Example of these creams would be Ben-Gay, IcyHot or Therapeutic Mineral Ice.
2. SALICYLATES: These creams have the main ingredient of salicylate ( similar to aspirin ). They may decrease joint inflammation especially when used on joints that are close to the skin: fingers, knees and elbows. Examples are Aspercreme or Myoflex.
3. CAPSAICIN: Capsaicin is found in cayenne peppers and it works to decrease pain by decreasing the amount of substance P. Substance P is a neurotransmitter that is believed to send pain messages to the brain. The theory is, if you decrease substance P, you will decrease pain. Examples are Zostrix, Capzasin-P
4. NSAIDS: The active ingredient is diclofenac sodium which is a non-steroidal anti-inflammatory drug (NSAID). The creams are designed to block the production of prostaglandins. Prostaglandins increase inflammation in joints. Examples are Pennsaid and Voltaren Gel. These creams are only available with a prescription.
This information was taken from a blurb in the Arthritis Today 2012 Drug Guide.