Nonprescription (over-the-counter) diclofenac topical gel (Voltaren Arthritis Pain) is used to relieve pain from arthritis in certain joints such as those of the knees, ankles, feet, elbows, wrists, and hands. Prescription diclofenac topical solution (Pennsaid) is used to relieve osteoarthritis pain in the knees. Diclofenac is in a class of medications called nonsteroidal anti-inflammatory drugs (NSAIDs). It works by stopping the body's production of a substance that causes pain. Diclofenac is also available as a 3% gel (Solaraze; generic) that is applied to the skin to treat actinic keratosis (flat, scaly growths on the skin caused by too much sun exposure). This monograph only gives information about nonprescription diclofenac topical gel (Voltaren Arthritis Pain) for arthritis and prescription topical solution (Pennsaid) for osteoarthritis of the knee. If you are using diclofenac gel (Solaraze, generic) for actinic keratosis, read the monograph entitled diclofenac topical (actinic keratosis).