Magnesium salicylate tetrahydrate is an aspirin-like drug used to relieve mild to moderate pain. It may be used particularly to treat the pain and swelling caused by osteoarthritis and rheumatoid arthritis. This drug is available in various strengths, both as a prescription and over-the-counter medication. The brand names this drug may be found under include: Novasal, Doan's Regular, Doan's Extra Strength, Momentum, Keygesic-10, and MST 600. It may also be available under other brand names not listed here.