Tennis elbow (lateral epicondylitis) is a frequent cause of elbow pain. Repetitive use of the arm, especially repeated extension of the wrist and elbow, causes strain and inflammation of muscles and tendons. These movements are common in many activities besides tennis. Commonly used treatments include nonsteroidal anti-inflammatory drugs, physical therapy, corticosteroid injections, and surgery. Researchers do not know if any of these therapies are really effective because tennis elbow eventually improves by itself. Botulinum toxin (which is often referred to by one of its brand names, “Botox”) is another potential treatment. Botulinum toxin is a protein produced by bacteria that blocks conduction of nerve impulses. It may reduce pain by blocking the nerve impulses that cause painful muscle spasms. Small studies suggest that botulinum toxin is an effective treatment for tennis elbow, but the studies are not definitive.