Etroside is a combination of two medicines: Etoricoxib and Thiocolchicoside, which relieves pain and relaxes the muscles. Etoricoxib is a non-steroidal anti-inflammatory drug (NSAID) which works by blocking the release of certain chemical messengers that cause pain and inflammation (redness and swelling). Thiocolchicoside is a muscle relaxant. It works on the centers in the brain and spinal cord to relieve muscle stiffness or spasm and to improve pain and movement of muscles.