Orphenadrine (Norflex, Mephenamin, Disipal, Banflex, Flexon, Biorphen, Brocasipal, and others) is a drug used to treat pain, muscle spasm and other symptoms of injury and other problems. It is also used for treating some aspects of Parkinson's Disease.

Orphenadrine works by reducing muscle spasm and pain of varying aetiologies and types, viz., acute pain of injury and other causes as well as chronic and recurring acute pain syndromes producing nociceptive and/or neuropathic pain. It can be used as the main analgesic/muscle relaxant in cases of, for example, sports injuries, or as an atypical (adjuvant) analgesic and/or adjunct to typical analgesics such as opioids and Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and for reduction of some histamine-related side effects of opioids, especially codeine and its semi-synthetic derivatives.

Orphenadrine is an anticholinergic and an NMDA receptor antagonist [http://www.neurotransmitter.net/muscle_drug_reference.html]drug belonging to the ethanolamine family of antihistamines.

Chemically, orphenadrine is a methylated derivative of diphenhydramine (Benadryl, Sominex, Nytol etc). It is produced by reacting dimethylaminoethanol with 2-methylbenzhydryl chloride. The free base has a molecular weight of 269,38 and an empirical formula of C18H23NO. The molecular weight of orphenadrine hydrochloride is 305,85, and 461,50 for the citrate.

This drug was first synthesised in the late 1940s in Europe and patented in the United States by Parke-Davis in July 1951. Currently, orphenadrine preparations are made in the United States and Canada by Parke-Davis and other companies including 3M. In addition to muscle-relaxant and antihistaminic effects, orphenadrine has significant antispasmodic, direct analgesic, and weak to moderate local anaesthetic actions. It also produces drowsiness and can have mild sedative and anxiolytic effects.