Methocarbamol is a central muscle relaxant used to treat skeletal muscle spasms. The mechanism of action of methocarbamol is currently unknown, but may involve the inhibition of carbonic anhydrase.The muscle relaxant effects of methocarbamol are largely attributed to central depressant effects; however, peripheral effects of methocarbamol to prolong muscle refractory period have also been reported.
Potential side-effects include: drowsiness, dizziness, clumsiness (ataxia), upset stomach, flushing, blurred vision, and fever. Both tachycardia (fast heart rate) and bradycardia (slow heart rate) have been reported; these can be serious.
Other serious side-effects include the development of a severe skin rash or itching, fainting, jaundice, persistent nausea/vomiting, stomach/abdominal pain, mental/mood changes, trouble urinating, and signs of infection. If taken in large amounts at once or more than directed or as prescribed, dysphoria or suicidal thoughts may occur. In addition, methocarbamol may cause urine to turn black, blue, or green. However, this effect is harmless.