Mephenesin is a central muscle relaxant, acting through a depression of the activity of some neurones in the caudate nucleus. It was proposed as a potential treatment of alcohol withdrawal syndrome in the 50s. This over the counter medicine is now mainly prescribed to treat spasticity or as an adjunctive treatment of painful muscle spasm. We know little about this substance except that side effects are venous thrombosis, haemolysis or cutaneous intolerance. Yet, no case of abuse or dependence has been reported.

To report a series of 5 clinical cases in patients who developed abuse or dependence to mephenesin.

We performed a systematic search in data bases of both Paris addictovigilance and poison centres from 1999 to 2010. Clinical details were obtained from clinicians when possible. A literature search was also performed to describe mephenesin mechanisms of actions that could be implied.

Three (3) women et 2 men aged 35 to 52 years (m : 43.6) were identified as abusing mephenesin, among which 4 patients had a full DSM IV criteria of dependence. All had a previous history of abuse or substance dependence (alcohol, heroin, codeine, ketamine…).The average mephenesin daily intake was 13 g (9 to 24 g) when the maximum recommended dosage is 3 gr/d. In one case, a withdrawal syndrome was observed (tremor, aggressiveness).

Mephenesin may be abused by patients with previous risk factors, especially a personal history of alcohol dependence.