Flupirtine is a centrally acting K+ channel opener with weak NMDA antagonist properties.[13] It is used in Europe for moderate to strong pain and migraine and its muscle-relaxant properties. It has no anticholinergic properties and is believed to be devoid of any activity on dopamine, serotonin, or histamine receptors. It is not addictive, and tolerance usually does not develop.[14] However, tolerance may develop in single cases.[15]