The present invention relates to an agent for prevention, treatment or inhibition of symptom progression of a pain and/or for control of an analgesic comprising (2R)-2-propyloctanoic acid, a salt thereof or a prodrug thereof, in which an amount per dose is from 1 mg to 5000 mg (preferably from 10 mg to 5000 mg). By administering (2R)-2-propyloctanoic acid, a salt thereof or a prodrug thereof in an amount per dose within the range as described above, a pain, in particular, a neurogenic pain associated with a disease such as cancer pain, postherpetic pain, diabetic pain, HIV-associated neurogenic pain, calculus-induced pain, neuralgia, orofacial pain or hyperalgesia can be remarkably relieved. Moreover, undesirable effects on the living body relating to the use of an analgesic can be relieved.