PROBLEM TO BE SOLVED: To provide a form allowing controlled-release of 3-(3-dimethylamino-1-ethyl-2-methyl-propyl)-phenol compound and suitable for administration for the medical treatment of sharp pain.SOLUTION: The compound is a salt or co-crystal of (a constituent a) 3-(3-dimethylamino-1-ethyl-2-methyl-propyl)-phenol and (a constituent b1) at least one kind of acid selected from embonic acid, dibenzoyl tartaric acid, etc., or (a constituent b2) at least one kind of acid selected from nicotinic acid, etc., (where, the salt or co-crystal of the constituent (a) and the constituent (b2) exists in a crystalline form and/or an amorphous form).SELECTED DRAWING: None
