The present invention discloses a 3-[3-(dimethylamino)-1-ethyl-2-methylpropyl]phenol resin complex, preferably an amorphous 3-[3-(dimethylamino)-1-ethyl-2-methylpropyl]phenol resin complex formed by the reaction between a cation exchange resin and 3-[3-(dimethylamino)-1-ethyl-2-methylpropyl]phenol or a pharmaceutically acceptable acid addition salt thereof. It can exhibit an in-vitro release rate of 3-[3-(dimethylamino)-1-ethyl-2-methylpropyl]phenol from the 3-[3-(dimethylamino)-1-ethyl-2-methylpropyl]phenol resin complex which is in accordance with the requirements of Ph. Eur. on “conventional-release dosage forms”.
