AD-1211 is an opioid

Opioid

An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

 analgesic

Analgesic

An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....

 drug invented in the 1970s by Dainippon Pharmaceutical Co. It is chemically a 1-substituted-4-prenyl-piperazine

Piperazine

Piperazine is an organic compound that consists of a six-membered ring containing two opposing nitrogen atoms. Piperazine exists as small alkaline deliquescent crystals with a saline taste....

 derivative, which is structurally unrelated to most other opioid drugs. The (S) enantiomers in this series are more active as opioid agonists, but the less active (R) enantiomer of this compound, AD-1211, is a mixed agonist-antagonist at opioid receptors with a similar pharmacological profile to pentazocine

Pentazocine

Pentazocine is a synthetically prepared prototypical mixed agonist-antagonist narcotic drug of the benzomorphan class of opioids used to treat moderate to moderately severe pain...

, and has atypical opioid effects with little development of tolerance or dependence seen after extended administration in animal studies.