Pentazocine,[3] sold under the brand name Talwin among others, is an analgesic medication used to treat moderate to severe pain.

[4] In the 1970s, recreational drug users discovered that combining pentazocine with tripelennamine (a first-generation ethylenediamine antihistamine most commonly dispensed under the brand names Pelamine and Pyribenzamine) produced a euphoric sensation.

[7][8][9] After health-care professionals and drug-enforcement officials became aware of this scenario, the mu opioid receptor antagonist naloxone was added to oral preparations containing pentazocine to prevent perceived "misuse" via injection,[10] and the reported incidence of its recreational use has declined precipitously since.

In an open-label, add-on, single-day, acute-dose small clinical study, pentazocine was found to rapidly and substantially reduce symptoms of mania in individuals with bipolar disorder that were in the manic phase of the condition.

[11] It was postulated that the efficacy observed was due to κ-opioid receptor activation-mediated amelioration of hyperdopaminergia in the reward pathways.

[12] Pentazocine was developed by the Sterling Drug Company, Sterling-Winthrop Research Institute, of Rensselaer, New York.

It was approved by the Food and Drug Administration in June 1967 after being favorably reviewed following testing on 12,000 patients in the United States.

[citation needed] Pentazocine is still classified in Schedule IV under the Controlled Substances Act in the United States, even with the addition of Naloxone.