Propiram is an orally administered analgesic with partial morphine-like agonist and weak antagonist properties.

• Analgesic efficacy of propiram, usually 50 or 100mg, appears comparable to that of standard dosages of other oral opioid drugs [i.e. pentazocine, pethidine (meperidine)] in patients with acute pain of moderate to severe intensity arising from various gynaecological and surgical procedures
• May be superior to codeine in gynaecological and postoperative dental pain.
• Propiram is a non-addictive analgesic for the relief of moderate-to-severe pain.
• Propiram is a partial opioid mu receptor agonist.

Propiram reached Phase III clinical trials in the United States and Canada, but was discontinued.

Propiram:
https://drugs.ncats.io/drug/WT6247U6PX

(1999 Article)
Propiram has had a long and convoluted route through to development, having originally been discovered in the 1970s by Bayer. It was taken right through to the registration stage by Bayer and partner Schering-Plough in their ill-fated joint venture in the mid-1980s, but once this was dissolved the rights transferred to S-P, which considered propiram maverick to the rest of its portfolio and killed the project, even though approvals had been granted in some European countries. Roberts acquired the product in the late-1980s, but it languished in the pipeline until a review a couple of years ago drew attention to its potential in the $3.5 billion US opioid analgesia market.

Roberts' propiram betters tramadol in Phase III:
https://www.thepharmaletter.com/article/roberts-propiram-betters-tramadol-in-phase-iii

• A partial mu opioid receptor agonist and weak mu antagonist analgesic. It exhibits weak opioid antagonist activity on the mu receptor - quite a bit weaker than its agonist effects.
• Related to other drugs such as phenampromide and diampromide
• Invented in 1963 in the United Kingdom by Bayer

  It was not widely marketed, although it saw some limited clinical use, especially in dentistry.

• 10% of the analgesic potency of morphine
• 50 mg of propiram is equivalent to about 60 mg of codeine or 50 mg of pentazocine
• A duration of action of 3 to 6 hours
• Side effects include sedation, dizziness, nausea and vomiting.

Propiram has been available in oral, rectal, and injectable formulations, with bioavailability above 97% after oral administration.