Metopon was developed as an analgesic opium derivative. This drug has a high affinity to the mu-opioid receptor and produces antinociception through this receptor. Metopon was available in Canada only in tablet form for oral administration; however, because of the drug addiction, the Drug Addiction Committee recommended its limited use.

Metopon Hydrochloride:
https://drugs.ncats.io/substance/6O34Q1K8M6

Metopon:
The second precedent involved the semi-synthetic opioid Metopon discovered during World War II by pharmacologists working for the U.S. National Research Council. Since the 1920s, opioids had been much more strongly regulated than other pharmaceuticals to protect consumers. As I explain in my upcoming book "White Market Drugs," they could only be sold by a licensed pharmacist on a physician's prescription. For decades, the Federal Bureau of Narcotics, working with National Research Council pharmacologists, imposed tight restrictions on the development and marketing of new opioids.

It was a daily battle for these government agencies to identify and then counteract what they considered to be dangerous marketing hype by drug companies pushing the latest miracle opioid.

So, daringly, in 1946, the two agencies hatched a radical idea: They would take out a patent on Metopon and market it themselves. Instead of trying to achieve maximum profit, they would only serve public health. They would not advertise Metopon at all. Instead physicians would learn about it through sober, informative pronouncements from experts in medical journals. Moreover, sales would initially be restricted to patients suffering from end-stage cancer. The government believed Metopon would win out over competitors not because of marketing hype but because it was actually superior. But it didn't work out that way. Sales were sluggish after Metopon's launch in 1947, and remained low even after the authorities allowed sales for more types of pain. Even Harry Anslinger, head of the Federal Bureau of Narcotics and an otherwise ferocious critic of pharmaceutical opioid advertising, complained about lackluster marketing. While it remained technically available, Metopon never earned more than a minute fraction of the U.S. opioid market.

Purdue Pharma Metopon:
https://theconversation.com/the-company-that-makes-oxycontin-could-become-a-public-trust-what-would-that-mean-126981

invented in 1929 as an analgesic. longer acting than hydromorphone, Metopon is less potent and its oral bioavailability is fairly low. Generally, Metopon has few advantages to distinguish it from other, more commonly used opioid analgesics, although it does have a slightly lower tendency to produce nausea and respiratory depression compared to morphine. It did see some use in medicine - oncology in particular - in the US in the 1950s. Currently metopon, which has a DEA ACSCN of 9260, does not have an annual manufacturing quota listed in the Federal Register and the bulk of the research on the drug at this time is taking place in Germany, Switzerland, and Austria.