Wikipedia
Methopholine is an opioid analgesic drug discovered in the 1950s by a team of Swiss researchers at Hoffmann-La Roche. Methopholine is an isoquinoline derivative which is not structurally related to most other opioids. However, its structural similarity to papaverine is notable.
It has around the same efficacy as an analgesic as codeine, and was evaluated for the treatment of postoperative pain. Methopholine tablets were marketed in the United States under the brand name of Versidyne, but the drug was withdrawn from the market in 1965 due to the occurrence of ophthalmic side-effects and the discovery that it could produce corneal opacities in dogs.
Methopholine has two enantiomers, with the levo (R) enantiomer being the active form, around 3x the potency of codeine, and the (S) enantiomer being inactive.
Analogues where the 4'-chloro group has been replaced by other groups have also been tested, the fluoro derivative being slightly more potent than chloro, and the nitro derivative being most potent of all, with the racemic 4'-nitromethopholine being around 20x the potency of codeine.