Etorphine was the first potent opiate agonist employed primarily for use in non-domestic and wild species. Etorphine was 500 times as potent as morphine, with a very rapid onset and short duration of action. In morphine-dependent subjects, etorphine suppressed abstinence but for a shorter period than morphine. Etorphine is a full opiate agonist and binds to multiple opiate sites in the central nervous system. It is believed to produce its clinical effects through binding the µ-, δ-, and κ- opiate sites. It has a potent effect on depressing the respiratory centers of the CNS thus resulting in apnea being commonly seen in immobilized animals. Etorphine revolutionized the ability of biologists and veterinarians to safely capture and restrain many species that previously could not be handled. Etorphine is not currently commercially available due to lack of production by the manufacturer.

Norcodeine is the N-demethylated derivative of codeine. It has relatively little opioid activity in its own right, but is formed as a metabolite of codeine following ingestion. Codeine and its other major metabolites codeine-6-glucuronide and norcodeine have weak affinity to opioid μ-receptors.

Desomorphine is the common name for 4,5--epoxy-17- methylmorphinan-3-ol or dihydrodesoxymorphine-D. It is an opioid analogue and morphine derivative in which the 6-hydroxyl group and the double bond at carbons 7 and 8 of morphine are reduced. Desomorphine can cross the blood–brain barrier, binding to opioid receptors, similar to the pharmacokinetic distribution of all phenanthrene-structured alkaloids. Taking Desomorphine causes euphoria as well as sedative and analgesic relief. In addition to its faster onset than other powerful painkillers drugs such as morphine, desomorphine also initiates less sedative effects and seems to have favorable postoperative results, such as reduced need for catheterization, less dizziness, and decreased vomiting incidence. In comparison with Morphine, Desomorphine is faster reduced. It follows that it has to be taken it more frequently to get the same effects. Furthermore, it causes side effects such as respiratory and gastrointestinal problems and increased blood pressure. In addition, Desomorphine’s withdrawal symptoms are up to three times longer than Morphine’s. This leads to the conclusion that Desomorphine is more addictive. At present, desomorphine is classified as a narcotic drug (DEA code number 9055) in Schedule I of the U.S. Controlled Substances Act and is listed as a controlled substance under the international Single Convention on Narcotic Drugs of 1961.

Nicodicodine is a cough suppressant and analgesic. It was first synthesized in 1904. It is a Schedule III drug. Nicodicodine is metabolised in the liver to dihydromorphine. Since the final active metabolite is the slightly stronger opiate than morphine, nicodicodine can be expected to be more potent and longer acting than nicocodeine.