Morphinone is an oxidation product of morphine with weak agonistic activity toward mu opioid receptor. Morphinone is the intermediate when morphine is being converted to hydromorphone. Morphinone is toxic compound, subcutaneous administration of morphinone produced a reduction of hepatic non-protein sulfhydryl concentration. Glutathione or cysteine significantly decrease Morphinone toxicity.

Oliceridine (TRV-130) is a potent μ-opioid receptor agonist. In cell-based assays, TRV130 elicits robust G protein signaling, with potency and efficacy similar to morphine, but with far less β-arrestin recruitment and receptor internalization. In rodents, TRV130 is potently analgesic while causing less gastrointestinal dysfunction and respiratory suppression than morphine at equianalgesic doses. Oliceridine is being developed by Trevena for the first-line treatment of moderate-to-severe acute postoperative pain. Phase III development is underway for the treatment of postoperative pain in the US. Phase II development is underway for the treatment of acute pain in the US.

Dezocine was discovered and patented by American Home Products Corp. in 1978. Dezocine is a partial opiate drug and was used for pain management under brand name Dalgan. But then usage of this drug was discontinued in US. Dezocine acts as a partial μ-receptor agonist, a κ-receptor antagonist, and a norepinephrine and serotonin reuptake inhibitor (via norepinephrine transporter and serotonin transporter). Dezocine shares the CNS depressant and respiratory depressant effects of opioid analgesics. Dezocine has not been shown to produce clinically significant cardiovascular adverse effects.

Propoxyphene is a centrally acting opiate analgesic. Propoxyphene is an odorless, freely soluble in water, white crystalline powder with a bitter taste. In vitro studies demonstrated propoxyphene and the metabolite norpropoxyphene inhibit sodium channels (local anesthetic effect) with norpropoxyphene being approximately 2 fold more potent than propoxyphene and propoxyphene approximately 10 fold more potent than lidocaine. Propoxyphene and norpropoxyphene inhibit the voltage-gated potassium current carried by cardiac rapidly activating delayed rectifier (hERG) channels with approximately equal potency. It is unclear if the effects on ion channels occur within therapeutic dose range. Propoxyphene is indicated for the relief of mild to moderate pain.

Dihydrocodeine is an opioid analgesic used as an alternative or adjunct to codeine to treat moderate to severe pain, severe dyspnea, and cough. It is semi-synthetic, and was developed in Germany in 1908 during an international search to find a more effective antitussive agent to help reduce the spread of airborne infectious diseases such as tuburculosis. It was marketed in 1911. Dihydrocodeine is metabolized to dihydromorphine -- a highly active metabolite with a high affinity for mu opioid receptors. Dihydrocodeine is used for the treatment of moderate to severe pain, including post-operative and dental pain. It can also be used to treat chronic pain, breathlessness and coughing. In heroin addicts, dihydrocodeine has been used as a substitute drug, in doses up to 2500mg/day to treat addiction.

Racemorphan is racemic mixture of an antitussive and dissociative hallucinogen Dextrorphan and an opioid analgesic Levorphanol. Racemorphan itself is under international control per the Single Convention on Narcotic Drugs 1961 and is therefore listed as a Schedule II Narcotic controlled substance.

Nalorphine has a mixed opioid agonist-antagonist properties. Nalorphine inhibits the cholinesterases of mouse brain, bovine erythrocytes and horse serum. It acts on mu-, k- and sigma-opioid receptors. Nalorfin by virtue of the agonistic effect has an analgesic effect but to a much lesser extent than morphine. Initially, before the appearance of a "pure" morphine-naloxone antagonist, nalorphine was used as an antidote for severe respiratory depression and other body function disorders caused by acute poisoning in case of an overdose of morphine, promedol, fentanyl or other narcotic analgesics, or with increased sensitivity to them. At present, nalorphine is practically not used for this purpose. It was replaced by naloxone. Large doses of nalorphine can cause nausea, cramps, drowsiness, headache, mental stimulation.

Matrine is an active alkaloid, extracted from a traditional Chinese herbs of the Sophora family. Matrine has been reported for its anti-inflammatory and neuroprotective effects. It was demonstrated that the antinociceptive effects of ( )-matrine was mediated by mu- and kappa-opioid receptors. It could dose-dependently restore the balance of Th17/Treg cytokines and attenuate the cognitive impairment in Alzheimer's disease rats. Sophora flavescens and its bioactive compound, matrine alleviated caffeine-induced hyperactivity and promoted non-rapid eye movement sleep by activating ventrolateral preoptic nucleus neurons and modulating serotonergic transmission. Clinical trial results indicate, that intramuscular matrine may be an economical, efficacious, safe drug for the treatment of chronic hepatitis B. Matrine injection may be used to protect the liver function for patients with primary hepatic carcinoma after trans-artery chemo-embolization (TAE), to relieve the liver cells damage, and to improve the tolerance of TAE, so as to perform the next TAE in time.

Tetrapeptide-15 (Endomorphin-2) is an endogenous agonist at μ-opioid receptors (μORs) in the spinal cord; it exhibits antinociceptive/analgesic, immunosuppressive, and pro-angiogenic activities. Endomorphin-2 increases pain thresholds in animal models of thermal pain and inhibits the formation of antibodies in other cellular models. In HUVECs, this peptide stimulates proliferation, migration, adhesion, and tube formation.