"This substance works as an opioid receptor agonist and has been shown to potentially cause several unwanted side effects including hallucinations, depression, chills, and seizures," says Eyvazzadeh, adding that it's difficult to be sure exactly what you're consuming as kratom is an unregulated substance.
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Nalfurafine, an orally-administered, centrally-acting κ-opioid receptor agonist, is approved to treat the condition in Japan.
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LAAM acts as a μ-opioid receptor agonist. It also acts as a potent, noncompetitive α3β4 neuronal nicotinic acetylcholine receptor antagonist.
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Oxymorphone-3-methoxynaltrexonazine (OM-3-MNZ) is a morphinan-based opioid that acts as a selective μ-opioid receptor agonist, unlike the closely related mixed agonist-antagonist Oxymorphonenaltrexonazine.
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Eptazocine (Sedapain) is an opioid analgesic which was introduced in Japan by Morishita in 1987. It acts as a mixed κ-opioid receptor agonist and μ-opioid receptor antagonist.
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Dextropropoxyphene acts as a mu-opioid receptor agonist. It also acts as a potent, noncompetitive α3β4 neuronal nicotinic acetylcholine receptor antagonist, as well as a weak serotonin reuptake inhibitor.
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Eluxadoline is a μ- and κ-opioid receptor agonist and δ-opioid receptor antagonist that acts locally in the enteric nervous system, possibly decreasing adverse effects on the central nervous system.
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Mitragynine pseudoindoxyl is a μ opioid receptor agonist and δ opioid receptor antagonist and acts as a G protein biased agonist at μ opioid receptors and possesses a favourable side effect profile compared to conventional opioids.
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Niravoline is a chemical compound with the formula . It has diuretic and aquaretic effects and has been studied for its potential use for cerebral edema and cirrhosis. It exerts its pharmacological effect as a kappa opioid receptor agonist.
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Bremazocine is a κ-opioid receptor agonist related to pentazocine. It has potent and long-lasting analgesic and diuretic effects. It has 200 times the activity of morphine, but appears to have no addictive properties and does not depress breathing.
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Eclanamine (U-48,753) is a drug which was patented as an antidepressant, but was never marketed. It acts by inhibiting the reuptake of serotonin and norepinephrine. Eclanamine was discovered by accident as a derivative of the κ-opioid receptor agonist U-50,488.
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Buprenorphine/naloxone tablet Buprenorphine is a partial opioid receptor agonist. Unlike methadone and other full opioid receptor agonists, buprenorphine is less likely to cause respiratory depression due to its ceiling effect. Treatment with buprenorphine may be associated with reduced mortality. Buprenorphine under the tongue is often used to manage opioid dependence.
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Loperamide/simethicone is combination medication marketed under the trade name Imodium Multi-Symptom Relief (formerly Imodium A-D Advanced) used to treat diarrhea and gas simultaneously. It is manufactured by the McNeil Consumer Healthcare Division of McNeil PPC, Inc. Loperamide is a μ-opioid receptor agonist that works in the intestines.Imodium, drugs.
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U-69,593 is a drug which acts as a potent and selective κ1-opioid receptor agonist. In animal studies it has been shown to produce antinociception, anti- inflammation, anxiolysis (at low doses), respiratory depression, and diuresis, while having little effect on gastrointestinal motility. It also inhibits the peripheral, though not central secretion of oxytocin and vasopressin in rats.
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N-2′-Indolylnaltrexamine (INTA) is an opioid and derivative of β-naltrexamine. This molecule is loosely derived from the classical opioid morphine. This experimental drug candidate is under development as a κ-opioid receptor agonist for pain management with fewer adverse side effects. Preclinical study in mice showed potent analgesic effects with no tolerance or dependence.
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Salvinorin A can produce psychoactive experiences in humans with a typical duration of action being several minutes to an hour or so, depending on the method of ingestion. Salvinorin A is found with several other structurally related salvinorins. Salvinorin is a trans- neoclerodane diterpenoid. It acts as a kappa opioid receptor agonist and is the first known compound acting on this receptor that is not an alkaloid.
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Akuammicine is an alkaloid found in Vinca minor and Aspidosperma. It is a μ-opioid receptor agonist while also agonizing (but to a much lower, clinically insignificant degree) the κ and δ-opioid receptors. Agonistic activity at both human variants of the σ-sigma receptors has been indicated but is not yet proven, so have possible mechanisms of action at the NMDA receptor (antagonist) and glycine receptor.
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Doxpicomine (Doxpicodin, Doxpizodine) is a mild opioid analgesic drug. The drug acts as a mu-opioid receptor agonist. It is of fairly low potency, with a 400 mg dose of doxpicomine approximately equivalent in pain-killing effect to 8 mg morphine or 100 mg pethidine. It has been used as a lead compound to derive further analogues, although all compounds in this family are comparatively weak mu agonists.
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Fedotozine (INN; JO 1196 for the (-) tartrate salt) is an opioid drug of the arylacetamide series which acts as a peripherally specific selective κ1-opioid receptor agonist with preference for the κ1A subtype. It was under investigation for the treatment of gastrointestinal conditions like irritable bowel syndrome and functional dyspepsia and made it to phase III clinical trials, but ultimately development was discontinued and it was never marketed.
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DADLE ([D-Ala2, D-Leu5]-Enkephalin) is a synthetic opioid peptide with analgesic properties. Although it is often considered a selective delta opioid receptor agonist, it also binds to the μ1 subtype of mu opioid receptors. Treatment with DADLE results in transient depression of mean arterial blood pressure and heart rate.Online Medical Dictionary, enkephalin, leucine-2-alanine Its peptide sequence is Tyr-D-Ala-Gly-Phe-D-Leu.
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The leaves of the Kratom plant (Mitragyna speciosa) contain a variety of alkaloids, including several psychoactive alkaloids and is traditionally prepared and consumed in Southeast Asia, where it has been known to exhibit both painkilling and stimulant qualities, behaving as a μ-opioid receptor agonist, and often being used in traditional Thai medicine in a similar way to and often as a replacement for opioid painkillers like morphine.
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Propiram (Algeril, Dirame, Bay 4503) is a partial mu opioid receptor agonist and weak mu antagonist analgesic from the ampromide family of drugs related to other drugs such as phenampromide and diampromide. It was invented in 1963 in the United Kingdom by Bayer but was not widely marketed, although it saw some limited clinical use, especially in dentistry. Propiram reached Phase III clinical trials in the United States and Canada.
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Buprenorphine binds strongly to opioid receptors and acts as a pain-reducing medication in the central nervous system (CNS). It binds to the μ-opioid receptor with high affinity which produces the analgesic effects in the CNS. It is a partial μ-opioid receptor agonist and it is a weak κ-opioid receptor antagonist. As the dose of buprenorphine increases, its analgesic effects reach a plateau, and then it starts to act like an antagonist.
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The most potent narcotic component of opium is the alkaloid morphine which acts as an opioid receptor agonist. A more recent example is the N-type calcium channel blocker ziconotide analgesic which is based on a cyclic peptide cone snail toxin (ω-conotoxin MVIIA) from the species Conus magus. A significant number of anti-infectives are based on natural products. The first antibiotic to be discovered, penicillin, was isolated from the mold Penicillium.
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Meptazinol (trade name Meptid) is an opioid analgesic developed by Wyeth in the 1970s. Indications for use in moderate to severe pain, most commonly used to treat pain in obstetrics (childbirth). Meptazinol is a 3-phenylazepane derivative, whereas the other phenazepanes like ethoheptazine and proheptazine are 4-phenylazepanes. A partial μ-opioid receptor agonist, its mixed agonist/antagonist activity affords it a lower risk of dependence and abuse than full μ agonists like morphine.
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Levomethadone (the L enantiomer) is a μ-opioid receptor agonist with higher intrinsic activity than morphine, but lower affinity. Dextromethadone (the S enantiomer) does not affect opioid receptors but binds to the glutamatergic NMDA (N-methyl--aspartate) receptor, and acts as an antagonist against glutamate. Methadone has been shown to reduce neuropathic pain in rat models, primarily through NMDA receptor antagonism. Glutamate is the primary excitatory neurotransmitter in the central nervous system.
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Active and inactive μ-opioid receptors The μ-opioid receptors (MOR) are a class of opioid receptors with a high affinity for enkephalins and beta- endorphin, but a low affinity for dynorphins. They are also referred to as μ(mu)-opioid peptide (MOP) receptors. The prototypical μ-opioid receptor agonist is morphine, the primary psychoactive alkaloid in opium. It is an inhibitory G-protein coupled receptor that activates the Gi alpha subunit, inhibiting adenylate cyclase activity, lowering cAMP levels.
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4-Fluoroisobutyrylfentanyl (also known as 4-FIBF and p-FIBF) is an opioid analgesic that is an analog of butyrfentanyl and structural isomer of 4-Fluorobutyrfentanyl and has been sold online as a designer drug. It is closely related to 4-fluorofentanyl, which has an EC50 value of 4.2 nM for the human μ-opioid receptor. 4-fluoroisobutyrylfentanyl is a highly selective μ-opioid receptor agonist whose analgesic potency is almost ten times of that reported for morphine.
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Morphiceptin is a tetrapeptide (Tyr-Pro-Phe-Pro-NH2) that is a selective μ-opioid receptor agonist. It is derived from β-casomorphin and has over 1,000 times selectivity for μ- over δ-opioid receptors. When injected intracerebroventricularly (into the ventricular system of the brain), morphiceptin had an analgesic ED50 of 1.7 nmol per animal. The analgesic effects of morphiceptin were reversed by naloxone, meaning that the analgesic effect is mediated by the μ-opioid receptor.
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In 1997, a group of Australian researchers proposed (based on a study in rats) that oxycodone acts on KORs, unlike morphine, which acts upon MORs. Further research by this group indicated the drug appears to be a high-affinity κ2b-opioid receptor agonist. However, this conclusion has been disputed, primarily on the basis that oxycodone produces effects that are typical of MOR agonists. In 2006, research by a Japanese group suggested the effect of oxycodone is mediated by different receptors in different situations.
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C-8813 (thiobromadol) is a potent μ-opioid receptor agonist with a distinctive chemical structure which is not closely related to other established families of opioid drugs. The trans-isomer was found to be around 591 times more potent than morphine in animal studies. The same study assigned a potency of 504 times that of morphine to the related compound BDPC. C-8813 is claimed to be similarly potent at the δ-opioid receptor, which antagonizes the mu depression of breathing, presumably making the drug safer.
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Morphine, the archetypal opioid, and other opioids (e.g., codeine, oxycodone, hydrocodone, dihydromorphine, pethidine) all exert a similar influence on the cerebral opioid receptor system. Buprenorphine is a partial agonist of the μ-opioid receptor, and tramadol is a serotonin norepinephrine reuptake inhibitor (SNRI) with weak μ-opioid receptor agonist properties. Tramadol is structurally closer to venlafaxine than to codeine and delivers analgesia by not only delivering "opioid-like" effects (through mild agonism of the mu receptor) but also by acting as a weak but fast-acting serotonin releasing agent and norepinephrine reuptake inhibitor.
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Methadone maintenance treatment (MMT), a form of opioid replacement therapy, reduces and/or eliminates the use of illegal opiates, the criminality associated with opiate use, and allows patients to improve their health and social productivity. Methadone is a μ-opioid receptor agonist. If initial doses during the beginning of treatment are too high or are concurrent with illicit opioid use, this may present an increased risk of death from overdose. In addition, enrollment in methadone maintenance has the potential to reduce the transmission of infectious diseases associated with opiate injection, such as hepatitis and HIV.
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However, in 2013, Canadian police seized 3 kilograms of acetylfentanyl. As a μ-opioid receptor agonist, acetylfentanyl may serve as a direct substitute for heroin or other opioids. Common side effects of fentanyl analogs are similar to those of fentanyl itself, which include itching, nausea and potentially serious respiratory depression, which can be life-threatening. Fentanyl analogs have killed hundreds of people throughout Europe and the former Soviet republics since the most recent resurgence in use began in Estonia in the early 2000s, and novel derivatives continue to appear.
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Frakefamide (INN) is a synthetic, fluorinated linear tetrapeptide with the amino acid sequence Tyr-D-Ala-(p-F)Phe-Phe-NH2 which acts as a peripherally- specific, selective μ-opioid receptor agonist. Despite its inability to penetrate the blood-brain-barrier and enter the central nervous system, frakefamide has potent analgesic effects and, unlike centrally-acting opioids like morphine, does not produce respiratory depression, indicating that its antinociceptive effects are mediated by peripheral μ-opioid receptors. It was under development for the treatment of pain by AstraZeneca and Shire but was shelved after phase II clinical trials.
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The European Food Safety Authority (EFSA) reviewed the scientific literature and published their results in 2009. As part of their evaluation, the EFSA looked at the laboratory studies that had been done on BCM-7 that found that BCM-7 can act as a weak opioid receptor agonist. The EFSA found no relationship between any disease and drinking milk with the A1 protein. In most of the animal studies, BCM-7 was not administered orally, as humans would be exposed to it, but rather was given to animals by injection into the peritoneal cavity or directly into the spinal cord or brain.
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Oligomers; specifically 5-HT2A– heteromers mediate this effect. This may explain why some direct 5-HT2 receptor agonists have psychedelic effects, whereas compounds that indirectly increase serotonin signaling at the 5-HT2 receptors generally do not, for example: selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), and medications using 5HT2A receptor agonists that do not have constitutive activity at the mGluR2 dimer, such as lisuride. Tianeptine, an atypical antidepressant, is thought to exhibit functional selectivity at the μ-opioid receptor to mediate its antidepressant effects. Oliceridine is a mu opioid receptor agonist that has been described to be functionally selective towards G protein and away from β-arrestin2 pathways .
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Adrenorphin, also sometimes referred to as metorphamide, is an endogenous, C-terminally amidated, opioid octapeptide (Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val- NH2) that is produced from proteolytic cleavage of proenkephalin A and is widely distributed throughout the mammalian brain. It was named based on the fact that it was originally detected in human phaeochromocytoma tumour derived from the adrenal medulla, and was subsequently found in normal human and bovine adrenal medulla as well. Adrenorphin exhibits potent opioid activity, acting as a balanced μ- and κ-opioid receptor agonist while having no effects on δ-opioid receptors. It possesses analgesic and respiratory depressive properties.
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PZM21 is an experimental opioid analgesic drug that is being researched for the treatment of pain. It is claimed to be a functionally selective μ-opioid receptor agonist which produces μ-opioid receptor mediated G protein signaling, with potency and efficacy similar to morphine, but with less β-arrestin 2 recruitment . However, recent reports highlight that this might be due to its low intrinsic efficacy , rather than functional selectivity or 'G protein bias' as initially reported. In tests on mice, PZM21 was slightly less potent than morphine or TRV130 as an analgesic, but also had significantly reduced adverse effects, with less constipation than morphine, and very little respiratory depression, even at high doses.
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IBNtxA, or 3-iodobenzoyl naltrexamine, is an atypical opioid analgesic drug derived from naltrexone. In animal studies it produces potent analgesic effects that are blocked by levallorphan and so appear to be μ-opioid mediated, but it fails to produce constipation or respiratory depression, and is neither rewarding or aversive in conditioned place preference protocols. These unusual properties are thought to result from agonist action at a splice variant or heterodimer of the μ-opioid receptor, rather than at the classical full length form targeted by conventional opioid drugs.Keck TM, Uddin MM, Babenko E, Wu C, Moura-Letts G. Abuse Liability and Anti-Addiction Potential of the Atypical Mu Opioid Receptor Agonist IBNtxA.
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The drug combination morphine/naltrexone (trade name Embeda) is an opioid combination pain medication developed by King Pharmaceuticals for use in moderate to severe pain. The active ingredients are morphine sulfate and naltrexone hydrochloride; morphine being an opioid receptor agonist and naltrexone an opioid receptor antagonist. It is a schedule 2 controlled substance, and is intended for long-term pain caused by malignancy or where lower tiers of the pain management ladder have already been exhausted, and where medications such as oxycodone would otherwise have been indicated. King Pharmaceuticals temporarily recalled Embeda in 2011 after complaints from the FDA in regard to King Pharmaceuticals omitting information regarding the potentially fatal reaction if crushed and swallowed and also for making unsubstantiated claims regarding Embeda's reduced abuse potential.
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Leumorphin, also known as dynorphin B1–29, is a naturally occurring endogenous opioid peptide. Derived as a proteolytic cleavage product of residues 226-254 of prodynorphin (preproenkephalin B), leumorphin is a nonacosapeptide (29 amino acids in length) and has the sequence Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Gln- Phe-Lys-Val-Val-Thr-Arg-Ser-Gln-Glu-Asp-Pro-Asn-Ala-Tyr-Ser-Gly-Glu-Leu-Phe- Asp-Ala. It can be further reduced to dynorphin B (dynorphin B-13) and dynorphin B-14 by pitrilysin metallopeptidase 1 (formerly referred to as "dynorphin-converting enzyme"), an enzyme of the endopeptidase family. Leumorphin behaves as a potent and selective κ-opioid receptor agonist, similarly to other endogenous opioid peptide derivatives of prodynorphin.
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