Tapentadol is the first US FDA-approved centrally acting analgesic having both μ-opioid receptor agonist and noradrenaline (norepinephrine) reuptake inhibition activity with minimal serotonin reuptake inhibition. Tapentadol is indicated for the management of pain severe enough to require daily, around-the-clock, long-term opioid treatment and for which alternative treatment options are inadequate, neuropathic pain associated with diabetic peripheral neuropathy (DPN) severe enough to require daily, around-the-clock, long-term opioid treatment and for which alternative treatment options are inadequate.

Butorphanol is a synthetic opioid agonist-antagonist analgesic with a pharmacological and therapeutic profile that has been well established since its launch as a parenteral formulation in 1978. The introduction of a transnasal formulation of butorphanol represents a new and noninvasive presentation of an analgesic for moderate to severe pain. This route of administration bypasses the gastrointestinal tract, and this is an advantage for a drug such as butorphanol that undergoes significant first-pass metabolism after oral administration. The onset of action and systemic bioavailability of butorphanol following transnasal delivery are similar to those after parenteral administration. Butorphanol blocks pain impulses at specific sites in the brain and spinal cord. Butorphanol has agonistic activity at the κ-receptor and antagonistic activity at the μ-receptor. It also exhibits partial agonistic activity at the σ-receptor.

Hydromorphone (also known as dihydromorphinone and the brand name Dilaudid among others) is a more potent opioid analgesic than morphine and is used for moderate to severe pain. It can be administered by injection, by infusion, by mouth, and rectally. Oral bioavailability is low. The kidney excretes hydromorphone and its metabolites. Some metabolites may have greater analgesic activity than hydromorphone itself but are unlikely to contribute to the pharmacological activity of hydromorphone. With the exception of pruritus, sedation and nausea and vomiting, which may occur less after hydromorphone than after morphine, the side-effects of these drugs are similar. Hydromorphone interacts predominantly with the opioid mu-receptors. These mu-binding sites are discretely distributed in the human brain, with high densities in the posterior amygdala, hypothalamus, thalamus, nucleus caudatus, putamen, and certain cortical areas. It also binds with kappa and delta receptors which are thought to mediate spinal analgesia, miosis and sedation.

Pentazocine is a synthetically prepared prototypical mixed agonist-antagonist narcotic (opioid analgesic) drug of the benzomorphan class of opioids used to treat moderate to moderately severe pain. Pentazocine is sold under several brand names, such as Fortral, Sosegon, Talwin NX. Pentazocine acts as an agonist of κ-opioid receptors and as an antagonist of μ-opioid receptors. This compound may exist as one of two enantiomers, named (+)-pentazocine and (−)-pentazocine. Side effects are similar to those of morphine, but pentazocine, due to its action at the kappa opioid receptor is more likely to invoke psychotomimetic effects. High dose may cause high blood pressure or high heart rate.

Levorphanol, brand name Levo-Dromoran, is an opioid medication used to treat moderate to severe pain. Levorphanol is indicated for the management of moderate to severe pain where an opioid analgesic is appropriate. It is a potent synthetic opioid mu-receptor agonist similar in action to morphine. Like other opioid mu-receptor agonists, it is believed to act at receptors in both the brain and spinal cord to alter the transmission and perception of pain. The onset and peak analgesic effects following administration of levorphanol are similar to morphine when administered at equal analgesic doses. Levorphanol produces a degree of respiratory depression similar to that produced by morphine at equal analgesic doses, and like many opioid mu-receptor agonists, levorphanol produces euphoria or has a positive effect on mood in many individuals.

Pethidine, also known as meperidine and Demerol, a narcotic analgesic that can be used for the relief of most types of moderate to severe pain, including postoperative pain and the pain of labor. Meperidine is an opioid agonist with multiple actions qualitatively similar to those of morphine. Most common adverse reactions were lightheadedness, dizziness, sedation, nausea, vomiting, and sweating. Pethidine has serious interactions that can be dangerous with monoamine oxidase inhibitors (e.g., furazolidone, isocarboxazid, moclobemide, phenelzine, procarbazine, selegiline, tranylcypromine). Pethidine can interact with muscle relaxants, some antidepressants, benzodiazepines, and ethanol.

Faxeladol (GRT9906) is a μ-opioid receptor agonist and inhibitor of noradrenalin/serotonin re-uptake. Faxeladol was being studied in the treatment of fibromyalgia and neuropathic pain, however its development has been discontinued.

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.

Saccharin is the most established of the artificial sweeteners on the market, this mixture of dextrose and saccharin has been in use for over a century and is found in diet versions of soft drinks. It is 300-500 times sweeter than sugar and contains zero calories. In 1977, the FDA tried to ban its use after evidence showed it caused cancer in rats. Extensive lobbying by the diet food industry allowed products to stay on the shelves as long as they carried warnings about the cancer risks in animals. This warning was removed in 2001 when the Calorie Control Council insisted the link between animal and human cancers could not automatically be made. Consumption of saccharin-sweetened products can benefit diabetics as the substance goes directly through the human digestive system without being digested. While saccharin has no food energy, it can trigger the release of insulin in humans due to its sweet taste. The T1R2/R3 sweet taste receptor exist on the surface of pancreatic beta cells. Saccharin is a unique in that it inhibits glucose-stimulated insulin secretion (GSIS) at submaximal and maximal glucose concentrations, with the other sweeteners having no effect. Investigation of saccharin’s dose-response characteristics showed that concentrations of 0.1 and 0.5 mM stimulated insulin secretion, while concentrations of 1 and 2.5 mM inhibited insulin secretion. Saccharin’s effect on insulin secretion was shown to be reversible in INS-1 832/13 clonal pancreatic beta cells after chronic exposure to 1 mM saccharin. Artificial sweeteners may affect insulin secretion via interaction with the sweet taste receptor, also saccharin may affect other cellular processes linked to insulin secretion, and that these effects are both time- and concentration-dependent

Levomethadyl acetate (LAAM) is a synthetic opioid agonist with actions qualitatively similar to morphine (a prototypic mu agonist) and affecting the central nervous system (CNS) and smooth muscle. Principal actions include analgesia and sedation. Tolerance to these effects develops with repeated use. An abstinence syndrome generally occurs upon cessation of chronic administration similar to that observed with other opiates, but with slower onset, more prolonged course, and less severe symptoms. LAAM exerts its clinical effects in the treatment of opiate abuse through two mechanisms. First, LAAM cross-substitutes for opiates of the morphinetype, suppressing symptoms of withdrawal in opiate-dependent individuals. Second, chronic oral administration of LAAM can produce sufficient tolerance to block the subjective “high” of usual doses of parenterally administered opiates. Since the introduction of levomethadyl in 1995, the manufacturer has received increasing reports of severe cardiac-related adverse events, including QT interval prolongation, Torsades de Pointes and cardiac arrest. Other cardiac-related adverse events have also been reported, including arrhythmias, syncope, and angina. These events led to the removal of levomethadyl from the European market in March 2001. A very small number of patients may benefit from levomethadyl, but the risk of continued distribution and use no longer outweighs the overall benefits.