Arbaclofen (STX209, R-baclofen), a selective agonist of GABA-B receptors, has been investigated in clinical trials for the treatment of autism spectrum disorder ASD, phase II and for the treatment of patients with fragile X syndrome in phase III. As a result, the drug did not meet the primary outcome of improved social avoidance in FXS in either study. In spite of positive results in some children with ASD, further study will be needed to replicate and extend these initial findings. Arbaclofen has also been investigated in phase III clinical trials as a treatment for spasticity due to multiple sclerosis.

Dioxaphetyl butyrate is a synthetic narcotic analgesic and spasmolytic agent that has no accepted medicinal value in the United States. This opioid drug under international control according to the UN Single Convention 1961 and its amendments, Schedule I.

Xenbucin is an antihyperlipidemic agent. Information about the current use of this agent is not available.

Ticalopride is an isomer of the active metabolite of cisapride, which is marketed by Janssen for the treatment of nocturnal heartburn due to gastroesophageal reflux disease. Ticalopride acts through the stimulation of the serotonin 5-HT4 receptors which increases acetylcholine release in the enteric nervous system (specifically the myenteric plexus). This results in increased tone and amplitude of gastric contractions, relaxation of the pyloric sphincter and the duodenal bulb, and increased peristalsis of the duodenum and jejunum resulting in accelerated gastric emptying and intestinal transit. Phase II clinical trials of the Ticalopride are being suspended while investigators study reports of adverse events in patients with gastroesophageal reflux disease and diabetes.

Brifentanii, a potent narcotic analgesic structurally similar to alfentanil, that was studied in clinical trials in the early 1990s. The effects of brifentanil are very similar to those of alfentanil, with strong but short lasting analgesia and sedation, and particularly notable itching and respiratory depression. Side effects of Brifentanii are similar to those of fentanyl itself, which include itching, nausea and potentially serious respiratory depression, which can be life-threatening.

Tifurac is a benzofuranacetic acid derivative patented by Syntex, Inc. as an analgesic, anti-inflammatory, and antipyretic agent. In preclinical models, Tifurac can exert anti-inflammatory and analgesic activity in rat paw edema assay and mouse writhing assay.

The selective kappa-opioid receptor agonist spiradoline (U62,066E), an arylacetamide, was synthesized with the intention of creating an analgesic that, while still retaining its analgesic properties, would be devoid of the, mainly mu receptor mediated, side effects such as physical dependence and respiratory depression associated with morphine. The racemate spiradoline was found to be highly selective for the kappa receptor, with a Ki of 8.6 nM in the guinea pig. Examination of the enantiomers of spiradoline, showed the (-)enantiomer to be responsible for the kappa agonist properties. Spiradoline easily penetrates the blood brain barrier, and does not seem to have any significant active metabolites. In preclinical studies, spiradoline has a short duration of action with a peak at around 30 min after administration. The analgesic properties of spiradoline are well documented in mice and rats. Antitussive properties have also been reported in rats. Spiradoline was reported to display effects suggestive of neuroprotective properties in animal models of ischemia. In humans, spiradoline is a potent diuretic. It also produces significant sedation presumably due to its antihistamine properties. Preclinical studies have shown that spiradoline reduces blood pressure and heart rate, and has possible antiarrhythmic properties. Clinical studies did not confirm these findings. Although spiradoline had promising effects in animal tests of analgesia, and a reasonably good safety profile in preliminary studies, it did not replace morphine as an analgesic. The available clinical data suggest that spiradoline produces disturbing adverse effects such as diuresis, sedation, and dysphoria at doses lower than those needed for analgesic effects. Spiradoline was in phase II clinical trials with Pharmacia & Upjohn in Japan and the USA, principally for the treatment of pain. However, the commercial development of spiradoline has been discontinued.

Racemethorphan is racemic mixture of Dextromethorphan and Levomethorphan. Racemethorphan is listed under the Single Convention on Narcotic Drugs 1961 and is therefore listed in the United States as a Controlled Substance, specifically as a Narcotic in Schedule II. Dextromethorphan is a non-narcotic morphine derivative widely used as an antitussive. Dextromethorphan is a cough suppressant in many over-the-counter cold and cough medicines. In 2010, the FDA approved the combination product dextromethorphan/quinidine for the treatment of pseudobulbar affect. Dextromethorphan suppresses the cough reflex by a direct action on the cough center in the medulla of the brain. Levomethorphan is an opioid analgesic of the morphinan family that has never been marketed.

Tazadolene was developed as a novel non-opioid analgesic with antidepressant properties. Experiments on rodents have revealed that unique analgesia properties of tazadolene was due to the ability of this compound to activate both serotonergic and alpha 2 adrenergic antinociceptive systems. Information about the current use of this drug is not available.