Ephenidine

Ephenidine, also known as N-ethyl-1,2-diphenylethylamine or NEDPA, is a synthetic dissociative in the diarylethylamine family. It was developed in early research on local anaesthetics and later appeared on the new psychoactive substance market as a ketamine-like compound. Laboratory studies show that it blocks NMDA receptors, while evidence about its effects and toxicity in people remains limited.

Chemistry and history

Ephenidine has two phenyl rings attached to an ethylamine chain, with an ethyl group on the nitrogen. It is related to diphenidine and methoxphenidine, but differs in the substituents attached to the aromatic rings. Unlike ketamine and PCP, it does not contain a cyclohexyl ring, so it belongs to the diarylethylamines rather than the arylcyclohexylamines.

The compound was described in the context of research chemicals that emerged after controls were introduced for other dissociatives. It became available online in the mid-2010s and was marketed as an alternative to ketamine-like substances.

Pharmacology

Ephenidine is an NMDA receptor antagonist. In receptor-binding experiments it displaced MK-801 from the PCP site of the NMDA receptor, with a reported affinity of 66 nM. The same study found weaker interactions with the dopamine and norepinephrine transporters and with sigma receptors. Electrophysiological experiments showed voltage-dependent blockade of NMDA-mediated responses in rat hippocampal neurons, similar in broad outline to ketamine (Ephenidine: a new psychoactive agent with ketamine-like NMDA receptor antagonist properties, 2017).

At higher experimental concentrations, ephenidine inhibited long-term potentiation in hippocampal slices. This is consistent with NMDA receptor blockade, but does not by itself explain the full range of subjective effects.

Subjective effects

The PsychonautWiki profile of ephenidine lists sedation, altered perception and detachment from the body among the reported dissociative effects. These accounts are anecdotal, with no controlled human studies to establish a typical experience.

Physical effects

Reports include sedation, dizziness, analgesia and impaired coordination. Some users describe bodily lightness or a sense of physical detachment, while stronger effects may make movement and balance difficult. Nausea and changes in tactile perception are also mentioned.

Cognitive and perceptual effects

Reported effects include changes in time perception, memory disruption, confusion and dream-like thinking. Dissociation may involve a sense of separation from the surroundings or the body. More intense accounts mention hallucinations and out-of-body experiences, although the frequency of these effects is unknown.

Clinical evidence and toxicity

The UK Advisory Council on the Misuse of Drugs reported in 2023 that no published acute-poisoning case reports or case series had been attributed to ephenidine. The same review summarised its NMDA receptor activity and noted that its prevalence of use is unknown (ACMD review of diphenidine and related substances, 2023).

The absence of published cases does not establish that ephenidine is safe. Its toxic range, metabolism, dependence potential and long-term effects have not been adequately studied. Reports of dependence and withdrawal involving related diarylethylamines should not automatically be attributed to ephenidine.

Related compounds

Ephenidine is related to Diphenidine and MXP (methoxphenidine). All three are diarylethylamines with NMDA receptor antagonist activity, but their receptor affinities and reported effects differ.