MDMA is a well-balanced serotonin–norepinephrine–dopamine releasing agent (SNDRA).[17][4][10] (R)-MDMA and (S)-MDMA are both SNDRAs similarly.[17][4][10] However, (R)-MDMA is several-fold less potent than (S)-MDMA in vitro and is also less potent than (S)-MDMA in vivo in non-human primates.[4][10][3] In addition, whereas MDMA and (S)-MDMA are well-balanced SNDRAs, (R)-MDMA is comparatively much less potent as a dopamine releasing agent (~11-fold less potent in releasing dopamine than serotonin), and could be thought of instead more as a serotonin–norepinephrine releasing agent (SNRA) than as an SNDRA.[4][10][3][5] In non-human primates, (S)-MDMA demonstrated significant dopamine transporter (DAT) occupancy, whereas DAT occupancy with (R)-MDMA was undetectable.[3] Similarly, MDMA and (S)-MDMA were found to increase dopamine levels in the striatum in rodents and non-human primates, whereas (R)-MDMA did not increase striatal dopamine levels.[3][18] As such, (R)-MDMA may be less psychostimulant-like than MDMA or (S)-MDMA.[2][5]
In addition to its actions as an SNDRA, MDMA has weak affinity for the serotonin5-HT2A, 5-HT2B, and 5-HT2C receptors, where it acts as an agonist.[3] (R)-MDMA shows higher affinity for the serotonin 5-HT2A receptor than (S)-MDMA or MDMA.[3] In addition, (R)-MDMA is more potent as an agonist of the serotonin 5-HT2A receptor, acting as a weak partial agonist of this receptor, whereas (S)-MDMA shows very little effect.[3] Conversely however, (S)-MDMA is more potent as an agonist of the serotonin 5-HT2C receptor.[3][19] Based on these findings, it has been hypothesized that (R)-MDMA may be more psychedelic-like than (S)-MDMA.[2] However, although (R)-MDMA partially substitutes for lysergic acid diethylamide (LSD) in animal drug discrimination tests, it did not produce the head-twitch response, a behavioral proxy of psychedelic effects, at any tested dose.[20]
MDMA is a well-known serotonergic neurotoxin and this has been demonstrated both in animals and in humans.[3] There is evidence that the serotonergic neurotoxicity of MDMA may be driven primarily by (S)-MDMA rather than (R)-MDMA.[3] (R)-MDMA shows substantially lower or potentially no neurotoxicity compared to (S)-MDMA in animal studies.[3] This has been the case even when doses of (R)-MDMA were increased to account for its lower potency than (S)-MDMA.[3] However, more research is needed to confirm this in other species, such as non-human primates.[3] In contrast to (S)-MDMA, (R)-MDMA does not produce hyperthermia in rodents, and this may be involved in its reduced risk of neurotoxicity, as hyperthermia augments and is essential for the serotonergic neurotoxicity of MDMA.[3][5] The reduced potency of (R)-MDMA as a dopamine releasing agent may also be involved in its reduced neurotoxic potential, as dopamine release is likewise essential for the neurotoxicity of MDMA.[3] The hyperthermia of MDMA may in fact be mediated by dopamine release.[3][5] As (R)-MDMA is less neurotoxic than (S)-MDMA and MDMA or even non-neurotoxic, it may allow for greater clinical viability and prolonged regimens of drug-assisted psychotherapy.[3]
(R)-MDMA and (S)-MDMA have shown equivalent effects in terms of inducing prosocial behavior in monkeys.[3] However, (S)-MDMA shows higher potency, whereas (R)-MDMA shows greater maximal effects.[3] Conversely, (S)-MDMA does not increase prosocial behavior in mice, whereas both MDMA and (R)-MDMA do so.[3][5] MDMA and (S)-MDMA increase locomotor activity, a measure of psychostimulant-like effect, in rodents, whereas (R)-MDMA does not do so.[5] (R)-MDMA likewise showed fewer reinforcing effects than (S)-MDMA in non-human primates.[3] These findings further add to (R)-MDMA showing reduced psychostimulant-like and addictive effects compared to MDMA and (S)-MDMA.[3]
MDMA, MDA, and enantiomers at serotonin 5-HT2 receptors
Notes: The smaller the Kact or EC50 value, the more strongly the compound produces the effect. Refs:[21][10]
Clinical studies
The first modern clinical study of the comparative effects of MDMA, (R)-MDMA, and (S)-MDMA was published in August 2024.[1][2] It compared 125mg MDMA, 125mg (S)-MDMA, 125 and 250mg (R)-MDMA, and placebo.[1][2] (R)-MDMA increased any drug effect, good drug effect, drug liking, stimulation, drug high, alteration of vision, and alteration of sense of time ratings similarly to MDMA and (S)-MDMA.[2] However, (S)-MDMA 125mg was more potent in increasing subjective effects, including stimulation, drug high, happy, and open, among others, than (R)-MDMA 125 or 250mg or MDMA 125mg.[1][2] Ratings of bad drug effect and fear were minimal with MDMA, (R)-MDMA, and (S)-MDMA.[2] In contrast to expectations, (R)-MDMA did not produce more psychedelic-like effects than (S)-MDMA.[1][2] Besides subjective effects, (R)-MDMA increased heart rate, blood pressure, and body temperature similarly to MDMA and (S)-MDMA, though it was less potent in producing these effects.[2] Body temperature was notably increased to the same extent with (R)-MDMA 250mg as with MDMA 125mg and (S)-MDMA 125mg.[2]
The differences in effects between (R)-MDMA and (S)-MDMA may reflect the higher potency of (S)-MDMA rather than actual qualitative differences between the effects of (S)-MDMA and (R)-MDMA.[1][2] It was estimated that equivalent effects would be expected with (S)-MDMA 100mg, MDMA 125mg, and (R)-MDMA 300mg.[1][2] The findings of the study were overall regarded as not supporting the hypothesis that (R)-MDMA would produce equivalent therapeutic effects as (S)-MDMA or MDMA whilst reducing safety concerns.[1][2] However, more clinical studies were called for to assess the revised estimated equivalent doses of MDMA, (R)-MDMA, and (S)-MDMA.[1][2]
(R)-MDMA is under development separately by Empath Biosciences (EmpathBio) and MindMed.[7][9][8][22] It is being developed by Empath Biosciences for the treatment of PTSD and social phobia[7][9] and it is being developed by MindMed for the treatment of PDDs or autism.[8][22] As of 2024, the drug is in phase 1clinical trials for both PTSD, social phobia, and PDDs/autism.[7][8]
^ abcAnderson GM, Braun G, Braun U, Nichols DE, Shulgin AT (1978). "Absolute configuration and psychotomimetic activity". NIDA Research Monograph (22): 8–15. PMID101890.
^ abcdefSetola V, Hufeisen SJ, Grande-Allen KJ, Vesely I, Glennon RA, Blough B, et al. (June 2003). "3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") induces fenfluramine-like proliferative actions on human cardiac valvular interstitial cells in vitro". Molecular Pharmacology. 63 (6): 1223–1229. doi:10.1124/mol.63.6.1223. PMID12761331. S2CID839426.{{cite journal}}: CS1 maint: overridden setting (link)
^Rothman RB, Baumann MH, Dersch CM, Romero DV, Rice KC, Carroll FI, et al. (January 2001). "Amphetamine-type central nervous system stimulants release norepinephrine more potently than they release dopamine and serotonin". Synapse. 39 (1): 32–41. doi:10.1002/1098-2396(20010101)39:1<32::AID-SYN5>3.0.CO;2-3. PMID11071707. S2CID15573624.
^Nagai F, Nonaka R, Satoh Hisashi Kamimura K (March 2007). "The effects of non-medically used psychoactive drugs on monoamine neurotransmission in rat brain". European Journal of Pharmacology. 559 (2–3): 132–137. doi:10.1016/j.ejphar.2006.11.075. PMID17223101.
^ abRothman RB, Baumann MH (October 2003). "Monoamine transporters and psychostimulant drugs". European Journal of Pharmacology. 479 (1–3): 23–40. doi:10.1016/j.ejphar.2003.08.054. PMID14612135.
^Acquas E, Pisanu A, Spiga S, Plumitallo A, Zernig G, Di Chiara G (July 2007). "Differential effects of intravenous R,S-(+/-)-3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) and its S(+)- and R(-)-enantiomers on dopamine transmission and extracellular signal regulated kinase phosphorylation (pERK) in the rat nucleus accumbens shell and core". Journal of Neurochemistry. 102 (1): 121–132. doi:10.1111/j.1471-4159.2007.04451.x. PMID17564678.
^Kaur H, Karabulut S, Gauld JW, Fagot SA, Holloway KN, Shaw HE, et al. (2023). "Balancing Therapeutic Efficacy and Safety of MDMA and Novel MDXX Analogues as Novel Treatments for Autism Spectrum Disorder". Psychedelic Medicine. 1 (3): 166–185. doi:10.1089/psymed.2023.0023.
^Dunlap LE (2022). Development of Non-Hallucinogenic Psychoplastogens (Thesis). University of California, Davis. Retrieved 18 November 2024. Finally, since R-MDMA is known to partially substitute for LSD in animal models we decided to test both compounds in the head twitch response assay (HTR) (FIG 3.3C).3 The HTR is a well-validated mouse model for predicting the hallucinogenic potential of test drugs. Serotonergic psychedelics will cause a rapid back and forth head movement in mice. The potency measured in the HTR assay has been shown to correlate very well with the human potencies of psychedelics.18 Neither R-MDMA or LED produced any head twitches at all doses tested, suggesting that neither has high hallucinogenic potential.
^Nash JF, Roth BL, Brodkin JD, Nichols DE, Gudelsky GA (August 1994). "Effect of the R(-) and S(+) isomers of MDA and MDMA on phosphatidyl inositol turnover in cultured cells expressing 5-HT2A or 5-HT2C receptors". Neurosci Lett. 177 (1–2): 111–115. doi:10.1016/0304-3940(94)90057-4. PMID7824160.