Significance of mammalian N, N-dimethyltryptamine (DMT): A 60-year-old debate

This is a narrative review integrating historical and contemporary literature on endogenous DMT rather than an empirical study with a defined protocol. The author reviewed evidence on CNS DMT concentrations from cerebrospinal fluid and brain tissue measurements; the expression, localisation, and kinetics of biosynthetic enzymes (aromatic L-amino acid decarboxylase, AADC; indolethylamine N-methyltransferase, INMT) and catabolic enzymes (monoamine oxidase, MAO) in neural tissue; the capacity for vesicular storage via the vesicular monoamine transporter 2 (vMAT2) and serotonin transporter (SERT); receptor binding and functional data across serotonin receptors, TAARs, and sigma-1; and single-neuron electrophysiological recordings documenting the effects of local DMT application on neuronal firing in cat and rat brain.

Endogenous DMT has been detected in human cerebrospinal fluid and in rat brain tissue. Critically, available evidence suggests that DMT can be present at CNS concentrations approaching approximately half those of serotonin — a level substantially higher than is consistent with the classification of DMT as a conventional trace amine. Both biosynthetic enzymes (AADC for tryptophan decarboxylation to tryptamine, and INMT for N-methylation to DMT) are expressed in neural tissue, though the distribution and kinetics of INMT remain incompletely characterised and debated. DMT is taken up into presynaptic terminals via SERT and can be concentrated in synaptic vesicle-associated fractions presumably through vMAT2 — a property that distinguishes it from classical trace amines. DMT is pharmacologically promiscuous, acting as an agonist at 5-HT1A, 5-HT2A, 5-HT2B, 5-HT2C, rodent TAAR1, and sigma-1 receptors, as well as showing binding at dopamine D1, adrenergic, and imidazoline receptors. Electrophysiological recordings demonstrated predominantly inhibitory effects of local DMT application in the brainstem (consistent with high 5-HT1A expression), but facilitatory effects in hippocampal CA1 and septal nuclei.

The review argues that the weight of available evidence is no longer consistent with treating endogenous DMT as a pharmacologically inert trace amine. Its CNS concentrations, its capacity for vesicular storage, its biosynthetic enzyme expression in neural tissue, and its potent activity at multiple receptors collectively support the hypothesis that DMT serves a physiologically relevant endogenous function — though the nature of that function remains to be determined. The sigma-1 receptor is identified as a particularly intriguing target given sigma-1's role in neuroplasticity, neuroprotection, and modulation of ion channels, and its potential to mediate effects at concentrations lower than those required for psychedelic action via 5-HT2A. The author draws an analogy to the opioid receptor system: understanding endogenous DMT will improve understanding of psychedelic drugs, just as understanding endogenous opioids improved the therapeutic use of opiates. Sixty years of intermittent research have left the fundamental question of endogenous DMT's physiological role unresolved, in part because current research priorities favour DMT as a clinical drug over DMT as an endogenous molecule.

After 60 years of debate, the physiological significance of endogenous mammalian DMT remains unresolved, yet the accumulated evidence indicates that its CNS presence is robust and very likely active. DMT is produced and degraded by enzymes expressed in neural tissue, can be concentrated in synaptic vesicle fractions, and acts at multiple pharmacologically relevant receptors including 5-HT2A, TAAR1, and sigma-1. Its concentrations appear substantially higher than those of classical trace amines. A focused research programme — directed at characterising INMT expression and activity in human brain, elucidating the conditions that regulate DMT synthesis and release, and identifying the behavioural and physiological consequences of endogenous DMT signalling — is overdue and would substantially advance understanding of both endogenous indolamine neurotransmission and the mechanisms through which exogenous DMT exerts its psychedelic effects.