The 2019 DMT rat brain study, explained: what it measured and what it didn’t

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If you have read that “scientists found DMT in the brain” or that “the brain makes DMT as you die”, the study behind it is almost certainly this one: Dean and colleagues, published in Scientific Reports on 27 June 2019 (Dean et al., 2019). It is a careful, interesting piece of work. It is also a rat study, from one laboratory, with limits its own authors spelled out.

This explainer goes through what the team did, the actual numbers, what the coverage said, and what later studies changed. For the wider human picture, see does the brain make DMT?.

What question was the study trying to answer?

By 2019, DMT had been reported in rats and in human body fluids, but whether it is made in the mammalian brain was, in the authors’ words, unknown. The enzyme credited with making it, INMT, had been found at high levels in body tissues such as lung, but at very low levels in rabbit brain and not at all in human brain in earlier surveys, and no study had found it in the cerebral cortex of any species. Their own lab had detected DMT in 2013 near the rat pineal gland, but had not measured how much, and could not say whether it came from the pineal or the surrounding cortex (Dean et al., 2019; Barker et al., 2013). Evidence: established as the state of knowledge the paper describes.

What did the researchers actually do?

1. Stained thin slices of rat brain and archived human autopsy brain tissue with RNAscope, a sensitive in situ hybridisation method, to look for INMT messenger RNA.
2. Ran double staining on rat tissue to see whether INMT and AADC (the enzyme that turns tryptophan into tryptamine) messages sat in the same cells, in the brain and in the adrenal gland, kidney, lung and heart.
3. Implanted microdialysis probes in 36 adult male Wistar rats: 25 with the pineal gland intact and 11 whose pineal gland had first been surgically removed. The rats recovered for a week (Dean et al., 2019).
4. Sampled fluid from the visual cortex of freely moving rats every 15 or 30 minutes for hours or days, analysed online by liquid chromatography with fluorescence detection (Dean et al., 2019).
5. Euthanised the rats with an injection to the heart, and compared DMT before and after what the paper calls experimentally induced cardiac arrest (Dean et al., 2019).
6. For the 11 rats without a pineal gland, also measured serotonin in the same samples for comparison (Dean et al., 2019).

Each step is from the methods section (Dean et al., 2019). Two details matter later. First, DMT was identified by its retention time against reference standards and its natural fluorescence, not by mass spectrometry. Second, the rats were not given anything to block monoamine oxidase, the enzyme that rapidly breaks DMT down, so what was measured is DMT that survived normal breakdown. Evidence: established for the design.

How much DMT was in the rat brain?

Concentrations below are in nanomolar (nM), billionths of a mole per litre of fluid, the usual unit for brain chemicals sampled this way. Rats with a pineal gland averaged 0.56 nM and rats without one 1.02 nM (Dean et al., 2019); these are the figures our other DMT articles use.

• The baseline difference between the two groups was not statistically significant (p = 0.05 on the test used), and neither was the difference after cardiac arrest (Dean et al., 2019).
• In the 11 rats without a pineal gland, average serotonin in the same samples was 2.10 nM, so DMT was about half the serotonin level (Dean et al., 2019).
• The authors compared their DMT figures with published microdialysis averages for serotonin (0.87 nM), noradrenaline (1.77 nM) and dopamine (1.5 nM) in rat brain, and concluded DMT is in the same range (Dean et al., 2019).
• INMT messenger RNA was found in rat visual cortex, human medial frontal cortex, and the pineal gland and choroid plexus of both species. In rat brain it overlapped extensively with AADC messages, including in the hippocampus; in rat lung, heart, kidney and adrenal gland the two rarely overlapped.

All figures are from the paper’s results, figure legends and discussion (Dean et al., 2019). One small wrinkle for careful readers: in one passage the discussion attributes the 1.02 nM average to the pineal-intact panel, while the results and figure legend give 0.56 nM for those rats and 1.02 nM for rats without a pineal gland. We use the figure-legend values. Evidence: preliminary. Measured in rats, by one lab.

What exactly did the cardiac-arrest result show?

This is the finding that travelled furthest, so it is worth stating precisely. After the researchers stopped the rats’ hearts, DMT in visual-cortex fluid rose significantly in both groups, within about an hour. In rats with a pineal gland, 15 of 25 (60%) showed more than a two-fold rise, while 8 of 25 (32%) changed by less than 1.5-fold. In rats without one, 5 of 11 showed more than a two-fold rise and 6 of 11 showed minimal change. The average rise was 2.84-fold with the pineal and 1.84-fold without (Dean et al., 2019). Evidence: preliminary. One rat study.

The authors linked this, cautiously, to near-death experiences. They pointed to a human study in which DMT given in the lab produced experiences resembling near-death experiences (Timmermann et al., 2018), and noted that not every rat showed a surge, just as fewer than 20% of people who survive cardiac arrest report a near-death experience. Then they set out the limits themselves (Dean et al., 2019):

• It is unknown whether the DMT concentrations seen at cardiac arrest can produce the effects of a psychedelic dose of DMT.
• It is unknown whether a similar surge happens in humans.
• Several other neurotransmitters also surge at cardiac arrest in rats, and these may contribute to near-death states.

What are the study’s main limits?

• Species and sample: 36 male rats of one strain. No females, no other species, and no human brain measurement (Dean et al., 2019).
• Method of identification: DMT was identified by fluorescence and retention time, not mass spectrometry. In a 2023 paper the same lab describes the 2019 work this way, and contrasts it with its 2013 study, which used mass spectrometry to confirm DMT (Glynos et al., 2023). A 2018 review treats mass-spectrometry evidence as the standard that separated reliable reports of human DMT from earlier misidentifications (Barker, 2018).
• One laboratory: the 2013 detection, the 2019 measurements and the 2023 knockout study all come from the same Michigan group, and authors of the 2019 paper include Steven Barker and Rick Strassman, long associated with the endogenous-DMT hypothesis (Dean et al., 2019).
• Messenger RNA is not enzyme activity: the human evidence is INMT messenger RNA in autopsy tissue, not DMT, and not proof the enzyme was active (Dean et al., 2019).
• The authors themselves said INMT-deficient animals would be needed to show INMT makes the DMT (Dean et al., 2019). When that was done, the result raised new questions (next section).

None of this means the study is wrong. Its authors reported p-values, confidence intervals and their own uncertainties, and they declared no competing interests (Dean et al., 2019). It means the result is a strong first measurement in rats that still needs independent confirmation. Evidence: preliminary.

How did the headlines describe it?

The University of Michigan’s own news release was headlined “‘Mystical’ psychedelic compound found in normal brains”, without saying rat in the headline. The body was more careful: it described rat experiments, quoted the lab’s leader, Jimo Borjigin, saying “We don’t know what it’s doing in the brain”, and noted that whether the human brain makes DMT the same way remained open (University of Michigan release). The lab’s own news page summarises the work as finding DMT “in lab rat brains” under a headline about “mammal brains” (Borjigin lab). Evidence: established for what the coverage said.

Inverse, a science news site, headlined its story “A Natural Source of DMT Has Been Discovered in Mammal Brains”, described the paper as primarily a rat study, and reported that Borjigin told the outlet the evidence was “very strong in rats and humans”, while adding that the idea of human levels reaching that point is still contested (Inverse, 2019). The gap is worth noticing: the paper measured DMT in rat brains and found only enzyme messages in human tissue, and its own conclusion was that the results “raise the possibility” that this happens in human brains (Dean et al., 2019). Evidence: established for the wording; the human claim is unresolved.

What did later studies change?

In 2023, the same lab made rats with the INMT gene knocked out. Brain and lung tissue from those rats still methylated tryptamine at the same level as normal tissue, but the products were neither N-methyltryptamine nor DMT, and rat INMT made in the lab could not methylate tryptamine at all, unlike rabbit and human INMT. The authors concluded that an alternative pathway likely makes DMT in rats (Glynos et al., 2023). In 2025, a different team reported that INMT-knockout mice showed no obvious decrease in endogenous psychedelic levels (Hatzipantelis et al., 2025). Evidence: preliminary. The 2019 enzyme maps still stand as maps; what they mean for DMT production is now less clear.

The interpretation debate also continued. Steven Barker, a 2019 co-author, argues the rat levels place DMT in the normal range of the brain’s established transmitters (Barker, 2022). David Nichols argues the very small concentrations detected in the brain are not enough to produce psychoactive effects (Nichols, 2018). Both positions are about the same small body of rodent data. Evidence: unresolved. See also our INMT enzyme explainer and is DMT in the pineal gland?

The bottom line

The 2019 rat brain study is the best direct measurement of brain DMT we have, and it is a rat measurement. It showed DMT in living rat cortex at low nanomolar levels, independent of the pineal gland, rising after cardiac arrest in many but not all rats. It did not measure DMT in any human, did not show what DMT does in the brain, and did not show what happens when a person dies. Read with its limits, it is a reason to keep asking the question, not an answer to it.

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