Dose-dependent pharmacokinetics and acute effects of intravenous bolus N,N-dimethyltryptamine: double-blind, randomized versus open-label dose-escalation administration study in healthy participants

DMT is a short-acting serotonergic psychedelic that can produce very rapid and intense effects when given intravenously as a bolus. Earlier work suggested that this route may have therapeutic promise, including in depressive disorders, but the pharmacokinetics, dose-response relationship, acute subjective effects, and the influence of blinding and expectancy had not been characterised systematically for bolus dosing. In addition, bolus administration appeared to be less well tolerated than continuous infusion in some previous studies, raising questions about how dose, context, and the design of administration shape the acute experience. Erne and colleagues set out to compare the dose-dependent pharmacokinetics and acute effects of intravenous bolus DMT in healthy participants across two administration contexts: a double-blind, randomised, placebo-controlled, crossover design and an open-label dose-escalation design. The study also aimed to assess whether stepwise within-session dose escalation could improve tolerability and help inform dosing for future clinical studies of DMT.

The researchers conducted two independent study arms in healthy adults who were screened for medical and psychiatric exclusion criteria. In total, 36 participants were enrolled: 20 in the randomised arm and 16 in the open-label dose-escalation arm. Participants could choose which arm to join. The randomised arm included equal numbers of men and women and used a double-blind, placebo-controlled, crossover design. Participants received placebo and 5 mg, 10 mg, 15 mg, and 20 mg DMT in random order within a single test session. The open-label arm used stepwise escalation, beginning with placebo and then increasing DMT in 5 mg increments from 5 mg up to a maximum of 25 mg, with participants deciding after each dose whether to continue. DMT was administered intravenously as a bolus over 45 seconds in 20 ml solution. The researchers used a 1-hour washout between boluses, based on the short elimination half-life of DMT and prior evidence that acute effects subside within about 20-30 minutes. In the dose-escalation arm, the interval could be extended by up to 30 minutes after an intense or negative experience. The protocols were approved by the relevant ethics and regulatory bodies, and the study was registered at ClinicalTrials.gov. Outcome assessments included repeated measures of subjective drug effects, autonomic effects, adverse effects, and plasma DMT concentrations over 55 minutes after each bolus. Subjective effects were measured with simple verbal rating scales and with validated psychedelic questionnaires, including the 3D-ASC, the PES48, and the NDE-C scale. Blood pressure, heart rate, and adverse complaints were also recorded. Plasma DMT and metabolites were quantified by high-performance liquid chromatography-tandem mass spectrometry, and pharmacokinetic parameters were estimated using non-compartmental methods. For the randomised arm, peak values or peak change from baseline were analysed using analysis of variance with dose as the within-subject factor, followed by Tukey post hoc testing. Between-arm comparisons used the Wilcoxon rank-sum test, but the authors note that these comparisons were exploratory because the study was powered for within-subject dose comparisons rather than between-group analyses.

In the randomised arm, DMT produced very rapid and dose-dependent subjective effects. Significant effects were observed from 5 mg onwards compared with placebo. Peak effects occurred within the first 1-3 minutes after administration and then declined quickly, with subjective effects fully subsiding within 12-30 minutes. A ceiling effect for peak subjective intensity was observed at 15 mg, indicating that higher doses did not increase peak ratings proportionally. However, the duration of effect increased with dose, and the area under the effect-time curve for “any drug effect” was higher at 20 mg than at 15 mg. Positive ratings were generally much higher than negative ones, but the 15 mg and 20 mg doses produced more “bad drug effect” and “fear” than lower doses. Psychedelic measures showed similar dose-response patterns. The 10 mg, 15 mg, and 20 mg doses produced pronounced psychedelic experiences, whereas 5 mg caused only mild changes. Most 3D-ASC and PES48 subscales reached a ceiling at 15 mg in the randomised arm, with no clear additional increase at 20 mg. Higher doses also increased negative experiences, including anxious ego dissolution, anxiety, impaired control and cognition, and distressing experience. Autonomic and adverse effects included headache, impaired concentration, weakness, and palpitations. One participant required psychiatric follow-up after later reporting anxiety and panic attacks that began shortly after the study session; these symptoms resolved within 2 months, recurred 3 months later, and the participant was subsequently treated with psychotherapy and escitalopram. Pharmacokinetically, DMT concentrations rose and fell very rapidly. In the randomised arm, mean peak plasma concentrations were 11 ng/ml, 20 ng/ml, 37 ng/ml, and 45 ng/ml after 5 mg, 10 mg, 15 mg, and 20 mg, respectively, with peak concentrations reached at roughly 2.3-2.7 minutes. The initial plasma half-life was about 6.1-6.8 minutes during the first 20-30 minutes after dosing. A slower decline was suggested from 30 to 55 minutes, but the authors say the later phase could not be estimated reliably because of limited sampling. The concentration-effect relationship suggested no acute pharmacological tolerance with repeated hourly boluses. At 5 mg and 10 mg, subjective effects closely tracked plasma levels, whereas at 15 mg and 20 mg, the effects remained near peak for longer despite declining concentrations, consistent with a ceiling effect rather than tolerance. In the open-label dose-escalation arm, a ceiling effect appeared only at 20 mg and 25 mg, and repeated dosing did not reduce ratings, again indicating no acute tolerance. Blinding was only partly successful. Most conditions were correctly identified at the end of the study, once all doses could be compared, but immediate post-dose guesses were often incorrect for 10 mg to 20 mg, typically mistaken for the next higher or lower dose. Placebo and 5 mg were guessed correctly in more than 80% of cases after administration. Compared with the open-label dose-escalation arm, subjective effects were generally lower at equivalent doses. Ratings of “good drug effect” were similar between arms, but “bad drug effect” and fear were higher in the randomised arm. Several psychedelic subscales were also higher in the randomised arm. In contrast, the dose-escalation arm showed dose-proportional increases in positive effects up to 25 mg, with no ceiling effect until higher doses. Ten of 16 participants escalated to 25 mg, including three psychedelic-naive participants.

The authors interpret the study as showing that intravenous bolus DMT produces extremely rapid, short-lived, and dose-dependent psychedelic effects in healthy participants, with peak subjective effects reached within about 1-3 minutes. They emphasise that the peak intensity reached a ceiling around 15 mg in the blinded randomised arm, while the effect duration continued to increase with dose. They also state that the pharmacokinetic findings support a very rapid elimination profile, with an initial half-life of about 6-7 minutes, consistent with prior work. The discussion positions these findings alongside earlier studies, noting that the rapid onset and short duration are broadly consistent with previous intravenous DMT research. The authors suggest that differences across studies, such as delayed peaks in one earlier report, may relate to injection volume and the speed at which the drug reaches the circulation. They also compare bolus administration with continuous infusion, arguing that bolus dosing appears less tolerable, mainly because of its intensity and abruptness. Despite the intense and sometimes anxiety-provoking effects at higher doses, all participants in the randomised arm completed the within-day protocol, which the authors present as evidence that the experience remained acceptable overall. A major theme in the discussion is the absence of acute tolerance with intermittent bolus dosing. The authors report no clockwise hysteresis, no decline in response across repeated doses, and no order effects, and they contrast this with moderate acute tolerance reported for continuous DMT infusion. They suggest that tolerance depends more on the dosing pattern than on a specific property of DMT itself, and they mention possible mechanisms such as receptor desensitisation and downstream signalling changes during sustained exposure. The authors also interpret the comparison between blinded and open-label dosing as evidence that blinding, expectancy, and perceived control strongly shape the psychedelic experience. In the randomised arm, placebo and the 5 mg dose were often identified correctly, illustrating how difficult it is to maintain blinding with a psychoactive drug. In the open-label dose-escalation arm, participants reported lower subjective intensity and markedly fewer negative effects at the same doses, which the authors attribute to preparation, reassurance, and the ability to anticipate and control dose increases. They argue that this context may have reduced anxiety and made higher doses more tolerable. The authors note several strengths, including the crossover, placebo-controlled design; the direct comparison of two administration contexts; the use of standardised psychometric measures; and the inclusion of both men and women. They also acknowledge important limitations. Participants self-selected into study arms rather than being randomised, which may have introduced bias; for example, the dose-escalation group included more cautious and less psychedelic-experienced individuals. They also note that the dose-escalation arm may have been biased towards those who tolerated the drug better, because some participants stopped early. Finally, the between-arm comparison was exploratory because the study was not powered for those differences. The discussion closes by framing dose escalation as a practical approach to improving tolerability and individualising dosing in future DMT studies, including potential therapeutic applications.