Trait mindfulness and personality characteristics in a microdosing ADHD sample: a naturalistic prospective survey study

Attention deficit hyperactivity disorder (ADHD) in adults is prevalent and characterised by inattention, hyperactivity and/or impulsivity. Adults with ADHD typically score lower on measures of trait mindfulness and show a distinct personality profile compared with neurotypical adults, most reliably lower conscientiousness and higher neuroticism. Anecdotal and survey reports indicate that some adults with ADHD self-administer repeated sub‑hallucinogenic doses of psychedelics (microdosing, MD) to ameliorate symptoms, and previous studies in general or healthy samples have reported MD‑associated increases in mindfulness and alterations in personality traits, but findings have been inconsistent and prospective data in ADHD populations are lacking. Haijen and colleagues designed the present study to examine whether 4 weeks of self‑initiated MD is associated with changes in trait mindfulness and Big Five personality traits in adults diagnosed with ADHD or in adults without a diagnosis who nevertheless showed clinically elevated ADHD symptoms. The main hypotheses were that total mindfulness would increase after MD, and that conscientiousness, extraversion, agreeableness and openness would increase while neuroticism would decrease. The investigators also explored whether concurrent use of conventional ADHD medication or the presence of psychiatric comorbidities moderated any MD‑related changes.

This was a prospective naturalistic survey study. Adults who had either received an ADHD diagnosis or reported ADHD symptoms severe enough to interfere with daily life were recruited online via a microdosing information website and enrolled between November 2020 and July 2021. Participants completed a baseline survey 1–3 days before initiating MD on their own initiative, and follow‑up surveys exactly 2 and 4 weeks after baseline. Daily short surveys recorded whether participants microdosed each day, and, if so, the substance and dose (self‑reported). The Ethics Review Committee at Maastricht University approved the study. Eligibility screening used the Conners' Adult ADHD Rating Scale (CAARS‑S:SV) at baseline; respondents without an ADHD diagnosis whose CAARS T‑scores were all below 65 were excluded from analyses. Demographic, psychiatric/medical diagnosis and prior psychedelic use data were collected at baseline. The main outcomes were trait mindfulness measured with the 15‑item Five Facet Mindfulness Questionnaire (FFMQ‑15; five three‑item subscales and a total score) and personality traits measured with the 10‑item Big Five Inventory (BFI‑10; five two‑item scales). The CAARS was collected at all time points but only baseline CAARS scores were used in the present analyses. Statistical analysis relied on linear mixed models (LMMs) with restricted maximum likelihood estimation to accommodate missing data, and Akaike's information criterion was used to choose covariance structures. Separate LMMs tested time effects (baseline, 2 weeks, 4 weeks) on the FFMQ‑15 total and subscales and on each BFI‑10 trait. The investigators repeated key models including a covariate for recent mindfulness practice (dichotomised as practiced within the past 7 days versus not) and tested interactions with medication use (concurrent prescribed ADHD medication during the study versus none) and comorbidity (ADHD plus ≥1 other diagnosis versus ADHD only or no ADHD). Pairwise comparisons were Bonferroni‑corrected and effect sizes were reported as partial eta squared (ηp2).

Of 247 respondents who completed the baseline survey, 14 were excluded (two for implausibly fast responses, 12 non‑diagnosed respondents with CAARS T‑scores <65), leaving 233 participants at baseline; 66 and 44 participants provided data at the 2‑ and 4‑week time points respectively. At baseline the sample was 50.2% female (n = 117), 82.8% resided in Europe (n = 193) and 73% had tertiary education (n = 170). Prior psychedelic experience was common (82%, n = 191). A current psychiatric, neurological or physical diagnosis was reported by 71.2% (n = 166); ADHD was the most frequent diagnosis (68.2%, n = 159), and among those with ADHD, 54.1% (n = 86) reported at least one comorbid diagnosis. One third of participants with ADHD (n = 53) were using prescribed ADHD medication during the study. Mindfulness (FFMQ‑15): LMMs indicated a main effect of time on the FFMQ‑15 total score. Pairwise tests showed higher total mindfulness at 2 weeks versus baseline (Δ2W–0W = 3.62, p < 0.001) and at 4 weeks versus baseline (Δ4W–0W = 5.97, p < 0.001); total scores were also higher at 4 weeks than at 2 weeks (Δ4W–2W = 2.35, p = 0.043). Across the five mindfulness facets, observation increased at 4 weeks versus baseline (Δ4W–0W = 0.75, p = 0.008; model F (2,119.1) = 3.10, p = 0.049, ηp2 = 0.05). Description increased at 2 weeks (Δ2W–0W = 0.81, p = 0.002) and 4 weeks (Δ4W–0W = 1.42, p < 0.001) compared to baseline (AR1 covariance; effect remained after adjusting for recent mindfulness). Acting with awareness scores rose at 2 and 4 weeks versus baseline (Δ2W–0W = 0.64, p = 0.029; Δ4W–0W = 1.01, p = 0.005; unstructured covariance), but this time effect was no longer significant when recent mindfulness was added as a covariate. Non‑judging of inner experience showed a robust time effect (F ≈ 13.40, p < 0.001, ηp2 = 0.19) with increases at 2 weeks (Δ2W–0W = 1.04, p < 0.001) and 4 weeks (Δ4W–0W = 1.94, p < 0.001); scores at 4 weeks were higher than at 2 weeks (Δ4W–2W = 0.90, p = 0.036). An interaction between time and medication use was observed for non‑judging: participants using conventional medication alongside MD had lower non‑judging scores at 2 weeks compared with those only MD (β = −2.32, p = 0.002). Non‑reactivity increased at 2 and 4 weeks versus baseline (Δ2W–0W = 0.73, p = 0.011; Δ4W–0W = 1.05, p = 0.007) but the time effect lost significance after adjusting for recent mindfulness. Personality (BFI‑10): For conscientiousness a time effect was reported (AR1 covariance; F (2,136.3) = 3.77, p = 0.025, ηp2 = 0.05) with higher scores at 4 weeks versus baseline (Δ4W–0W = 0.40, p = 0.002); however, this effect did not survive correction for multiple testing. Neuroticism decreased over time (ante‑dependence covariance; F (2,60.8) = 7.19, p = 0.002, ηp2 = 0.19): scores were lower at 4 weeks than at baseline (Δ4W–0W = −0.60, p < 0.001) and lower at 4 weeks than at 2 weeks (Δ4W–2W = −0.34, p = 0.014); the 2‑week versus baseline difference did not reach significance (Δ2W–0W = −0.26, p = 0.056). Comorbidity had a main effect on neuroticism, with higher scores for those with comorbid diagnoses at baseline and 2 weeks but not at 4 weeks. Extraversion showed a time effect with higher scores at 2 weeks versus baseline (Δ2W–0W = 0.24, p = 0.039) but this did not survive multiple‑comparison correction. Agreeableness and openness showed no significant changes over time. Across outcomes, inclusion of the recent mindfulness covariate and the relatively small sample at later time points affected some findings, and the investigators used REML to handle missing data in the LMMs.

Haijen and colleagues interpret their findings as indicating that self‑initiated MD over a 4‑week period was associated with increases in trait mindfulness and a reduction in neuroticism in adults with ADHD or clinically elevated ADHD symptoms. Specifically, the mindfulness facets description and non‑judging of inner experience continued to show significant increases after controlling for recent mindfulness practice, whereas the other three facets were no longer robust to that adjustment. Changes observed in conscientiousness and extraversion were small and did not survive correction for multiple testing, and agreeableness and openness remained unchanged. The investigators situate these results within prior MD literature: the increase in mindfulness aligns with several earlier reports but contrasts with at least one prospective MD study that found no change. They suggest that MD effects might be more detectable in clinical samples because baseline scope for improvement is larger. The observed decrease in neuroticism is consistent with some previous prospective MD studies; differences between studies may depend on participants' prior psychedelic experience, as some evidence suggests inexperienced microdosers might show different neuroticism responses. The authors note that baseline scores for mindfulness and certain personality traits in the present ADHD sample differed from general population norms, which may influence change trajectories and create potential ceiling or floor effects. Key limitations acknowledged by the authors include the naturalistic, non‑experimental design which precludes firm causal attribution and prevents control over drug identity and dose; reliance on self‑reported substance and dose data; a high attrition rate leading to small samples at follow‑up (n = 44 at 4 weeks) and potential bias if participants with adverse experiences dropped out. The loss of some effects when adding covariates may reflect reduced statistical power or overfitting. For future research the authors recommend placebo‑controlled trials with standardised dosing, longer follow‑up to assess durability of effects, development of ecologically valid laboratory measures sensitive to low doses, and comparisons of MD with non‑pharmacological mindfulness interventions or combined approaches. They also highlight preparation and prior psychedelic experience as potentially important moderators, noting the clinical relevance of understanding whether inexperienced participants are at risk of adverse changes such as increased neuroticism.