Acute dose-dependent effects of lysergic acid diethylamide in a double-blind placebo-controlled study in healthy subjects
Study design
The study used a double-blind, placebo-controlled, crossover design with six experimental test sessions to investigate the responses to (i) placebo, (ii) 25 µg LSD, (iii) 50 µg LSD, (iv) 100 µg LSD, (v) 200 µg LSD, and (vi) 200 µg LSD 1 h after ketanserin administration (40 mg). Block randomization was used to counterbalance the different dosing conditions. The washout periods between sessions were at least 10 days. The study was conducted in accordance with the Declaration of Helsinki and International Conference on Harmonization Guidelines in Good Clinical Practice and approved by the Ethics Committee of Northwest Switzerland (EKNZ) and Swiss Federal Office for Public Health. The study was registered at ClinicalTrials.gov (NCT03321136).
Participants
Sixteen healthy subjects (eight men and eight women; mean age ± SD: 29 ± 6.4 years; range: 25–52 years) were recruited by word of mouth or an advertisement that was posted on the web market platform of the University of Basel. Mean body weight was 69 kg and 78 and 60 kg in male and female participants, respectively. Accordingly, doses/body weight of LSD were 1.3-fold higher in men than women. All of the subjects provided written informed consent and were paid for their participation. Drug administration timing did not consider the menstrual cycle in females for practical reasons. Four women used a hormonal contraceptive and one was menopausal. Exclusion criteria were age <25 years or >65 years, pregnancy (urine pregnancy test at screening and before each test session), personal or family (first-degree relative) history of major psychiatric disorders (assessed by the Semi-structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, 4th edition, Axis I disorders by a trained psychiatrist), the use of medications that may interfere with the study medications (e.g., antidepressants, antipsychotics, and sedatives), chronic or acute physical illness (e.g., abnormal physical exam, electrocardiogram, or hematological and chemical blood analyses), tobacco smoking (>10 cigarettes/day), lifetime prevalence of illicit drug use >10 times (except for Δ9-tetrahydrocannabinol), illicit drug use within the last 2 months, and illicit drug use during the study period (determined by urine drug tests). The participants were asked to consume no more than 10 standard alcoholic drinks/week and have no more than one drink on the day before the test sessions. Six participants had previously used LSD (1–3 times), eight participants had used methylenedioxymethamphetamine (MDMA) (1–5 times), ten participants had previously used a stimulant, including methylphenidate (four participants, 1–2 times), amphetamine (six participants, 1–3 times), and cocaine (two participants, 1–2 times), and one participant had smoked opium (once). Six participants had never used any illicit drugs with the exception of cannabis. Substance use histories are shown in Table S1 in the Supplementary Methods online. Drug of abuse tests performed once during the screening and once during the study in each subject were negative.
Study drugs
LSD base (>99% purity; Lipomed AG, Arlesheim, Switzerland) was administered as an oral solution that was produced according to good manufacturing practice in units that contained 100 or 25 µg LSD in 1 ml of 96% ethanol [20]. The exact analytically confirmed LSD content (mean ± SD) of the 25 and 100 µg formulations was 25.7 ± 0.57 µg (n = 9 samples) and 98.7 ± 1.6 µg (n = 9 samples), respectively. Stability of the formulation for longer than the study period was documented in an identically produced previous batch [20]. One microgram of LSD base that was used in the present study corresponded to 1.25 µg LSD tartrate that was used recreationally and in other studies [9, 21]. Ketanserin was obtained as the marketed drug Ketensin (20 mg, Janssen-Cilag, Leiden, NL) and encapsulated with opaque capsules to ensure blinding. Placebo consisted of identical opaque capsules that were filled with mannitol. A double-dummy method was used. The subjects received two capsules and two solutions in each session: (i) two placebo capsules and placebo/placebo solutions, (ii) two placebo capsules and 25 µg LSD/placebo solutions, (iii) two placebo capsules and 25 µg LSD/25 µg LSD solutions, (iv) two placebo capsules and 100 µg LSD/placebo solutions, (v) two placebo capsules and 100 µg LSD/100 µg LSD solutions, and (vi) two ketanserin capsules and 100 µg LSD/100 µg LSD solutions. At the end of each session and at the end of the study, the participants were asked to retrospectively guess their treatment assignment.
Study procedures
The study included a screening visit, six 25 h test sessions (each separated by at least 10 days), and an end-of-study visit. The sessions were conducted in a calm hospital room. Only one research subject and one investigator were present during each test session. The test sessions began at 7:45 a.m. A urine sample was taken to verify abstinence from drugs of abuse, and a urine pregnancy test was performed in women. The subjects then underwent baseline measurements. Ketanserin (40 mg) or placebo was administered at 8:00 a.m. LSD or placebo was administered at 9:00 a.m. The outcome measures were repeatedly assessed for 24 h. Standardized lunches and dinners were served at 1:30 p.m. and 6:00 p.m. respectively. The subjects were never alone during the first 16 h after drug administration, and the investigator was in a room next to the subject for up to 24 h. The subjects were sent home the next day at 9:15 a.m.
Subjective drug effects
Subjective effects were assessed repeatedly using visual analog scales (VASs) [12, 13] 1 h before and 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, and 24 h after drug administration. VASs were assessed each time LSD blood concentrations were measured to allow for PK–PD modeling. The Adjective Mood Rating Scale (AMRS) [22] was used 1 h before and 3, 6, 9, 12, and 24 h after drug administration. The 5 Dimensions of Altered States of Consciousness (5D-ASC) scale [23, 24] was used as the primary outcome measure and was administered 24 h after drug administration to retrospectively rate peak drug effects. Mystical experiences were assessed 24 h after drug administration using the States of Consciousness Questionnaire [25, 26] that includes the 43-item Mystical Effects Questionnaire (MEQ43) [25], 30-item Mystical Effects Questionnaire (MEQ30) [27], and subscales for “aesthetic experience” and negative “nadir” effects. Subjective effects measurements are described in detail in Supplementary Methods online.
Autonomic and adverse effects
Blood pressure, heart rate, and tympanic body temperature were repeatedly measured [28]. Adverse effects were assessed 1 h before and 12 and 24 h after drug administration using the list of complaints [29].
Plasma BDNF levels
Plasma BDNF levels were measured at baseline and 6, 12, and 24 h after drug administration using the Biosensis Mature BDNF Rapid ELISA Kit (Thebarton, Australia) [30].
Plasma LSD concentrations
Blood was collected into lithium heparin tubes. The blood samples were immediately centrifuged, and the plasma was subsequently stored at −80 °C until analysis. Plasma concentrations of LSD and O–H–LSD were determined by ultra-high-performance liquid chromatography tandem mass spectrometry with a lower limit of quantification of 5 pg/ml [20].
Pharmacokinetic analyses and pharmacokinetic–pharmacodynamic modeling
Pharmacokinetic (PK) parameters were estimated using a one-compartment model with first-order input, first-order elimination, and no lag time in Phoenix WinNonlin 6.4 (Certara, Princeton, NJ, USA) [20]. The predicted concentrations of LSD were then used as an input to the pharmacodynamic (PD) model by treating the PK parameters as fixed and using a sigmoid maximum effect model in the classic PK/PD link model module in WinNonlin [20]. The time to onset, time to maximal effect, time to offset, and effect duration were assessed for the model‐predicted “any drug effect” VAS effect-time plots after LSD administration using a threshold of 10% of the maximum individual response using Phoenix WinNonlin 6.4.
Data analysis
Peak (Emax and/or Emin) or peak change from baseline (ΔEmax) values were determined for repeated measures. The values were then analyzed using repeated-measures analysis of variance, with drug as the within-subjects factor, followed by the Tukey post hoc test. The data were analyzed using Statistica 12 software (StatSoft, Tulsa, OK, USA). The criterion for significance was p < 0.05. No correction for multiple testing was applied.
