One dose of LSD beat placebo by 5.1 points on a 56-point anxiety scale

The gap between the 100-microgram arm and placebo is 5.1 points ^[1], about 9 per cent of the scale's range ^[3]. Put another way, the placebo response accounts for roughly 48 per cent of the improvement recorded in the drug arm ^[2]. Greg Cooper of University College London, who was not involved in the trial, said of the 9.8-point drop: "It is certainly meaningful" ^[12][2].

Robert Barrow of Definium spoke at an August press briefing about an earlier trial that compared 100 micrograms with placebo alone and found similar results. He said the disorder has high prevalence, high burden and high unmet need, with no innovation in decades, and that a single dose of LSD had shown a rapid and durable effect ^[14]. Generalised anxiety disorder affects almost 3 per cent of US adults each year ^[8].

In psychedelic research, participants can usually gauge whether they got the drug, and that distorts the placebo comparison. So the team gave one group 50 micrograms, a dose that produces hallucinations but did not substantially reduce anxiety in a prior trial ^[10]. New Scientist does not report the three-month anxiety score for that group. Until it appears, how much of the 5.1-point gap survives against an active comparator is an open question.

"We stripped everything back and tried to show, to the extent we were able, the drug-only effect," said Dan Karlin of Definium at the same briefing ^[16]. Adding regular psychotherapy would probably make the intervention more effective, said Jules Evans of the Challenging Psychedelic Experiences Project. LSD is thought to work partly by boosting the brain's ability to rewire itself and alter thought patterns ^[17].

Three months is where the reported follow-up ends, so these results cannot say how long a single dose holds, or when a patient would need another. Cooper said participants "were screened extremely carefully and given the drugs in an extremely well-controlled and safe and well-considered environment" ^[19]. Evans said that screening, along with long-term monitoring, would be needed if the drug is approved ^[20]. Cooper also said: "The results don't mean that LSD is safe or effective to try at home" ^[21]. A trip "can last for 6 to 12 hours and can sometimes cause intense fear, panic, confusion or frightening experiences", he said ^[22].

The 2027 date is an expectation. The efficacy numbers came from a company announcement ^[11], and the timeline comes from Cooper, who was not involved in the work, and from Evans ^[2][4]. Cooper said US approval "would set a precedent for approval elsewhere, such as the UK and Europe" ^[3]. Psilocybin and MDMA are already used for particularly severe depression and post-traumatic stress disorder in some countries, including Australia and Switzerland ^[23].