A digital illustration of an LSD molecule

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LSD could be approved for treating anxiety in the US as soon as 2027. This expectation comes after a landmark trial showed that a single dose of the psychedelic drug eased the mental health condition without severe or lasting side effects.

“It’s a milestone,” says Greg Cooper at University College London, who wasn’t involved in the trial. “It looks fairly likely that approval from the [US Food and Drug Administration] will happen in the next year or two,” he says. “That would set a precedent for approval elsewhere, such as the UK and Europe.”

“It seems likely that LSD will get FDA approved in the next 12 to 24 months,” says Jules Evans at the Challenging Psychedelic Experiences Project in the US, which researches difficult psychedelic experiences.

The trial was made up of people with moderate or severe anxiety who had tried a range of standard therapies. An approval will therefore probably apply to these groups, says Cooper. But people with milder anxiety would probably be able to access it at their doctor’s discretion, he says.

It is important that people don’t self-administer LSD for anxiety, says Cooper. “The results don’t mean that LSD is safe or effective to try at home,” he says. “An LSD [trip] can last for 6 to 12 hours and can sometimes cause intense fear, panic, confusion or frightening experiences.”

In the trial, Robert Barrow at Definium Therapeutics in New York and his colleagues recruited more than 200 adults across the US with moderate or severe generalised anxiety disorder. This affects almost 3 per cent of adults each year in the US and involves worrying excessively about a broad range of things, such as work and relationships.

The team tapered the participants off any anxiety medications before randomly assigning them to either take tablets adding up to a 100-microgram dose of LSD or placebo pills. A third group took 50 micrograms of LSD, a dose that has mind-altering effects, such as hallucinations, but didn’t substantially reduce anxiety in a prior trial. This was to overcome a common problem in psychedelic research, where participants can usually gauge whether they have taken a drug, impacting the placebo effect.

Three months after the dosing day, those on the higher dose had experienced a 9.8-point reduction in their anxiety levels, on average, out of 56 on a commonly used anxiety scale. In comparison, the placebo group’s score dropped by 4.7 points, on average, according to results announced by the company.

A reduction of 9.8 would noticeably improve someone’s quality of life, says Cooper. “It is certainly meaningful,” he says. None of the participants experienced severe or lasting side effects.

“In a disorder with high prevalence, high burden, high unmet need and no innovation in decades, a single dose of [LSD] has shown a rapid and durable effect,” said Barrow, speaking during a press briefing in August on a prior trial that found similar results when comparing only 100-microgram-dose LSD with placebo.

Unlike most trials into psychedelics for mental health conditions, the participants in the Definium ones weren’t offered psychotherapy in the weeks following the dosing day. Instead, they received limited psychological support on the day itself, although those already on psychotherapy were allowed to continue having it. “We stripped everything back and tried to show, to the extent we were able, the drug-only effect,” said team member Dan Karlin, also at Definium Therapeutics, at the briefing.

Adding regular psychotherapy would probably make the intervention more effective, says Evans. LSD is thought to work partly by boosting the brain’s ability to rewire itself and alter thought patterns, which psychotherapy also aims to do, he says.

In rare cases, LSD can cause psychosis and suicidal thoughts and behaviour. In the latest trial, only people without a history of these behaviours were included. “People were screened extremely carefully and given the drugs in an extremely well-controlled and safe and well-considered environment,” says Cooper. Such careful screening is needed, alongside long-term monitoring, if LSD is approved, says Evans.

Other psychedelic drugs like psilocybin and MDMA are already used to treat particularly severe cases of depression and post-traumatic stress disorder in some countries, such as Australia and Switzerland.

Need a listening ear? UK Samaritans: 116123; US 988 Suicide & Crisis Lifeline: 988; hotlines in other countries.