A small clinical trial involving 34 people found that psychedelic-assisted therapy prompted a swift reduction in depressive symptoms that endured long after the drug had worn off, with some still feeling the benefits six months later.

Although preliminary, the results add to a growing body of evidence that psychedelic drugs, when coupled with psychotherapy, could help to alleviate depression in the millions of people worldwide who do not respond to existing antidepressants or therapies.

The trial, reported in Nature Medicine, focused on people with moderate to severe treatment-resistant depression. One half received a single 21.5mg dose of DMT infused into a vein over 10 minutes. The other half received a placebo infused the same way. All of the participants had psychotherapy and follow-up assessments.

Patients given DMT improved significantly compared with the placebo group, as measured by scores on a standard depression questionnaire, with the antidepressant effects lasting from three to six months.

In the second stage of the trial, all participants received a dose of DMT with therapy, but the researchers found no additional benefit in those who had two doses in total, suggesting a single dose may suffice. The trial was designed, funded and sponsored by Cybin UK, a neuropsychiatric firm.

The study follows a positive trial with psilocybin, the active ingredient in magic mushrooms, which has raised hopes for the drug being approved for treatment of depression later this year.

At doses used in the trials, DMT induces a shorter but more intense trip than psilocybin, with the experience lasting about 25 minutes compared with a couple of hours for psilocybin. That could make DMT-assisted therapy easier for clinics to deliver, although patients may need more support to recover from particularly intense DMT trips.

If regulators were to approve psychedelics for treating depression in the UK, researchers expect them to become available only through private clinics, said Dr James Rucker, a consultant psychiatrist at King’s College London who worked on the psilocybin trial.

Last year the Feilding commission was set up to guide the safe, ethical and equitable rollout of psychedelic-assisted therapies amid concerns that commercial pressures at private clinics could undermine safety, leading to patient harm.

Rucker said: “Quite how these drugs will fit in this world of financial austerity, stigma and opprobrium towards anything that has the word psychoactive in it, I don’t know. It’s interesting to be a part of, but I can’t call it.”