LSD may help to lower anxiety in patients with life-threatening diseases, according to a small pilot study.

The study, published Tuesday in The Journal of Nervous and Mental Disease, is the first to examine the therapeutic use of lysergic acid diethylamide (LSD) in more than 40 years.

LSD is a semisynthetic psychedelic drug known to produce a range of psychological effects, including increased sensory perception, synesthesia and enhanced mental imagery. The drug was made illegal in the United States in 1966, and is considered a controlled substance under Canada's Controlled Drugs and Substances Act.

The double-blind, randomized trial involved 12 participants who had a range of illnesses including terminal cancer, Parkinson's disease and Celiac disease.

The patients were given LSD during two supervised therapy sessions. Eight of the patients were assigned to receive a larger dose of LSD and four of the patients were assigned to receive a lower dose.

The study found a significant reduction in anxiety among the participants after two LSD-assisted psychotherapy sessions.

The study's lead author, Dr. Peter Gasser, said the results show that LSD can be safely administered during supervised therapy sessions.

"The study was a success in the sense that we did not have any noteworthy adverse effects," he said in a statement. "All participants reported a personal benefit from the treatment, and the effects were stable over time."

Two months after the therapy sessions, anxiety levels in the patients who had received the full doses of LSD had improved by about 20 per cent. By comparison, anxiety levels in the patients who had received lower doses of LSD had worsened. These results lasted up to a year after the therapy sessions.

One of the study participants said he had an emotional experience with the drug.

"My LSD experience brought back some lost emotions and ability to trust, lots of psychological insights, and a timeless moment when the universe didn’t seem like a trap, but like a revelation of utter beauty,” Peter, an Austrian participant, said in a statement.

The trial participants were treated in Switzerland from 2008 to 2012. During the therapy sessions, they were told to focus "inward" to follow their "personal process of perception, emotion and cognition."

The participants were screened for anxiety symptoms before they were given LSD to determine a baseline measure of anxiety. They were screened again, one week, two months and one year after the therapy sessions had ended.

The authors note that the results are not conclusive due to the small sample size. They argue that more research into the use of LSD-assisted therapy is warranted.

"This study is historic and marks a rebirth of investigation into LSD-assisted psychotherapy," Dr. Rick Doblin of the Multidisciplinary Association for Psychedelic Studies (MAPS) said in a statement. "The positive results and evidence of safety clearly show why additional, larger studies are needed."

During the 1950s and 60s, researchers explored the use of LSD in conjunction with psychotherapy. However, research came to a halt when the drug was made illegal.

The study was partially funded by MAPS – a non-profit research group that examines the medical, legal and cultural contexts for the use of psychedelics and marijuana.