Psilocybin was given to 36 volunteers and most found the experience to be spiritually uplifting.

"Surrender is intensely powerful. To 'let go' and become enveloped in the beauty of -- in this case music -- was enormously spiritual," said one volunteer.

After a year, they were asked how they now felt about their experience -- the vast majority still felt the benefits.

"This is a truly remarkable finding," said Dr Roland Griffiths, a neuroscientist at Johns Hopkins University in Baltimore.

"Rarely in psychological research do we see such persistently positive reports from a single event in the laboratory."

"This gives credence to the claims that the mystical-type experiences some people have during hallucinogen sessions may help patients suffering from cancer-related anxiety or depression and may serve as a potential treatment for drug dependence."

Research into psychedelics has attracted a great deal of controversy over the years, especially due to worries about the mental health of participants.

But Dr Griffiths believes that the subjects of the psilocybin trial did not experience any lasting harm.

"While some of our subjects reported strong fear or anxiety for a portion of their day-long psilocybin sessions, none reported any lingering harmful effects, and we didn't observe any clinical evidence of harm," he said.

In fact, over half of the participants considered the session to be one of the most significant events of their lives.

"We have people saying these eight hours in the lab are among the most meaningful in their lives," Dr Griffiths said.

"Some rank it alongside births and deaths of loved ones."