Psychedelic drugs may find a place in the treatment of mental illness, say researchers who injected LSD into people and monitored their brains.
LSD is banned in New Zealand and many countries but researchers in Britain, including one now working in New Zealand, got approval to run a study in 20 people who had used psychedelic drugs before.
Some were given injections of 75 micrograms of LSD and others placebo injections of saline solution.
The LSD dose was "about the equivalent of a street tab, a strong one," said Dr Suresh Muthukumaraswamy, of the University of Auckland School of Pharmacy, a researcher on the study.
Two types of MRI scan were done to measure blood flow and magnetic fields in the brain were tested.
"Results revealed marked changes in brain blood flow, electrical activity, and network communications patterns that correlated strongly with the drug's hallucinatory and other consciousness-altering properties," the five-country research team say in an article in the Proceedings of the National Academy of Sciences.
Dr Muthukumaraswamy said they found segregation of certain brain networks was reduced after LSD was administered; brain activity became less structured.
"This wasn't a study of people with mental illnesses but the potential application is that some of those brain networks that become desegregated are known to be overactive in certain mental illnesses, whereas this drug or some drug with similar chemistry could be used to break down those [areas of] over-segregated network activity in the brain.
"There are particular networks which are overactive ... in depression and potentially in addiction."
He hoped the study might help to ease restrictions on research on LSD, a drug that was widely investigated until the 1960s, after it had become popular among recreational users.
He said LSD was safe to use in research - the risk to recreational users was that it could lead people to do dangerous things because of altered thinking, "the same as with alcohol".
What is LSD
• Lysergic acid diethylamide
• A commonly-used recreational drug
• Many potential effects, including euphoria, hallucinations, distorted thinking, confusion, paranoia
• Illegal. Possession can attract up to six months imprisonment, $1000 fine or both.