Cannabis use in middle age 'doesn't lead to mental decline'
Scientists said casual cannabis users performed better on memory test
They said this could be because they generally had a higher education level than non-users
Middle-aged adults whose memories have grown hazy can't blame smoking cannabis for their forgetfulness, according to researchers.
Scientists from King's College, London, found occasional pot use could actually improve concentration levels although they stressed that long-term use could be harmful.
The study, carried in the American Journal of Epidemiology, tested the mental function and memory of nearly 9,000 Britons at age 50 and found that those who had used illegal drugs as recently as in their 40s did just as well, or slightly better, on the tests than peers who had never used drugs.
One in four adults in the research said they had used cannabis in the past
Cannabis was by far the most common indulgence for the participants – who were surveyed at age 42 about current or past drug use, then tested at age 50 – with six per cent saying they had used it in the past year, while one-quarter said they had ever used it.
Between three and eight per cent said they had ever used other harder drugs including amphetamines, LSD, hallucinogenic mushrooms, cocaine and ecstasy.
'Overall, at the population level, the results seem to suggest that past or even current illicit drug use is not necessarily associated with impaired cognitive functioning in early middle age,' said lead researcher Dr Alex Dregan.
'However, our results do not exclude possible harmful effects in some individuals who may be heavily exposed to drugs over longer periods of time.'
A small subset of participants who said they had ever been treated for their drug use, which could suggest heavy or addicted drug use, did not fare as well cognitively at 50, but there were too few of them to draw meaningful conclusions, the study authors noted.
The cannabis plant: Dr Halpern said the study did not rule out the possibility of lasting negative effects from heavy, prolonged drug use
Dr Dregan's team used data on 8,992 42-year-olds participating in a UK national health study, who were asked if they had ever used any of 12 illegal drugs. Then, at the age of 50, they took standard tests of memory, attention and other cognitive abilities.
Overall, the study found, there was no evidence that current or past drug users had poorer mental performance. In fact, when current and past users were lumped together, their test scores tended to be higher.
But that advantage was small, the researchers said, and might just reflect another finding – that people who'd ever used drugs generally had a higher education level than non-users.
'In a Western population of occasional drug users, this is what you'd expect to see,' said John Halpern, a psychiatrist at Harvard Medical School.
'In some ways, this is not surprising. The brain is resilient.'
Though some studies have found that drugs like cannabis and cocaine may cloud thinking, memory and attention in the short term, the current findings support the notion that those effects may be temporary, Dr Dregan's team said.
Dr Halpern noted that work focusing on people who have smoked pot regularly for years showed that once they stop the drugs, their deficits on cognitive tests improve after a month.
Still, he said this should not be taken as an endorsement of drug use, noting that the current study did not rule out the possibility of lasting negative cognitive effects from heavy, prolonged drug use.
classed as a sedating and hallucinogenic drug. Some users find it makes
them feel relaxed and happy in the short term. However, the drug can cause feelings of anxiety, suspicion, panic and paranoia. It can also increase the risk of developing psychosis.
It is a Class B drug in the UK, which means it is illegal to possess or supply.