NEW YORK (Reuters Health) - Middle aged adults whose memories have grown hazy can't blame occasional pot smoking or other light illicit drug use, new research suggests.
In a study of nearly 9,000 Britons whose memory and mental function were tested at age 50, researchers 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.
When the participants were surveyed at age 42 about current or past drug use, marijuana was by far the most common indulgence: six percent said they had used it in the past year, while one-quarter said they had ever used it.
Other drugs they were asked about included amphetamines, LSD, hallucinogenic mushrooms, cocaine and ecstasy -- with anywhere from three percent to eight percent of study participants saying they'd ever used those drugs.
While the researchers found no significant difference between drug users and non-users in cognitive tests, they also stress that this doesn't mean illegal drugs harm no one.
According to one expert not involved in the study, the findings should not be seen as an endorsement of drug use.
"We're trying to understand where the harms are, and where they aren't," said Dr. John H. Halpern, a psychiatrist at Harvard Medical School and McLean Hospital in Belmont, Massachusetts, who has studied the potential cognitive effects of drug use.
The current findings suggest that for the occasional drug user at mid-life, there are unlikely to be lasting cognitive consequences, according to Halpern.
"In a Western population of occasional drug users, this is what you'd expect to see," he told Reuters Health.
"In some ways," Halpern said, "this is not surprising. The brain is resilient."
Still, he pointed out, the study could not clearly separate "drug users from abusers."
The British researchers say it's possible that people who use drugs frequently or for years could see lingering effects on their mental function.
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 age 50, but there were too few of them to draw meaningful conclusions, the study authors note.
"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, of King's College London.
"However," he told Reuters Health in an email, "our results do not exclude possible harmful effects in some individuals who may be heavily exposed to drugs over longer periods of time."
For the study, which appears in the American Journal of Epidemiology, Dregan's team used data on 8,992 42-year-old adults participating in a UK national health study, who were asked whether they had ever used any of 12 illegal drugs.
Then, at the age of 50, participants 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 say, and might just reflect another finding -- that people who'd ever used drugs generally had a higher education level than non-users.
Though some studies have found that drugs like marijuana and cocaine may cloud thinking, memory and attention in the short term, the current findings support the notion that those effects may be temporary, according to Dregan's team.
Other research suggests that too. Halpern pointed to work focused on people who've smoked pot regularly for years: once they stop the drug, researchers have found, their deficits on cognitive tests improve after a month.
But Halpern agreed that the current results do not rule out the possibility of lasting negative cognitive effects from heavy, prolonged drug use.
There are, of course, other reasons to avoid illegal drugs. As an example, Halpern noted that cocaine can trigger a stroke. And one of the possible consequences of a stroke is long-term cognitive impairment.
SOURCE: bit.ly/xGsK5t American Journal of Epidemiology, online December 21, 2011.