BOSTON, March 10 (UPI) -- Cocaine and amphetamines might cause slight mental impairments in abusers that persist for at least one year after discontinuing the drugs, research released Monday reveals.
However, experts outside the study said the findings were inconclusive and pointed out although cocaine has been widely abused for decades, impaired cognitive function is not seen routinely or even known to exist in former abusers.
"Overall, the abusers were impaired compared to non-abusers on the function of attention and motor skills," Rosemary Toomey, a psychologist at Harvard Medical School and the study's lead investigator, told United Press International.
Previous studies have yielded inconsistent findings on whether cocaine abuse led to long-term mental deficits. Some studies found deficits in attention, concentration, learning and memory six months after quitting. But a study of former abusers who were now in prison and had abstained from cocaine for three years found no deficit.
To help clarify these seemingly conflicting results, Toomey's team, in a study funded by the National Institute on Drug Abuse, identified 50 sets of male twins, in which only one had abused cocaine or amphetamines for at least one year. Amphetamine abusers were included because the drug is similar to cocaine and could have the same long-term effects on the body.
Most of the pairs were identical twins, meaning they share the exact same genetic pattern. This helps minimize the role biological differences could play in the findings and gives stronger support to the mental impairments being due to drug abuse.
The abusers, who averaged age 46 and had not used drugs for at least one year, scored significantly worse on tests of motor skills and attention, Toomey's team reports in the March issue of The Archives of General Psychiatry.
The tests all were timed, which indicates the abusers have "a motor slowing, which is consistent with what other investigators have found in other studies," Toomey said.
Still, the abusers' scores were within normal limits and they actually performed better on one cognitive test, called visual vigilance, which is an indication of the ability to sustain attention over time. This indicates the mental impairment is minor, Toomey said. "In real life, it wouldn't be a big impact on (the abusers') day-to-day functioning but there is a difference between them and their brothers," she said.
The finding is significant, she added, because given that the study subjects are twins and share the same biological make-up, they would be expected to have about the same mental status. This implicates the drug abuse as the cause of the mental impairment.
Among the abusers, the mental test scores largely did not vary in relation to the amount of cocaine or amphetamine used. However, on a few tests the abusers did score better with more stimulant use.
"The results seem to me to be inconclusive," Greg Thompson, a pharmacist at the University of Southern California's School of Pharmacy in Los Angeles, told UPI.
This is "because both twins are within a normal range (and) sometimes the cocaine-abusing twin did better than the non-abusing twin and sometimes not," Thompson said.
In addition, cocaine has been abused by millions of people, going back as far as the 1930s and before, he said. "You'd think you'd be seeing this as a significant clinical problem and we are not," he said.
Of more concern to Thompson is the effect stimulants such as Ritalin, which are used to treat attention deficit disorder, are having on children. "This would be a much bigger problem I would think if it's true stimulants impair cognitive function," he said.
"Before I'd worry about the 46 year-old abuser, I'd want to know about the 3 year old being treated for ADD (attention-deficit disorder)," Thompson said.
(Reported by Steve Mitchell, UPI Medical Correspondent, in Washington)