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CORVALLIS, Ore. - Methamphetamine users who described themselves as impulsive were more likely to have started taking the drug at an earlier age, a study of more than 150 users showed.

Both attentional and motor impulsivity were linked to early meth use, even when accounting for total years of use. On average, people who use methamphetamine start at about age 22.

"It's really unclear if impulsivity is a contributor or a consequence of early methamphetamine use; I think it's both," said Anita Cservenka, an assistant professor in the School of Psychological Science at Oregon State University and co-author of the recent study in the journal Addictive Behaviors.

"Impulsivity is highly related to the number of years of using methamphetamine, specifically in men. Our findings suggest that impulsivity likely both contributes to using this substance and increases as a result of using it."

The National Institute on Drug Abuse funded the study, and Lara A. Ray of UCLA was the corresponding author. The researchers looked at 157 meth users' scores on the Barratt Impulsiveness Scale, a widely used self-reporting measure of impulsive personality traits.

Those in the study sample were between 18 and 50 years old, reported using meth in the last 30 days, and reported not using any other substances other than alcohol, tobacco or marijuana. The subjects were free of major mental or physical health problems and were not seeking treatment for their meth use.

The Barratt Impulsiveness Scale is broken into multiple types of impulsivity, some of which include attentional and motor impulsivity. Attentional impulsiveness has been defined as an inability to focus attention or concentrate. Motor impulsiveness refers to a tendency to act on whims.

About 1 percent of 12^th-graders report having used meth at least once, and more than 6 percent of people 26 and older have used meth in their lifetime.

"One possibility is that meth users are self-medicating," Cservenka said. "If they have difficulty paying attention, they may try to use meth to perhaps improve their attentional ability, as amphetamines are clinically prescribed for this purpose."

Illicitly manufactured and distributed, methamphetamine is a toxic, strong, highly addictive central nervous system stimulant. Using it can cause disturbed sleep patterns, hyperactivity, nausea, delusions, aggressiveness, irritability, confusion, anxiety and hallucinations.

"Methamphetamine use is such a big burden on the individual and also at the societal level," Cservenka said. "We pay a lot for users' health care because meth use impairs both psychosocial function and physical health. These results suggest that if we find individuals during adolescence who show elevated symptoms of impulsivity or a lack of inhibitory control, they may be individuals we want to target for early intervention.

Cservenka says longitudinal studies - tracking subjects over time - are needed to better determine if impulsivity is a trigger for early meth use.

"Because this was a cross-sectional study, we can't say that impulsivity led to meth use," she said. "We can only suggest that perhaps impulsivity might be a trait that individuals should pay attention to in at-risk youth, especially when it comes to late adolescence or young adulthood, when most meth use is initiated.

"We can only see the complete picture if we track adolescents at an early age and then follow them into young adulthood to understand what risk factors contribute to starting using a substance like meth. Impulsivity may be one of them, but there are likely a number of other risk factors.