More than half of patients who report “weekend-only” drug use end up expanding their drug use to weekdays, too, suggesting that primary care clinicians should monitor patients who acknowledge recreational drug use, according to a new study by Boston University School of Public Health (SPH) and School of Medicine researchers.

The study, published in the journal “Annals of Family Medicine” and led by Judith Bernstein, professor of community health sciences at SPH, recommends that clinicians use “caution in accepting recreational drug use as reassuring,” and that they conduct “continued episodic monitoring” of patients who report weekend-only drug use.

The study followed 483 patients at Boston Medical Center who reported using drugs in the previous month and who completed a follow-up visit six months later. Of those who reported weekend-only use initially, 19.2 percent retained that pattern six months later, while 54 percent were using drugs on other days of the week.

Drugs most commonly used included marijuana, cocaine, and opioids.

“These findings suggest the importance of periodic monitoring of ‘recreational’ drug use,” the study said. “A single-question standardized screen can be used to elicit necessary information.”

Bernstein said in a news release the findings indicate that weekend-only drug use “frequently progresses into daily use, and warrants continued monitoring” by clinicians.

“The real message of this paper is a monitoring message,” she said. Primary care providers “are in a position to support positive behavioral change, as well as to address increases in drug-use intensity as an integral part of their role.”

Illegal drug use among primary care patients is estimated at 5 percent to 8 percent, but often goes undetected. Any drug use may have an impact on disease processes and the effectiveness of prescribed medication, the study stated.