Paula Ross-Durow at the University of Michigan said if a teen was prescribed a drug, parents might leave the drugs available.
Ross-Durow analyzed data on 230 Michigan eighth- and ninth-graders who said they had been prescribed medications.
"About three-quarters of those teens said that they had unsupervised access to their medications," Ross-Durow said in a statement.
Ross-Durow said parents need to dispense the medication and keep them locked up -- otherwise, teens could use them when not medically needed, sell them to other teens and visiting teens couldn't steal them.
The study was published in the Journal of Adolescent Health.
Texas principal bans speaking Spanish, stirs controversy
Ron Burgundy interviews Peyton Manning on SportsCenter