One professor wants to know if your coffee fix could lead to a drug problem.   Professor Stacey Sigmon discovered in her study with colleague Roland Griffiths that caffeine users are more subject to the positive effects of d-amphetamines, according to an article from the College of Medicine.   In a double blind, outpatient lab study with healthy adult volunteers, participants were given caffeine through capsule form, Sigmon said.   “In phase one, the patients chose either a red or blue pill; one was a placebo and one had caffeine, and repeated daily,” she said. “They chose which pill provided them with better effects and then were divided into two groups: choosers and non-choosers.”   In phase two, the study was repeated with d-amphetamine replacing caffeine, Sigmon said. It is a psychomotor stimulant that has similar effects to cocaine.   The choosers were more subject to the good effects of the d-amphetamine than the non-choosers, according to the study.   “It was interesting because there was no difference in age, ethnicity or gender between the choosers and non-choosers,” Sigmon said.   Caffeine is the most widely used drug in the world and is highly acceptable, she said. The vast majority of caffeine users don’t continue towards harder drug use.   “All I think it means is how caffeine users are more subject to the good effects of caffeine,” she said.  “Whether or not they are going to go on to other substance use, that would require another study.”   However, Sigmon said she does have concerns about the high levels of caffeine in energy drinks.   “There are huge doses of caffeine, as well as new formulations of that caffeine and other vitamins and ingredients,” she said. “Nobody really knows the effects. Young adults are the target marketing groups for energy drinks.”