On the surface, the idea of receiving free samples at the doctor’s may seem beneficial to patients, but it turns out that is not the case. According to a new study, published in JAMA Dermatology, those free samples affect the way prescriptions are written and the consequences are costly.

Dr. Alfred Lane, from the Stanford University School of Medicine in Stanford, California headed up the study, which looked into prescribing habits in dermatologists across the United States to determine if there was a relationship between free samples and prescription costs. Researchers analyzed prescription writing habits of dermatologists nationwide in 2010 and compared that data with data collected from dermatological prescriptions written at Stanford. They focused specifically on prescriptions written for patients newly diagnosed with acne or rosacea.

What they found was that prescriptions written by dermatologists who gave out free samples tended to be written for brand-name drugs, which are more expensive than their generic counterparts. They discovered that dermatologists from the national database gave samples to roughly one in four patients, but only 21 percent of their patients received prescriptions for off-brand medications. The Sanford sample, in contrast, gave out no samples and had an 83 percent rate of generic brand prescriptions.

This appeared to be costing patients more than twice the amount in medication costs. The average cost per patient for prescriptions from Sanford’s data was around $200 while the national database showed an average cost per patient of $465.

While a clear causal relationship between free samples and more expensive treatment has not been conclusively isolated, experts increasingly agree that free samples should be a practice abandoned. In 2011, drug companies gave out $6.3 billion worth of free samples and based on the data available, researchers caution patients to be aware that this could dramatically impact their health care costs.