Bloodshot eyes can be a sign of drug use. The blood vessels on the surface of the eye dilate in response to the use of certain drugs, making the eyes appear red.
Review Date 8/26/2017
Updated by: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.