Heavy and light drinkers show differences in biological markers of the internal processes that regulate the 24-hour sleep/wake cycle. The study findings, reported in Alcoholism: Clinical and Experimental Research, may have implications for the clinical management of patients seeking treatment for heavy drinking. Previous studies have shown that later circadian timing, manifesting as a preference for evening (“night owl”) rather than morning (“lark”) activity, is associated with increased alcohol consumption. However, research into the association between alcohol use and biological markers of circadian timing was lacking. Two such markers are DLMO (dim light melatonin onset—considered the gold standard circadian phase marker) and PIPR (the post-illumination pupil response—a measure of activity of photoreceptors in the eye that are a key influence on circadian timing). In the latest study, researchers compared sleep, DLMO-related measures, and photoreceptor responsivity in heavy and light drinkers.