Nightcap or Nightmare? The Science Behind Alcohol's Impact on Sleep
By Sam Chapman, Student Network Representative from St. Francis Xavier University
Alcohol and Sleep Patterns: A Review of Mechanisms and Consequences
Sleep is a fundamental component of physical and mental health, underpinning processes of memory consolidation, emotional regulation, and physiological recovery (Irwin, 2015). The use of alcohol is often perceived as a quick route to sleep. However, mounting evidence indicates that even moderate drinking can disrupt sleep architecture and impair the restorative functions of sleep. This post reviews how alcohol affects sleep onset, stages, and long-term sleep quality, explores the physiological mechanisms involved, and outlines the health implications.
BoldHealth Inc. (2024, October 28). How alcohol affects sleep: Tips for better rest in recovery [Image].
Regarding sleep architecture, alcohol has a pronounced effect on rapid eye movement (REM) sleep and non-REM deep sleep, specifically slow-wave sleep (SWS). High doses of alcohol significantly reduce the percentage of REM sleep and delay the onset of the first REM period (Ebrahim et al., 2013). More recently, even low doses (≤0.50 g/kg) of alcohol (approx. two standard drinks) have been shown to reduce REM sleep duration in healthy adults (Gardiner et al., 2024). At the same time, some studies report an increase in SWS during the first half of the night following alcohol ingestion (Ebrahim et al., 2013). However, the initial deeper sleep appears deceptive: as alcohol is metabolized, a “rebound” of wakefulness, lighter sleep stages and fragmented sleep dominate the latter half of the night (American Addiction Centers, 2023).
Disrupted sleep due to alcohol has acute and chronic consequences. Immediately, impaired REM and fragmented sleep reduce the restorative benefits of sleep: individuals may wake feeling unrefreshed, experience impaired cognitive performance, and be at elevated risk of mood disturbance. In the long term, consistent alcohol-related sleep disruption is linked to increased risk of insomnia, cardiovascular disease, metabolic dysfunction, and worsened mental health outcomes (American Addiction Centers, 2023).
Clinically, alcohol should not be regarded as a sleep aid. Even a seemingly moderate evening drink can significantly degrade sleep quality. For patients presenting with sleep complaints, clinicians should assess alcohol use habits, including timing (drinks close to bedtime are especially problematic) and quantity. Minimizing alcohol intake in the hours leading up to bedtime, and ideally reducing overall consumption, are crucial strategies for improving sleep hygiene and promoting resilience.
References
American Addiction Centers. (2023). Alcohol and insomnia: How alcohol affects sleep. https://www.americanaddictioncenters.org/alcohol/risks-effects-dangers/insomnia
Bold Health Inc. (2024, October 28). How alcohol affects sleep: Tips for better rest in recovery [Image]. https://boldhealthinc.com/how-alcohol-affects-sleep-tips-for-better-rest-in-recovery/
Ebrahim, I. O., Shapiro, C. M., Williams, A. J., & Fenwick, P. B. (2013). Alcohol and sleep I: Effects on normal sleep. Alcoholism: Clinical and Experimental Research, 37(4), 539–549. https://doi.org/10.1111/acer.12006
Gardiner, C., Weakley, J., Burke, L. M., Roach, G. D., Sargent, C., Maniar, N., Huynh, M., Miller, D. J., Townshend, A., & Halson, S. L. (2025). The effect of alcohol on subsequent sleep in healthy adults: A systematic review and meta-analysis. Sleep medicine reviews, 80, 102030. https://doi.org/10.1016/j.smrv.2024.102030