Cigarette smoking disrupts daily rest-activity patterns more than cannabis use

A new analysis of data from over 5,000 U.S. adults reveals that cigarette smoking has a more pronounced effect on rest-activity rhythms (RARs) than cannabis in cases where individuals use both substances. RARs reflect the health of your circadian system. A stable daily RAR pattern – activity during the day and rest at night—is a sign that your internal clock is functioning properly. The study showed that smokers had less predictable day-to-day activity patterns and weaker differences between their daytime and nighttime activity levels—both signs of an unhealthy rhythm. When people used both cigarettes and cannabis together, the disruption looked mostly like the effects of cigarette smoking alone, with cannabis showing only weak and inconsistent effects. This matters because disruption to RARs have been linked to serious health problems including heart disease, diabetes, and higher mortality rates, suggesting that throwing off your body's natural 24-hour clock may be one way smoking damages health.

Tobacco’s dominant impact on biological rhythms 

The study, “Rest-activity rhythms in individuals who separately or concomitantly use cannabis and cigarettes,” was conducted by OccHealthSci Senior Clinical Researcher Joey Hebl and Assistant Professor Nicole Bowles, Ph.D. in collaboration with Emory University Assistant Professor Danielle Wallace, Ph.D. The article was published in the journal Drug and Alcohol Dependence.

The research team examined rest-activity rhythms using objective actigraphy data from participants in the National Health and Nutrition Examination Survey (NHANES) collected between 2011 and 2014. They found that cigarette smoking was associated with less regular day-to-day activity patterns and reduced rhythm strength. They also found less fragmentation of daily activity compared to individuals who do not use cigarettes and/or cannabis. The findings suggest that cigarettes and cannabis have distinct effects on daily rest and activity rhythms and that when people use both substances, the effects look more like what would be expected from cigarette use alone. 

Tracking movement around the clock 

The research team analyzed accelerometer data that tracked participants' movements continuously for one week. They calculated several metrics including interdaily stability (how consistent activity patterns are from day to day) and intradaily variability (how fragmented rest and activity periods are within each day). Among the 5,129 participants aged 18-59, approximately 71% reported using neither substance, while 16% used only cigarettes, 6% used only cannabis, and 7% reported dual use. 

Irregular patterns among cigarette smokers 

Cigarette smoking, whether alone or combined with cannabis, was linked to decreased interdaily stability—meaning smokers had less regular day-to-day activity patterns. This association appeared strongest among infrequent smokers. The researchers speculate this could relate to social jetlag, or the misalignment between biological and social schedules that often occurs when people's smoking behavior is tied to social occasions rather than daily habits. 

Unexpected finding on activity fragmentation 

Interestingly, cigarette use was also associated with reduced intradaily variability, suggesting fewer transitions between rest and activity throughout the day. This counterintuitive finding contrasts with previous research and may reflect the complex effects that nicotine has on alertness, as well as the development of tolerance among individuals that regularly smoke cigarettes. Cannabis use alone showed weaker and less consistent effects on rest-activity patterns compared to cigarette use alone. 

Health implications of weakened rhythms 

The study also found that cigarette smokers—whether they used cannabis or not—showed weaker daily rhythms. This means there was less difference between how active they were during the day versus at night. Previous research has connected weaker daily rhythms to heart disease, diabetes, and higher death rates. This suggests that disrupting the body's natural daily patterns may be one way that smoking damages health. 

The study's limitations include its cross-sectional design, which prevents determining whether substance use causes rhythm disruption or vice versa. The researchers also relied on self-reported substance use data and lacked detailed information about cannabis consumption methods and timing, which have diversified considerably in recent years with legalization. 

As cannabis legalization continues to expand across the United States, understanding how different substances affect fundamental biological rhythms becomes increasingly important for public health. The researchers call for more detailed studies examining dose-dependent effects and the mechanisms underlying these rhythm disruptions. 

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This research was funded by the National Institutes of Health (NIHNHLBI K99HL166700, and K01 HL151745).