The study, conducted by Oregon State University scientists, was published in the journal Cannabis.

Stress is one of the main reasons people report using cannabis, and it is also associated with problematic patterns of use. Although cannabis can provide temporary relief from stress, the researchers say frequent use over time could potentially interfere with the biological systems that regulate the stress response.

Led by Anita Cservenka of the OSU College of Liberal Arts, the research is among the relatively few studies to investigate how frequent cannabis use relates to the hypothalamic pituitary adrenal axis, the major neuroendocrine system responsible for coordinating the body's response to stress.

Cannabis Use Has Risen Sharply Among Young Adults

The findings come as cannabis use has become increasingly common among young adults in the United States. Twenty-nine percent of adults ages 19 to 30 report using cannabis during the previous 30 days, a rate that has nearly doubled over the past 15 years.

More than 10% of people in that age group report using cannabis at least 20 times within a 30-day period. According to the researchers, that percentage is more than twice what it was 15 years ago.

Cservenka cautions that the findings do not establish that frequent cannabis use causes higher cortisol levels upon waking. They also do not show that elevated morning cortisol causes people to use cannabis more frequently.

"We would need to study the same groups of people over a longer period of time to understand any cause-and-effect relationship, but we think this provides an important starting point," she said.

Why Cortisol Matters

Cortisol is a hormone made by the adrenal glands. Hormones act as chemical messengers that help regulate many processes throughout the body.

Often called the "stress hormone" because the body releases it in response to pressure, cortisol plays several essential roles. It helps the body fight infection, maintain blood pressure, and regulate blood sugar and metabolism.

In the short term, cortisol helps the body cope with stressful situations. However, cortisol levels that remain elevated for long periods can have negative health effects and have been associated with greater risks of anxiety, depression, and heart disease.

Measuring the Morning Cortisol Response

Cservenka and OSU colleagues Julia Donner and Alexia Obrochta focused on what is commonly known as CAR, or the cortisol awakening response.

"CAR is the cortisol rise that all people experience in the morning, peaking around 30 minutes after they wake up," Cservenka said.

Researchers calculate CAR by measuring cortisol immediately after a person wakes and then measuring it again 30 minutes later. The first measurement is subtracted from the second. The resulting difference is considered an indicator of how the body prepares itself to handle the demands and stressors of the coming day.

The researchers found that the size of this morning cortisol increase was similar in cannabis users and nonusers. The important difference appeared at the starting point. People who frequently used cannabis already had more cortisol circulating in their bodies when they woke up.

A Potential Biological Signal of Problematic Cannabis Use

"Our research suggests cortisol levels upon awakening may serve as a neurobiological marker of problematic cannabis use, and that connection needs to be investigated further," Cservenka said. "Earlier studies by other researchers found CAR to be blunted in frequent cannabis users, but we didn't replicate that finding, which suggests there is a lot of nuance that could be related to analytic strategies and sample characteristics."

The difference from previous research highlights how complicated the relationship between cannabis use and the body's stress system may be. Factors involving study populations and the methods researchers use to analyze cortisol patterns could help explain why different studies have produced different results.

Even so, Cservenka said it is reasonable to consider the possibility that frequent cannabis users may experience disruptions in their normal daily stress rhythms. Such changes could potentially contribute to a feedback cycle in which a poorly regulated stress system encourages further cannabis use.

Oregon State University, the OSU Center for the Humanities, and the OSU College of Liberal Arts funded the research.