Cannabis is widely considered to be a stress reliever – at least for some – but there's new evidence that it might actually have the opposite effect when used regularly.Researchers from Oregon State University wanted to take a closer look at the relationship between cannabis and stress after earlier studies had hinted that the drug may raise stress levels rather than lower them.The team looked specifically at the hypothalamic-pituitary-adrenal (HPA) axis, the body's main stress responder. Made up of connections between the brain and kidneys, it controls the release of the stress-related hormone cortisol.We all have a cortisol awakening response of some kind when we wake up. (Westend61/Getty Images)As shown by results now published in Cannabis by the researchers, those who use cannabis regularly tend to have higher levels of cortisol when waking up in the morning."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," says behavioral neuroscientist Anita Cservenka.The study involved 39 frequent cannabis users and 43 controls who indulged in cannabis use rarely or not at all. Over two weekdays, the participants were asked to collect saliva swabs right after waking up, 30 minutes later, and at 9pm that evening.These saliva samples were then scanned for cortisol, and the volunteers also filled out questionnaires about their perceived stress levels, sleep quality, and mental health symptoms.In particular, the researchers wanted to look at the cortisol awakening response (CAR), which is the jump in cortisol levels in the body in the morning. It's thought to be a natural response used to prep the body for the day ahead."CAR is the cortisol rise that all people experience in the morning, peaking around 30 minutes after they wake up," says Cservenka.