Cortisol and Insomnia: Does High Evening Cortisol Keep You Awake?

If you lie awake at night with a racing mind, it is tempting to blame cortisol. Wellness feeds often describe "high nighttime cortisol" as the hidden cause of insomnia and suggest teas, supplements, or "adrenal" protocols to bring it down. There is a real scientific story behind the idea, but it is more tentative and more tangled than the headlines suggest.

Start with the settled physiology. In healthy people, cortisol follows a daily rhythm: it rises in the early morning, peaks shortly after waking, and declines through the day to its lowest levels in the evening and early part of sleep. That evening dip is thought to be part of the body's normal wind-down. If the stress system stays active when it should be quieting, it makes sense that sleep could suffer, and that is the basic logic behind the evening-cortisol theory.

The best-known study supporting it is a 2001 sleep-laboratory study by Vgontzas and colleagues in the Journal of Clinical Endocrinology and Metabolism. The team compared 11 young adults with chronic insomnia to 13 good sleepers over 24 hours. Across the full day, the insomnia group had somewhat higher cortisol, though that overall difference was borderline and did not clear the usual threshold for statistical significance. The largest elevations were in the evening and the first half of the night, and they were greater in those whose sleep was most disrupted when measured in the lab. The authors interpreted this as a sign of hyperarousal of the stress system, not simply a result of lost sleep.

There are important limits. That study was small, measured only a single 24-hour period, and in young adults, so it cannot tell us what happens in the wider population. Later research, including a 2010 review by Balbo, Leproult, and Van Cauter in the International Journal of Endocrinology, describes a two-way relationship: stress-system activity can disturb sleep, and disturbed or shortened sleep can in turn alter cortisol patterns, with studies showing mixed results depending on the sample and the timing of measurement. In other words, research suggests a link, but it does not show that high evening cortisol is the cause of insomnia, and not everyone with insomnia has high levels at all.

This matters because of what is sold. Supplements and drinks marketed to "lower nighttime cortisol" have not been shown in good trials to treat insomnia, and a single saliva or blood result taken at home is a poor basis for deciding that cortisol is your problem. Meanwhile, treatments with solid evidence target the sleep problem itself. The American Academy of Sleep Medicine's 2021 clinical practice guideline on behavioral and psychological treatments recommends cognitive behavioral therapy for insomnia, or CBT-I, as a core approach, using techniques such as consistent sleep timing, stimulus control, and sleep restriction guided by a clinician.

So what is proven and what is trend? Well established: cortisol normally falls in the evening, and stress can interfere with sleep. Suggested but unsettled: some people with chronic insomnia show higher evening and early-night cortisol, and the direction of cause is unclear. Trend and marketing: the claim that high cortisol is the root of most insomnia and that a supplement or tea will reset it. If sleep trouble lasts more than a few weeks, a doctor can check for sleep apnea, medication effects, mood conditions, and other treatable causes.