High cortisol at night is one of the most common and least-discussed causes of poor sleep quality. If you struggle to fall asleep, wake up during the night with a racing mind, or feel wired but tired in the evenings, elevated evening cortisol is a likely contributor. This article explains the science behind why cortisol disrupts sleep, how the feedback loop develops, and what the evidence shows about managing it.
How Cortisol and Sleep Are Connected
Cortisol follows a precise 24-hour rhythm. In a healthy system it peaks within 30 to 45 minutes of waking, then declines steadily across the day before reaching its lowest point in the early hours of sleep, when slow-wave recovery is most concentrated. When this rhythm is disrupted, sleep suffers. The disruption runs in both directions: poor sleep raises cortisol, and high cortisol suppresses sleep quality.
What High Cortisol at Night Does to Sleep
Cortisol is a glucocorticoid that promotes arousal, raises blood glucose, increases heart rate, and suppresses the parasympathetic nervous system. These are appropriate responses in an acute stress situation. In the evening, these same mechanisms prevent the conditions sleep requires.
A study published in Sleep demonstrated that exogenous cortisol administration in the evening significantly reduced slow-wave sleep and increased nighttime awakenings. The effect was dose-dependent: higher cortisol, less deep sleep. Separately, research in the Journal of Clinical Endocrinology and Metabolism found that HPA axis hyperactivity is among the most consistent biological findings in primary insomnia.
The Feedback Loop
Poor sleep itself raises cortisol. Research in Sleep found that even one night of sleep restriction elevated evening cortisol levels the following day. This creates a self-reinforcing cycle: stress raises cortisol, cortisol disrupts sleep, poor sleep raises cortisol further. Over time this blunts the growth hormone release, immune function, and tissue repair that depend on undisturbed slow-wave sleep.
Ashwagandha and the HPA Axis
Ashwagandha (Withania somnifera) has the most evidence of any adaptogen for HPA axis modulation. A randomised, double-blind, placebo-controlled trial in Medicine found that 300mg of Ashwagandha root extract twice daily produced significant reductions in morning cortisol and improvements in Pittsburgh Sleep Quality Index scores. A second trial using KSM-66 extract, published in the Indian Journal of Psychological Medicine, found a 27.9 percent reduction in serum cortisol over 60 days.
Reishi, L-Theanine and Parasympathetic Support
Reishi triterpenes have demonstrated inhibitory effects on sympathetic nervous system activity in preclinical research. L-Theanine, an amino acid found in green tea, increases alpha-brain wave activity and modulates GABA and glutamate levels. A meta-analysis in Nutrients found consistent reductions in subjective stress and anxiety across clinical trials. Both are included in the AE·ORA REST Reishi Relax Gummies specifically because they support the parasympathetic conditions that allow cortisol to decline naturally in the evening.
Frequently Asked Questions
Quick answers to the questions readers most often ask.
What causes high cortisol at night?
Common causes include chronic psychological stress, high training volumes without adequate recovery, irregular sleep schedules, excessive caffeine late in the day, and blue-light exposure in the evening (which suppresses melatonin and maintains cortisol). Some individuals have underlying HPA axis dysfunction.
How do I know if high cortisol is disrupting my sleep?
Signs include difficulty falling asleep despite feeling tired, waking between 2am and 4am with a racing mind, feeling wired in the evening, and waking unrefreshed despite sufficient hours. A salivary cortisol test (four-point diurnal test) can confirm elevated evening cortisol.
Does ashwagandha lower cortisol?
Multiple randomised controlled trials have found that ashwagandha root extract (particularly KSM-66 extract) reduces serum cortisol by 14 to 28 percent over 60 days of supplementation. Effects accumulate over several weeks rather than occurring acutely.
Can cortisol cause insomnia?
Yes. Elevated cortisol in the evening is one of the most consistently identified biological features in primary insomnia. Cortisol promotes arousal and suppresses the slow-wave sleep stages that drive physical and cognitive recovery. The relationship is bidirectional: insomnia also raises cortisol.
How long does it take for ashwagandha to reduce cortisol?
Clinical trials have found measurable cortisol reductions after 4 to 8 weeks of consistent daily supplementation with standardised ashwagandha extract. The effect is not acute. Consistent nightly use is required for cortisol-reducing benefits to accumulate.
References
This article references peer-reviewed clinical research. Click through to read the source studies on PubMed.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
