Ashwagandha typically takes 4 to 8 weeks of daily use to produce measurable reductions in cortisol levels, though some studies have detected lower salivary cortisol in as little as 30 days. This isn’t a supplement that works after a single dose. The cortisol-lowering effect builds gradually with consistent use, and the strongest clinical evidence points to the 8-week mark as the timeline where results become statistically significant across multiple trials.
What the Clinical Trials Show
A systematic review and meta-analysis published in BJPsych Open, which pooled data from multiple controlled studies, found a significant reduction in cortisol levels after 8 weeks of ashwagandha supplementation. The effect was consistent enough across studies to reach strong statistical significance, alongside reductions in perceived stress scores.
Some results appear sooner. One clinical trial of 60 adults in Florida measured salivary cortisol after just 30 days. Participants taking as little as 225 mg per day of a root and leaf extract already showed lower cortisol levels than those on placebo. So while 8 weeks is the most reliable benchmark, changes can begin within the first month for some people.
Across the broader research, a 2021 systematic review of seven trials (491 total participants) found that ashwagandha taken for 6 to 8 weeks significantly reduced serum cortisol compared to placebo, while also improving sleep, fatigue, and self-reported stress and anxiety. No major trial has demonstrated a cortisol reduction from a single dose or even a few days of use. This is a cumulative effect, not an acute one.
How Ashwagandha Affects Cortisol
The exact mechanism isn’t fully understood, but researchers have identified several plausible pathways. The active compounds in ashwagandha, called withanolides, appear to interact directly with the receptors your body uses to detect and respond to stress hormones. One compound, withaferin A, binds to these receptors in a way that dampens the inflammatory signaling cascade that can keep cortisol elevated.
There’s also an indirect route. Ashwagandha has mild calming and sleep-promoting properties, partly through its effects on GABA, a brain chemical that reduces nervous system activity. Better sleep and lower baseline anxiety mean your stress response system doesn’t fire as often or as intensely, which gradually brings cortisol down. This layered mechanism helps explain why the effect takes weeks to fully develop: your body’s stress response system needs time to recalibrate.
Dosages Used in Research
Clinical trials have tested a fairly wide range of doses, but most fall between 225 mg and 600 mg per day using standardized extracts. The 30-day Florida trial found cortisol reductions at 225 mg daily, while the larger body of 6-to-8-week studies generally used doses in the 300 to 600 mg range. Higher doses don’t necessarily work faster. The 225 mg group in that trial actually showed lower cortisol than the 400 mg group, suggesting that more isn’t always better and that extract standardization matters as much as raw milligrams.
If you’re choosing a supplement, look for a standardized extract with a specified withanolide percentage. The most commonly studied branded extracts include KSM-66 (root-only, typically 5% withanolides) and Sensoril (root and leaf). The specific extract matters because raw ashwagandha powder and concentrated extracts deliver very different amounts of active compounds at the same weight.
Morning or Evening Dosing
There’s no strong clinical evidence that taking ashwagandha at a specific time of day produces better cortisol results. If you’re using it primarily for stress management during the day, morning makes sense. If you’re drawn to its calming and sleep-promoting effects, taking it in the evening works well too. Some people experience mild stomach discomfort, which can be reduced by taking it with food or shifting it to the evening. The most important factor is consistency: taking it at whatever time helps you remember to take it daily.
Who Should Avoid Ashwagandha
Ashwagandha is not appropriate for everyone. It should be avoided during pregnancy and breastfeeding. People with autoimmune diseases or thyroid disorders are advised against using it, since it can stimulate immune activity and alter thyroid hormone levels. It may also increase testosterone, which makes it unsuitable for anyone with hormone-sensitive prostate cancer.
If you take medications for diabetes, high blood pressure, seizures, or thyroid conditions, ashwagandha can interact with them. The same applies to immunosuppressants and sedatives. Because ashwagandha has calming properties, stacking it with other sedating substances can amplify drowsiness beyond what you’d expect from either one alone.
Setting Realistic Expectations
The honest picture is that ashwagandha produces a modest, gradual reduction in cortisol over weeks of daily use. It’s not a dramatic overnight fix. In the meta-analysis data, the cortisol reductions were statistically significant but not enormous. For someone with chronically elevated stress, that moderate shift can translate into noticeably better sleep, less anxiety, and reduced fatigue. For someone whose cortisol is already in a normal range, the effects may be subtle.
Most people in clinical trials were self-reported “stressed adults,” not people with clinical cortisol disorders like Cushing’s syndrome. If you suspect a medical condition is driving abnormally high cortisol, ashwagandha isn’t a substitute for proper evaluation. But for garden-variety chronic stress, the evidence supports a real, if gradual, benefit starting around the 4-week mark and solidifying by week 8.