Ashwagandha typically lowers cortisol by roughly 12% to 16% compared to placebo, based on clinical trial data. That translates to an average reduction of about 1.16 micrograms per deciliter in blood cortisol levels. Some older claims floating around the internet put the number as high as 30%, but the more rigorous meta-analyses point to a moderate, not dramatic, effect.
What the Clinical Trials Actually Show
A systematic review and meta-analysis of ashwagandha studies found a statistically significant drop in serum cortisol compared to placebo groups, with a mean difference of 2.58 micrograms per deciliter across pooled trials. Individual studies vary quite a bit depending on the dose, the extract used, and how stressed participants were at baseline. People with higher starting cortisol levels tend to see a larger absolute drop, which is partly why percentage estimates range so widely across different trials.
The clinical significance of these reductions is still debated. A 12% to 16% cortisol drop is real and measurable, but cortisol fluctuates naturally throughout the day by far more than that. Morning cortisol can be three to four times higher than evening levels in a healthy person. So while ashwagandha nudges the average downward, it’s not fundamentally reshaping your stress hormone profile.
How Ashwagandha Affects Cortisol
The active compounds in ashwagandha, called withanolides, are naturally occurring steroids that appear to dampen activity in the body’s central stress response system. This system connects the brain to the adrenal glands (the small organs on top of your kidneys that produce cortisol). When you’re under chronic stress, this system stays activated and keeps cortisol elevated. Withanolides seem to dial that signaling down, reducing how much cortisol your adrenals pump out.
One case report raised a concern worth knowing about: long-term ashwagandha use was linked to suppressed adrenal function in at least one individual. Whether this represents a risk for typical users at standard doses isn’t clear yet, but it’s a reminder that “lowers cortisol” isn’t inherently positive if the suppression goes too far or continues indefinitely.
Dosage That Produces Results
Clinical trials have used doses ranging from 125 mg to 1,250 mg per day of ashwagandha extract, with study durations from 30 to 90 days. According to the NIH Office of Dietary Supplements, the cortisol-lowering benefits appeared to be greater at doses of 500 to 600 mg per day compared to lower doses. That said, one trial found that even 225 mg per day of a concentrated extract lowered salivary cortisol after 30 days, and another found results with just 300 mg per day of a standardized root extract over 90 days.
The withanolide concentration matters more than the raw milligram count on the label. A 300 mg capsule standardized to contain 15 mg of withanolides can outperform a larger dose of a less concentrated product. This is why the specific extract matters.
Differences Between Common Extracts
Three branded extracts dominate the market, and they’re not interchangeable. KSM-66 is a root-only extract designed to preserve the natural ratios of compounds found in ashwagandha root. It has the broadest base of clinical research across stress, cognition, and physical performance. Sensoril uses both leaf and root material and is particularly high in compounds called glycowithanolides, which are associated with calming and sleep-promoting effects. Shoden is a full-spectrum root and leaf extract containing at least 35% withanolides, far higher than the other two, which means it shows effects at lower doses.
If your primary goal is cortisol reduction specifically, all three have supporting evidence. Sensoril tends to appear in studies focused on stress and relaxation. KSM-66 shows up more often in studies measuring a broader range of outcomes including physical endurance. Shoden offers the highest withanolide concentration per milligram.
How Long Before It Works
You won’t see cortisol changes overnight. The shortest trial to show measurable cortisol reduction lasted 30 days at 225 mg per day. Most studies run 60 to 90 days, and longer durations generally produce more consistent results. If you’ve been taking ashwagandha for two weeks and feel nothing, that’s expected. Plan on at least four to six weeks of daily use before drawing conclusions.
Stress perception often improves before cortisol numbers change. Several trials show participants reporting less anxiety within two to four weeks, while the measurable cortisol drop takes longer to reach statistical significance. This could reflect other mechanisms ashwagandha has on mood and neurotransmitter activity beyond cortisol alone.
Effects Beyond Cortisol
Cortisol and testosterone have an inverse relationship in the body. When cortisol stays chronically elevated, testosterone production tends to suffer. By lowering cortisol, ashwagandha may create conditions that allow testosterone to rise. One study of overweight men found a 15% increase in testosterone after eight weeks of supplementation. Another trial in young men doing resistance training showed testosterone increases five times greater than the placebo group, though that dramatic difference partly reflects how exercise amplifies the effect.
These hormonal shifts are most relevant if you’re chronically stressed. Someone with already-normal cortisol and healthy testosterone is unlikely to see the same magnitude of change. The supplement appears to work by correcting stress-driven imbalances rather than pushing hormones beyond their normal range.
Who Should Avoid It
The National Center for Complementary and Integrative Health specifically recommends against ashwagandha for people with autoimmune diseases or thyroid disorders. Because ashwagandha can influence thyroid hormone levels and immune function, it may worsen conditions like Hashimoto’s thyroiditis, Graves’ disease, lupus, or rheumatoid arthritis.
Ashwagandha can also interact with medications for diabetes, high blood pressure, seizures, and thyroid conditions, as well as sedatives and immunosuppressants. Because it may raise testosterone levels, people with hormone-sensitive prostate cancer should avoid it entirely. If you’re scheduled for surgery, stop taking it beforehand, as it can affect sedation and blood pressure responses.
How Cortisol Is Measured in Studies
If you’re trying to verify ashwagandha’s effect on your own cortisol, it helps to know what researchers actually measure. Most studies use either blood (serum) cortisol or saliva cortisol. Salivary testing is considered a reliable proxy for blood levels and is easier to do at home or in field settings. Some direct-to-consumer lab services now offer at-home saliva cortisol kits, which could let you track your own levels before and during supplementation.
Timing your sample matters enormously. Cortisol peaks within 30 to 45 minutes of waking and drops throughout the day. To get a meaningful comparison, you’d need to test at the same time of day, under similar conditions, before and after several weeks of consistent use.