Ashwagandha: The Evidence File

What ashwagandha is

Withania somnifera is an evergreen shrub grown across tropical and subtropical parts of Asia, Africa, and Europe. The Sanskrit name is usually translated from the smell of the root. It's been used for thousands of years in Ayurvedic practice as an adaptogen, which the NIH Office of Dietary Supplements defines loosely as something that increases a person's ability to resist or adapt to stressors in nonspecific ways.

The compounds that get the attention are withanolides, a group of steroidal lactones. Lab work has associated them with anti-inflammatory and antioxidant activity. The plant also carries alkaloids, sitoindosides, and a long list of other constituents that shift depending on plant part and extraction method.

One detail matters more than it looks. The ODS states it plainly: the chemical composition of the root and the leaf differ.

Most commercial supplements contain root extract. Some contain extracts of both root and leaf. That isn't a marketing footnote. Two bottles both labeled ashwagandha can carry materially different chemistry, and a trial result from one can't be transferred to the other.

Why the extract name matters more than the herb

In the trials below you'll see named extracts: KSM-66, Sensoril, Shoden, Prolanza, NooGandha. Those names aren't branding noise. Each one has a different plant part, a different extraction process, and a different withanolide standardization.

Here's what the trials the ODS summarizes actually used:

• KSM-66 is a root-only extract. The Chandrasekhar trial used a high concentration full spectrum root extract. A later sleep trial using KSM-66 standardized to more than 5% withanolides per 300 mg capsule.
• Sensoril is a root and leaf extract. A 2019 trial used it standardized to 21 mg of withanolide glycosides per 60 mg capsule.
• Prolanza is a sustained release root extract standardized to 15 mg of withanolides per 300 mg capsule.
• One study used tablets carrying 500 mg of root extract standardized to 2.5% withanolides, plus 5 mg of piperine.

The ODS conclusion on this point is blunt. Because studies have used various preparations with different extraction and standardization processes and different doses, it's difficult to identify specific extracts or recommended amounts.

So when a label says "clinically studied ashwagandha" without naming which one, the claim isn't attached to anything you can check.

The trial that built the category

The 2012 Chandrasekhar study sits behind almost every cortisol claim on a supplement bottle. It's worth reading in detail rather than as a number on a label.

The design was a single center, prospective, double blind, randomized, placebo controlled trial in India. Sixty-four adults with a history of chronic stress enrolled. Participants took one capsule twice daily for 60 days, and each capsule in the treatment group contained 300 mg of a high concentration full spectrum extract of ashwagandha root, so the daily total was 600 mg. Two kinds of data came out of it: blood serum cortisol, and validated questionnaires covering the Perceived Stress Scale, the General Health Questionnaire-28, and the Depression Anxiety Stress Scale.

At day 60 the treatment group showed a 27.9% reduction from baseline in serum cortisol, against 7.9% in the placebo group. The difference between groups was statistically significant, reported at P = 0.002. Scores on the stress assessment scales had also diverged significantly by day 60.

Adverse events were comparable between groups. Six events in the ashwagandha group and five in placebo, all described as mild. In the ashwagandha group those were nasal congestion, constipation, cough and cold, drowsiness, and decreased appetite. Three subjects were lost to follow up, so adverse event data covered 61 people.

Now the limits, because they get dropped in the retelling.

Sixty-four people. One center. One country. Sixty days. The authors included an investigator affiliated with an Ayurveda health care and research centre, and the trial is the origin point for the extract it tested. A single trial at this size is a strong signal. It isn't a settled result.

What the pooled reviews found

A 2021 systematic review identified seven studies on ashwagandha for stress and anxiety. The total was 491 adults, all from India, with either self reported high stress and anxiety or a diagnosed anxiety disorder, randomized for 6 to 8 weeks. Six used extracts from root alone, from root and leaf, or from unspecified parts. The seventh used dried root powder granules.

Doses ranged from 240 to 1,250 mg per day of extract, or 12,000 mg per day of whole root granules. Overall the studies found that ashwagandha significantly reduced stress and anxiety levels as measured by validated rating scales, reduced sleeplessness and fatigue, and reduced serum cortisol compared with placebo. In several studies the benefits looked greater at 500 to 600 mg per day than at lower doses.

The ODS describes a consistent pattern in later work. It also includes a result that doesn't fit the story, which is the one worth dwelling on.

At two health centers in India, 130 healthy men and women aged 20 to 55 with self reported stress took Prolanza or placebo for 90 days, one 300 mg capsule daily. The ashwagandha group reported improvements in stress levels and sleep quality on validated scales, and had lower serum cortisol.

At the University of Colorado Colorado Springs, 60 students aged 18 to 50 took a root extract containing 2.5 mg withanolides per 350 mg capsule, two capsules daily, or placebo for 30 days. Participants taking ashwagandha were more likely to describe their stress as manageable. Descriptions of the stress itself were comparable between groups.

In Florida, 60 men and women with a mean age of 34 took 225 mg or 400 mg per day of a proprietary root and leaf extract, or placebo, for 30 days. Both ashwagandha groups reported positive effects on stress, anxiety, depression, and food cravings, but only the 225 mg group had lower saliva cortisol than placebo, which isn't the dose-response pattern you'd predict from the label copy. And then there's the result that doesn't fit. A 12 week trial in 120 healthy men and women, mean age 54 to 55, overweight or mildly obese and experiencing low energy and fatigue, tested a root extract providing 200 mg of hydroalcoholic extract standardized to 1.5% withanolides, taken twice daily. Compared with placebo, ashwagandha didn't reduce perceived stress. It did reduce fatigue.

Sit with that one for a second.

A negative result in 120 people is not a rounding error, and it's the trial that label copy leaves out. Effects that show up in one population at one dose don't automatically show up in another.

The sleep evidence

Research here is more limited than the stress literature. It exists, though, and it's worth separating out.

At one center in India, 150 healthy men and women aged 18 to 65 with self reported sleep problems took a root and leaf extract standardized to 21 mg of withanolide glycosides per 60 mg capsule, two capsules daily, or placebo for 6 weeks. Both groups improved on a validated sleep quality scale, but the improvement was larger in the ashwagandha group: 72% versus 29% for placebo. Actigraphy measures moved too, covering sleep efficiency, total sleep time, sleep latency, and waking after sleep onset.

In a second trial, 80 healthy men and women aged 18 to 50, half of them with insomnia, took a root extract standardized to more than 5% withanolides per 300 mg capsule, two capsules daily, or placebo for 8 weeks. Participants with insomnia who took ashwagandha showed improvements in sleep quality, sleep onset latency, mental alertness on rising, and perceived anxiety symptoms. The participants without insomnia reported better sleep but no change in perceived anxiety or alertness on waking.

That split matters. The effect showed up where there was a problem to fix.

A 2021 systematic review and meta-analysis pooled five of these studies. All were conducted in India. A total of 372 adults, either self described as healthy or with insomnia, took ashwagandha or placebo for 6 to 12 weeks, at doses ranging from 250 to 600 mg per day of a root extract or, in one study, 120 mg per day of a root and leaf extract.

The pooled finding was a small but significant effect on improving sleep compared with placebo. The effect was more prominent at 600 mg per day, more prominent when treatment lasted at least 8 weeks, and more prominent in participants with insomnia.

"Small but significant" is the phrase to hold on to. It doesn't mean large.

The safety record

This is the part most product pages leave out. It's also the part the ODS and NCCIH both address.

Liver injury

The NCCIH states that although it's rare, there have been a number of cases linking liver injury to ashwagandha supplements. The ODS cites a case series from Iceland and the US Drug-Induced Liver Injury Network, published in Liver International in 2020, along with later individual case reports.

The ODS adds a qualification that matters: the contents of the products the individuals took weren't independently verified in all cases, and some products were combination products containing ashwagandha and other ingredients.

That cuts both ways, and both directions are worth taking seriously. It means the case reports don't prove ashwagandha was the cause in every instance. It also means the bottles people actually bought were less controlled than the capsules used in the trials.

The NCCIH lists the symptoms to watch for: unusual fatigue, abdominal pain, dark urine, or yellowing of the skin or eyes. Any of those warrants stopping the product and contacting a clinician.

Thyroid

Some research suggests ashwagandha might affect thyroid function. In one study, three adult men who took 500 mg per day of a standardized root and leaf extract for 8 weeks had small increases in blood thyroxine, or T4.

A small trial in 50 participants with subclinical hypothyroidism found that root extract at 300 mg twice daily for 8 weeks lowered serum thyroid stimulating hormone and increased T3 and T4 levels compared with placebo.

Three case reports have described thyrotoxicosis in women taking ashwagandha extract, aged 32 to 73. Dose wasn't specified in two of them. The third involved 1,950 mg per day for more than two months. Discontinuing ashwagandha resolved the symptoms in all three cases.

The NCCIH advises that ashwagandha isn't recommended for people who have autoimmune or thyroid disorders.

Who should not use it

Per the NCCIH and ODS:

• Pregnancy. Ashwagandha should be avoided. Some reports suggest a potential to cause spontaneous abortion.
• Breastfeeding. Shouldn't be used.
• Surgery. Not recommended for people about to have surgery.
• Autoimmune and thyroid disorders. Not recommended.
• Hormone sensitive prostate cancer. Because ashwagandha may increase testosterone levels, the NCCIH advises people with hormone sensitive prostate cancer to avoid it.

Interactions

The NCCIH lists possible interactions with medications for diabetes and high blood pressure, immunosuppressants, sedatives, anticonvulsants, and thyroid hormone medications. The ODS adds antidiabetes medications, antihypertensives, immunosuppressants, and sedatives.

Duration and common effects

The NCCIH states that ashwagandha may be safe when taken short term, up to about 3 months, and that there isn't enough information to reach conclusions about long term safety. In some individuals it may cause drowsiness, stomach upset, diarrhea, and vomiting.

Here's what that means in practice. The most commonly used trial durations were 6 to 12 weeks. The safety data doesn't extend much past 3 months, and most of the marketing assumes indefinite daily use.

What we cannot tell you

We can't tell you which bottle to buy. We don't review branded products, and the trial evidence is tied to specific named extracts at specific standardizations that the average label doesn't disclose.

We can't tell you a dose for a specific condition. The ODS conclusion is that identifying recommended amounts is difficult given the variation in preparations. What we can say is where the trial doses clustered: 500 to 600 mg per day for stress, and 600 mg per day for at least 8 weeks for sleep.

We can't tell you it's safe for you personally. If you take thyroid medication, blood pressure medication, diabetes medication, an immunosuppressant, a sedative, or an anticonvulsant, the interaction list isn't theoretical, and it isn't short.

What this file can do is tell you what was measured, in whom, at what dose, for how long, and what the safety record actually contains.

Frequently asked questions

Does ashwagandha lower cortisol?

One trial found a 27.9% reduction in serum cortisol over 60 days against 7.9% in placebo, in 64 adults taking 600 mg per day of a specific root extract. Later trials have also reported lower cortisol. One 12 week trial in 120 adults found no reduction in perceived stress, so the cortisol finding and the felt experience don't always travel together.

How long does it take to work?

The trials that showed an effect ran 30 to 90 days. The sleep meta-analysis found the effect more prominent when treatment lasted at least 8 weeks. We haven't seen reliable evidence of a same day effect.

What dose was used in the studies?

For stress, the pooled review covered 240 to 1,250 mg per day of extract, with benefits appearing greater at 500 to 600 mg per day. For sleep, the pooled analysis covered 250 to 600 mg per day, with the effect more prominent at 600 mg per day.

Is it safe to take every day indefinitely?

Unknown. The NCCIH states it may be safe short term, up to about 3 months, and that long term safety hasn't been established. Most trials ran 6 to 12 weeks, so the period beyond that is largely unmeasured.

Can it hurt your liver?

Rare cases of liver injury have been linked to ashwagandha supplements. The NCCIH describes them as rare but numerous enough to note. In some reported cases the product contents weren't independently verified, and some products contained other ingredients.

Should I take it if I have a thyroid condition?

The NCCIH doesn't recommend ashwagandha for people with thyroid disorders. Trials have documented increases in T3 and T4 in some participants, and there are three published case reports of thyrotoxicosis.

Does it interact with anything?

The NCCIH lists possible interactions with diabetes medications, blood pressure medications, immunosuppressants, sedatives, anticonvulsants, and thyroid hormone medications.

Is root extract the same as root and leaf extract?

No. The ODS states the chemical composition of root and leaf differ. Results from a root-only extract don't transfer to a root and leaf product, and the reverse is also true.

Does it help with diagnosed anxiety?

The NCCIH states that evidence about effects on anxiety is unclear, while some preparations may be effective for insomnia and stress. Several trials in the pooled review enrolled people with diagnosed anxiety disorders, but the NCCIH's umbrella conclusion is cautious.

Why do some trials show nothing?

Population, dose, extract, and duration all differ. The clearest example is the 12 week trial in 120 overweight or mildly obese adults with fatigue, where ashwagandha reduced fatigue but not perceived stress.

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This article is for general information only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration and are not intended to diagnose, treat, cure, or prevent any disease. Talk with your health care provider before starting any supplement, especially if you take medication or have a health condition.

Sources

• NIH Office of Dietary Supplements, Ashwagandha: Is it helpful for stress, anxiety, or sleep? Fact Sheet for Health Professionals
• NIH Office of Dietary Supplements, Ashwagandha Fact Sheet for Consumers
• NCCIH, Ashwagandha: Usefulness and Safety
• Chandrasekhar K, Kapoor J, Anishetty S. A Prospective, Randomized Double-Blind, Placebo-Controlled Study of Safety and Efficacy of a High-Concentration Full-Spectrum Extract of Ashwagandha Root in Reducing Stress and Anxiety in Adults. Indian J Psychol Med. 2012