Ashwagandha: Benefits, Risks, and What KSM-66 and Sensoril Mean

Ashwagandha has gone from a staple of Ayurvedic medicine to one of the most talked-about supplements for stress and sleep. Its research base is stronger than that of many herbs, but it also comes with genuine safety questions and growing regulatory scrutiny. Here is what the trials show, what extract names like KSM-66, Sensoril and Shoden actually mean, how much people took, and who should avoid it.

What ashwagandha is

Ashwagandha (Withania somnifera) is an evergreen shrub whose root has long been used in Ayurvedic and Unani medicine as an "adaptogen," loosely defined as something that helps the body resist or adapt to stress [1]. It contains steroidal lactones called withanolides, along with alkaloids and many other compounds. Withanolides are thought to drive many of its effects, although preclinical research suggests other components may contribute too [1].

Most commercial supplements use extracts of the root, but some combine root and leaf, and the chemistry of the two plant parts differs [1]. That detail becomes important when you compare products.

KSM-66, Sensoril and Shoden: what the names mean

These are branded extracts made by different ingredient suppliers. They differ in which part of the plant they use, how they are extracted and what compound they are standardized to, which is why their doses look so different.

Because studies have used different preparations, extraction methods and doses, experts caution that it is difficult to single out a best extract or a universal dose [1]. A 2025 regulatory review urged manufacturers to publish their specifications using standard, non-proprietary test methods so products can be compared fairly [16]. The same review found no clear differences so far between root-only and leaf-containing extracts in composition, effects or reported side effects, but said the question deserves more research [16].

Pro tip: A "5% withanolides" root extract and a "35% withanolide glycosides" root-and-leaf extract aren't measuring the same thing. Compare products by the extract used in a trial and the dose in that trial, not by the percentage on the label.

Stress and anxiety: the strongest evidence

Stress is where ashwagandha has the most research. A 2021 systematic review summarized by the NIH found seven trials involving 491 adults, all conducted in India, lasting six to eight weeks. Ashwagandha reduced stress and anxiety scores, sleeplessness, fatigue and blood cortisol compared with placebo, and several studies saw bigger benefits at 500 to 600 mg per day [1].

Individual trials illustrate the pattern:

• KSM-66, 600 mg/day for 60 days. In 64 adults with chronic stress, scores on the Perceived Stress Scale fell 44% with ashwagandha versus 5.5% with placebo, and serum cortisol dropped 27.9% versus 7.9% [2].
• Root extract, 250 or 600 mg/day for 8 weeks. In 60 stressed adults, both doses lowered perceived stress and cortisol, and sleep quality improved compared with placebo [3].
• Shoden, 240 mg/day for 60 days. In 60 adults with high stress, anxiety scores fell significantly compared with placebo, a second questionnaire showed only a trend, and morning cortisol decreased [4].

Pooled analyses agree on direction, if not size. A 2024 meta-analysis of nine trials (558 participants) found average reductions of about 4.7 points on the Perceived Stress Scale and 2.2 points on the Hamilton Anxiety Scale, along with lower cortisol [5]. A 2025 meta-analysis of 14 trials in people with diagnosed mental disorders, mostly anxiety disorders, found improvements in anxiety, stress and sleep quality, while the evidence for depression was less consistent [6]. In 2022, an international psychiatric taskforce provisionally recommended 300 to 600 mg per day of root extract standardized to 5% withanolides for generalized anxiety disorder, while noting that more data are needed [1].

Keep the limitations in view: most trials were small, short and conducted in India [1], and several were funded by, or used products supplied by, the companies that make the extracts [2, 4, 8, 11].

Bottom line on stress: Evidence supports a modest reduction in perceived stress and anxiety over six to eight weeks. Ashwagandha is not a replacement for treatment of an anxiety disorder, so talk to a healthcare professional if anxiety is affecting your daily life.

Sleep

A 2021 meta-analysis of five trials with 400 adults found a small but statistically significant improvement in overall sleep. Benefits were larger in people with diagnosed insomnia, at doses of 600 mg per day or more, and with at least eight weeks of use; no serious side effects were reported [7]. In one included trial, 120 mg per day of Shoden for six weeks improved sleep quality in 72% of participants versus 29% on placebo; in another, 600 mg per day of KSM-66 for eight weeks improved sleep onset and quality in people with insomnia [1].

For chronic insomnia, cognitive behavioral therapy for insomnia remains the recommended first step; our guide to sleep supplements covers how ashwagandha compares with melatonin, magnesium and other options.

Testosterone, strength and exercise

Ashwagandha is heavily marketed to men for testosterone and muscle. The evidence is real but modest:

• In 57 young men starting resistance training, 600 mg per day of KSM-66 for eight weeks produced larger bench-press gains (46.0 kg vs 26.4 kg) and a larger rise in testosterone (96.2 ng/dL vs 18.0 ng/dL) than placebo [8].
• In recreationally active men, 500 mg per day of Sensoril for 12 weeks led to greater gains in squat (19.1 kg vs 10.0 kg) and bench press (12.8 kg vs 8.0 kg) strength than placebo [11].
• In overweight men aged 40 to 70, eight weeks of Shoden increased testosterone 14.7% and DHEA-S 18% more than placebo, but fatigue, vigor and sexual well-being did not differ between groups [9].

A 2026 meta-analysis of 23 trials (1,706 participants) found that ashwagandha lowered cortisol and raised testosterone in men by an average of about 57 ng/dL, with no effect in women [10]. Those are modest average changes, and they are no substitute for proper evaluation and care if you have symptoms of low testosterone. Because ashwagandha may raise testosterone, experts advise that it might not be safe for men with hormone-sensitive prostate cancer [1].

How much to take

Several trials split the dose into two capsules a day [2, 3, 8], while others used a single daily dose [4]. Ashwagandha appears to be well tolerated for up to about three months, but its safety over many months or years is unknown [1]. A sensible approach is a defined trial of 8 to 12 weeks, followed by an honest reassessment rather than indefinite use.

Safety: liver, thyroid, pregnancy and medicines

In clinical trials, side effects have usually been mild and include stomach upset, loose stools, nausea and drowsiness [1]. The more serious concerns are uncommon but important.

Liver injury

Ashwagandha is now a recognized, if rare, cause of liver injury. According to the NIH's LiverTox database, cases typically appear 2 to 12 weeks after starting, with a cholestatic or mixed pattern, jaundice and itching. Most resolve after stopping, but rare deaths or urgent liver transplants have occurred, particularly in people with pre-existing liver disease, and LiverTox advises avoiding ashwagandha in cirrhosis or advanced chronic liver disease [12].

• In five cases from Iceland and the U.S. Drug-Induced Liver Injury Network, all patients developed jaundice; lab analysis confirmed ashwagandha in the available products, and liver tests normalized within one to five months in four patients (one was lost to follow-up) [13].
• In an Indian case series of eight people who took single-ingredient ashwagandha products, five had underlying chronic liver disease; three of them developed acute-on-chronic liver failure and died [14].

Safety note: Stop taking ashwagandha and contact a clinician promptly if you notice yellowing of the skin or eyes, dark urine, itching, nausea, unusual tiredness or abdominal pain. Australia's medicines regulator issued a similar advisory in 2024 [16].

Thyroid

In a trial of 50 adults with subclinical hypothyroidism, 600 mg per day of root extract for eight weeks lowered TSH and raised T3 and T4 compared with placebo [15]. The 2026 meta-analysis found a modest rise in T4 across trials [10], and case reports describe thyrotoxicosis in people taking ashwagandha [1]. If you have a thyroid condition or take thyroid medication, check with your clinician first.

Pregnancy and breastfeeding

Some experts advise against ashwagandha during pregnancy because of reports that it could cause miscarriage. The American Herbal Pharmacopoeia has said its monograph was misrepresented and that there is no evidence the root causes abortion, but reliable safety data in pregnancy are lacking [1]. Since 2020, Australia has required many ashwagandha products to carry a warning that people who are pregnant or considering pregnancy should consult a health professional before use [16]. Avoid ashwagandha if you are pregnant, trying to conceive or breastfeeding.

Medication interactions

Ashwagandha might interact with thyroid hormone, diabetes and blood pressure medicines, immunosuppressants and sedatives [1]. Tell your doctor or pharmacist before combining it with any of these.

Why some countries restrict ashwagandha

Regulators have reached very different conclusions from the same limited evidence. The main actions include:

The authors of a 2025 regulatory review called for a balanced risk-benefit assessment that could lead to stricter rules, such as mandatory warnings, rather than outright bans [16]. Either way, the direction of travel is toward more caution, not less.

How to choose a quality ashwagandha product

• Pick a named, studied extract and match the dose used in trials. Studies have used KSM-66, Sensoril, Shoden and other extracts at very different milligram amounts.
• Check the plant part. Labels should say whether the extract comes from root only or from root and leaf.
• Look for stated standardization (for example, a percentage of withanolides) and independent third-party testing, which is especially important for botanicals that can carry contaminants.
• Avoid proprietary "stress blends" that combine several herbs without disclosing how much ashwagandha each serving contains.
• Be wary of big promises. Claims to "cure anxiety," "boost testosterone like TRT" or "detox" are red flags.
• Plan a time limit. Decide in advance to reassess after 8 to 12 weeks.

Ashwagandha isn't a good fit if you are pregnant or breastfeeding, have liver disease, have a thyroid disorder, have hormone-sensitive prostate cancer, or take sedatives, thyroid, diabetes, blood pressure or immune-suppressing medicines without medical advice [1, 12, 16].

The bottom line

Ashwagandha has reasonable evidence for modestly reducing stress and anxiety and smaller, less certain benefits for sleep, based mostly on short trials of branded extracts, several of them funded or supplied by their makers. It may raise testosterone slightly in men and support strength gains with training. Branded extracts differ in plant part and standardization, so follow the dose used in the trial of the extract you choose, usually 250 to 600 mg per day of root extract or 120 to 240 mg of Shoden. The risks are uncommon but real, especially liver injury and thyroid effects, and several European countries now restrict or discourage its use. If you try it, choose a tested product, limit use to a defined period, and stop immediately if you notice signs of liver trouble.