Ashwagandha

This is the reason most people buy ashwagandha, and it's where the human evidence is genuinely strongest - so it's worth walking through what the studies actually did.

The famous one is Chandrasekhar and colleagues, published in the Indian Journal of Psychological Medicine in 2012. The researchers recruited 64 adults with a history of chronic stress and split them into two groups. One group took 300 mg of a concentrated full-spectrum root extract twice a day; the other took identical dummy capsules. Neither the participants nor the researchers handing out the capsules knew who got which - that's what 'double-blind' means, and it's how you stop hope from doing the work. After 60 days, the ashwagandha group scored significantly lower on every stress questionnaire used. More interestingly, they also measured a physical marker: serum cortisol, the body's main stress hormone. It fell about 28 percent in the ashwagandha group compared with about 8 percent on placebo. A subjective feeling and an objective blood measurement moving together is a meaningfully stronger result than either alone.

It is not one study standing alone, which is unusual for a botanical. A 2021 systematic review pulled together seven randomised trials covering 491 adults, using doses from 240 to 1,250 mg a day of extract over 6 to 8 weeks. Across them, ashwagandha significantly reduced stress and anxiety on validated rating scales, reduced sleeplessness and fatigue, and lowered serum cortisol versus placebo - with benefit appearing clearer at 500 to 600 mg a day than at lower doses. Trials published since have mostly pointed the same way, including a 90-day study of 130 stressed adults in India using a sustained-release extract, and a 30-day trial of 60 adults in Florida using a root-and-leaf extract, where the lower 225 mg dose also produced lower salivary cortisol.

The honest limitations. Every participant in that seven-trial review was recruited in India; so was everyone in most of what followed. The trials are small and short - two months is typical, and none tell you anything about a year of use. Many were conducted with a branded extract supplied by its manufacturer, and industry-funded supplement trials tend on average to report rosier results. And the effects, while statistically real, are modest: this is 'the week felt more manageable', not 'my stress disappeared'. One 2023 Australian trial in 120 tired, overweight adults found no reduction in perceived stress at all - it improved fatigue instead. Consistent direction, unimpressive size, imperfect evidence.

The botanical name is a hint: somnifera is Latin for 'sleep-bringing'. The modern evidence is smaller than the stress evidence but points the same way, with one important nuance - it helps people who sleep badly far more than people who already sleep well.

The clearest single trial is Deshpande and colleagues, published in Sleep Medicine in 2020. They enrolled 150 adults aged 18 to 65 in India who reported poor, unrefreshing sleep, and randomised them to a root-and-leaf extract (Shoden, 120 mg a day standardised to withanolide glycosides) or placebo for six weeks. What makes this study better than most is that it didn't rely only on people's opinions: participants wore wrist actigraphy monitors, which measure movement and estimate sleep objectively. Self-reported sleep quality improved in both groups - placebo included, which tells you something about expectation - but improved considerably more on ashwagandha (72 percent versus 29 percent). The actigraphy backed it up, showing better sleep efficiency, longer total sleep, shorter time to fall asleep and less waking during the night.

A second trial by Langade and colleagues took 80 adults, half with diagnosed insomnia and half without, and gave them 600 mg a day of a root extract (KSM-66) or placebo for eight weeks. The people with insomnia improved on sleep quality, time to fall asleep, morning alertness and anxiety. The people without insomnia reported slightly better sleep but no change in anxiety or morning alertness. If your sleep is already fine, there may not be much room to improve it.

Pulling it together, Cheah and colleagues published a systematic review and meta-analysis in PLOS ONE in 2021, combining five randomised trials and 400 participants. Their conclusion was carefully worded: a small but statistically significant effect on overall sleep, more prominent in people diagnosed with insomnia, at doses of 600 mg a day or more, and over treatment periods of at least eight weeks.

The limitations again matter. All five trials in the meta-analysis were conducted in India. There was substantial variation between studies. 'Small but significant' means measurable, not dramatic - nobody should expect a sleeping-pill effect. And the reviewers themselves noted that safety data for long-term use simply isn't there.

Stress and anxiety get lumped together in supplement marketing, but they aren't the same thing, and the evidence for them isn't the same strength either. Everyday stress is a feeling. Clinical anxiety is a diagnosis. Ashwagandha's data on the first is better than its data on the second.

What exists is encouraging but thin. Several small randomised trials have measured anxiety alongside stress and found improvements on validated rating scales - the 2021 systematic review of seven trials in 491 Indian adults reported reduced anxiety as well as reduced stress. A trial of 54 adults with mild-to-moderate stress and anxiety in India, using a 500 mg standardised root extract with piperine, found significantly lower anxiety scores at day 60 than placebo. A small Iranian trial in people with diagnosed generalised anxiety disorder reported benefit too.

The most useful summary comes from an international expert taskforce convened by the World Federation of Societies of Biological Psychiatry and the Canadian Network for Mood and Anxiety Treatments. In their 2022 clinician guidelines on nutraceuticals in psychiatry, they gave ashwagandha a provisional recommendation for generalised anxiety disorder at 300 to 600 mg a day of root extract standardised to 5 percent withanolides - and explicitly stated they could not offer a stronger recommendation without more data. That is a genuinely fair reading: enough signal for a cautious professional to consider it, nowhere near enough to call it established.

NCCIH, the NIH's complementary health centre, is blunter still. Their assessment is that some ashwagandha preparations may be effective for insomnia and stress, but that the evidence on anxiety specifically is unclear.

The practical takeaway: if you have an anxiety disorder, this is a conversation to have with your doctor, not a self-treatment decision - particularly because ashwagandha may interact with sedatives and other psychiatric medication. Nothing on this page is a substitute for proper care.

This is where the internet gets loudest and the evidence gets thinner - so it's worth being precise about what was measured.

The study everyone cites is Wankhede and colleagues, 2015. They recruited 57 healthy men aged 18 to 50 with little previous resistance-training experience, and randomised them to 300 mg of root extract twice daily or a starch placebo. Both groups then followed the same eight-week resistance-training programme. At the end, the ashwagandha group had gained more bench-press and leg-extension strength, more arm and chest circumference, and showed a larger rise in testosterone and a larger fall in exercise-induced muscle damage markers than placebo.

Read that carefully, because the framing matters. These were untrained men starting a structured lifting programme - a group who will gain strength regardless. The finding is that ashwagandha appeared to improve the response to training, not that it built muscle on its own. And the testosterone change, while statistically significant, started from normal levels in healthy young men; it is not comparable to what a medical testosterone intervention does. A 2021 systematic review of herbs and testosterone concluded that ashwagandha was among the few with any supportive human data, while noting the studies were small and heterogeneous.

NCCIH's own summary is the sober one: there is some limited evidence that taking ashwagandha for two to four months may increase testosterone levels and sperm quality, and there isn't enough evidence to say whether it helps athletic performance. Those two sentences sit side by side in the same fact sheet, which tells you how narrow the finding really is.

One consequence you won't see on a pre-workout label: because ashwagandha may raise testosterone, expert bodies including NCCIH advise that men with hormone-sensitive prostate cancer should avoid it. A hormonal effect large enough to be worth advertising is large enough to be worth a warning.

This one is on the page as a safety issue rather than a benefit, because that's the honest way to present it - even though plenty of websites sell it as a thyroid remedy.

The key study is Sharma, Basu and Singh, published in the Journal of Alternative and Complementary Medicine in 2018. Fifty people with subclinical hypothyroidism - meaning raised TSH with thyroid hormones still in the low-normal range - were randomised to 300 mg of ashwagandha root extract twice daily or placebo for eight weeks. Blood tests at the end showed significantly lower TSH and significantly higher T3 and T4 in the ashwagandha group compared with placebo. In thyroid terms, that's the herb pushing hormone levels upward.

Supplement marketing reads that as 'supports thyroid function'. A more careful reading is that ashwagandha has real, measurable hormonal activity - and anything that can raise thyroid hormones in someone with an underactive thyroid can also push someone else too far. That isn't hypothetical. An earlier study found small increases in T4 in men taking a root-and-leaf extract for eight weeks, in a trial that wasn't even about the thyroid. And there are at least three published case reports of thyrotoxicosis - an overactive thyroid state - in women taking ashwagandha, including a 32-year-old who developed weight loss, shakiness and palpitations six weeks after starting and shortly after increasing her dose. Her symptoms and blood tests returned to normal after she stopped.

Why the grade is 'Preliminary': one small 50-person trial, one incidental finding and a handful of case reports is not a body of evidence. It is enough to establish that an interaction is plausible and worth taking seriously - not enough to characterise it properly, predict who it happens to, or recommend ashwagandha for any thyroid purpose.

The practical rule is simple. If you have hypothyroidism, hyperthyroidism, Hashimoto's, or you take levothyroxine or any other thyroid medication, do not start ashwagandha without talking to the clinician who manages it. NCCIH lists thyroid disorders among the conditions for which ashwagandha is not recommended, and lists thyroid hormone medication among the drugs it may interact with.

Long before anyone measured a cortisol level, ashwagandha had a settled place in Ayurveda - and in Canada, that traditional record is actually the legal basis for most of what a product may say.

In the Ayurvedic system it is classified as a rasayana: a rejuvenating tonic, given not to treat a specific complaint but to rebuild strength and vitality, particularly in old age or during recovery from illness. It is also described as a nervine that balances aggravated Vata - the elemental principle associated in Ayurveda with movement, dryness and, when disturbed, restlessness and anxiety. The name itself carries the intent. Ashwa-gandha means 'smell of horse', a reference both to the root's distinctly musky odour and to the strength of a stallion it was said to impart.

Health Canada's Natural and Non-prescription Health Products Directorate publishes a compendial monograph for Withania somnifera root, most recently dated February 2025. It permits exactly these traditional statements, sourced to Ayurvedic pharmacopoeias and classical texts: traditionally used in Ayurveda as a rasayana (rejuvenative tonic); to relieve general debility, especially during convalescence or old age; to help relieve restlessness and/or nervousness (which helps to promote sleep); to balance aggravated Vata (nervine); and for memory enhancement. Separately, it permits one non-traditional statement drawn from Western herbal practice: used in Herbal Medicine as an adaptogen to help increase energy and resistance to stress over time.

The dose ceilings are set by the claim. For the traditional Ayurvedic uses, 2 to 6 grams of dried root per day for dry, powdered and non-standardised preparations. For the adaptogen claim, 2.5 to 6.5 grams of dried root or whole plant per day. Concentrated standardised extracts - the kind used in nearly all the clinical trials - are dosed far lower and expressed as their dried-root equivalent, which is why a 600 mg capsule can sit legitimately inside a 6 gram limit.

What traditional use is, and isn't: it is a genuine, documented record of how a plant has been used by a coherent medical system over a long time. It is not clinical proof of effect. Health Canada is explicit that these are traditional-use statements, and that's exactly how we present them.