Ashwagandha has better human evidence for stress than almost any other adaptogen, and the headline number comes from a single well-known trial: 64 chronically stressed adults taking 300 mg of a standardised root extract twice daily for 60 days showed a 27.9% reduction in serum cortisol, versus 7.9% in the placebo group (Chandrasekhar et al., Indian Journal of Psychological Medicine, 2012). Stress-scale scores fell significantly too.
That is a genuinely strong result. It is also one single-centre study of 64 people, and it is quoted on roughly every ashwagandha label in existence. Here is the fuller picture: what the herb is, what the wider evidence base looks like, what dose and form matter, and the safety issue that has become more prominent in recent years.
What ashwagandha is
Withania somnifera — ashwagandha, Indian winter cherry, or ashvagandha in Sanskrit — is a small shrub in the nightshade family. It has been used in Ayurveda for well over two thousand years, classified as a rasayana: a rejuvenative tonic taken over time rather than a remedy taken for an acute complaint.
The name is worth knowing. Ashva means horse and gandha means smell — the fresh root has a distinctly horsey odour. The traditional gloss is that it confers the strength and vitality of a horse.
The compounds of interest are withanolides, a family of steroidal lactones concentrated in the root. Standardised extracts are typically specified by withanolide percentage — commonly 2.5% or 5%.
What "adaptogen" means and does not mean
An adaptogen is defined as a substance that helps the body resist non-specific stressors and return toward homeostasis. It is a useful framing and a slippery one — "helps you handle stress" resists precise measurement in a way that "lowers blood pressure by 6 mmHg" does not. The value of the ashwagandha literature is that it has largely moved past the vague framing to measure specific things: serum cortisol, validated stress scales, sleep quality indices.
The evidence, in order of strength
Cortisol and perceived stress
This is the best-supported claim. The 2012 Chandrasekhar trial is the most cited: randomised, double-blind, placebo-controlled, 64 adults with a history of chronic stress, 300 mg of a high-concentration full-spectrum root extract twice daily for 60 days. Serum cortisol dropped 27.9% in the treatment group against 7.9% in placebo, with a strong statistical result (P = 0.0006). Scores fell significantly across all the stress-assessment scales used. Adverse effects were mild and comparable between groups.
Several later randomised trials have found effects in the same direction on perceived stress and anxiety scores, and systematic reviews have generally concluded there is a consistent signal — while noting the studies are small, often industry-funded, and heterogeneous in the extracts and doses used.
The fair summary: the direction of effect is consistent and the mechanism is plausible, but the evidence base is built from many small trials rather than a few large ones.
Sleep
Reasonably supported. Multiple trials report improvements in sleep onset latency and sleep quality, particularly in people with insomnia. The species name — somnifera, sleep-inducing — reflects a traditional use that modern data has partly corroborated.
Everything else
Claims around strength and muscle gain, testosterone, cognition, and thyroid function have some small trials behind them but nothing approaching the consistency of the stress and sleep data. Treat them as preliminary.
Dose, form, and timing
Dose
Trials showing benefit have mostly used 300–600 mg per day of a root extract standardised to withanolide content, usually split into two doses. Below about 250 mg per day of a standardised extract, you are into territory the research does not really cover.
Note the distinction between extract and raw root powder. Traditional Ayurvedic preparations use whole root powder at much higher gram-scale doses. A 300 mg dose of raw powder is not equivalent to 300 mg of a standardised extract, and product labels are frequently unclear about which they contain.
Root versus leaf
Traditional use and the great majority of clinical trials use the root. Some cheaper products use leaf material or aerial parts, which have a different withanolide profile and are not what was studied. Look for "root extract" explicitly.
Timing
Ashwagandha is a slow-acting herb. Trials run 8 to 12 weeks; people rarely report much in the first fortnight. This is unlike ginger or caffeine, where the effect is same-day — a distinction we work through in our guide to the best time to take wellness shots by ingredient.
Many people take it in the evening, on the logic that the sleep benefit is best captured overnight and that lowering cortisol in the evening aligns with the natural circadian curve. Others split it morning and evening as the trials did. There is no strong evidence favouring either. If you are thinking about how to sequence functional ingredients through the day, our guide to Ayurvedic morning routine drinks works through the same question for the morning half of the routine.
Taking it with fat
Withanolides are fat-soluble. Traditional preparations pair ashwagandha with warm milk and ghee — the classic ashwagandha ksheerapaka. There is reasonable pharmacological logic to taking it with a fat source rather than water alone.
The safety issue you should know about
Ashwagandha is generally well tolerated in trials, with mild and placebo-comparable adverse effects. Common complaints are gastrointestinal upset and drowsiness.
However, over the past several years there have been accumulating case reports of liver injury associated with ashwagandha supplements. Some national regulators — Denmark's food authority among the earliest — have restricted or warned about ashwagandha products, and several countries now require liver warnings. The cases are rare relative to how widely the herb is used, and causality is often difficult to establish given the general quality problems in the supplement market. But the signal is real enough that it should inform how you use it.
Practical implications: use it in courses rather than indefinitely, buy from suppliers who publish third-party testing, and stop immediately and see a doctor if you develop jaundice, dark urine, persistent nausea, or right-upper-abdominal pain.
Who should not take ashwagandha
- Pregnancy. Traditionally regarded as abortifacient at higher doses. Avoid.
- Breastfeeding. Insufficient data.
- Autoimmune conditions (lupus, rheumatoid arthritis, Hashimoto's) — ashwagandha appears to stimulate some immune activity.
- Thyroid disease or thyroid medication. It can raise thyroid hormone levels; combining with levothyroxine risks pushing you hyperthyroid.
- Existing liver disease or other hepatotoxic medications.
- Sedatives and benzodiazepines — additive drowsiness.
- Nightshade sensitivity — it is a solanaceous plant.
- Before surgery — stop two weeks prior due to sedative effects.
How to think about it honestly
Ashwagandha sits in an unusual place: it is a traditional botanical with unusually decent modern trial data, and it is simultaneously the subject of some of the most aggressive supplement marketing on the market. Both things are true.
If you have chronic, grinding, low-grade stress and you want to try something with a plausible mechanism and real randomised evidence behind it, ashwagandha is a defensible choice — 300–600 mg daily of a standardised root extract, taken in a 8–12 week course, from a supplier that tests its material.
What it is not is a substitute for addressing the source of the stress, and it is not something to take forever without thought. The traditional framing had this right: a rasayana was taken in courses, within a broader routine of sleep, food, and daily rhythm. The herb was never meant to be the whole intervention.
This article is general information, not medical advice. Ashwagandha interacts with several classes of medication. Speak to a clinician before starting it, especially if you take thyroid, sedative, or immunosuppressant medication.
Frequently asked questions
How long does ashwagandha take to work for stress?
Most clinical trials run 8 to 12 weeks, and the 2012 cortisol study measured its result at 60 days. Some people notice changes in sleep within one to two weeks, but the stress and cortisol effects appear to build over a longer period. If you have taken it for four weeks and felt nothing, that is not unusual — but it is also worth reassessing whether the product is a standardised root extract at a studied dose.
What dose of ashwagandha should I take?
Trials showing benefit generally used 300 to 600 mg per day of a root extract standardised to withanolide content, often split into two doses. Be careful comparing products: 300 mg of standardised extract is very different from 300 mg of raw root powder, and many labels do not make the distinction clear. Look specifically for "root extract" with a stated withanolide percentage.
Is it safe to take ashwagandha every day long term?
Most trials ran 8 to 12 weeks, so long-term daily use is not well studied. There have also been case reports of liver injury associated with ashwagandha supplements, which led several regulators to issue warnings. A cautious approach is to take it in defined courses rather than indefinitely, buy third-party-tested products, and stop and seek medical advice if you develop jaundice, dark urine, or persistent nausea.
Should I take ashwagandha in the morning or at night?
There is no strong evidence favouring either. The original trials split the dose morning and evening. Many people prefer the evening because ashwagandha has sedative properties and a sleep benefit, and because lowering cortisol at night aligns with the body's natural rhythm. If it makes you drowsy during the day, move it to the evening.
Can I take ashwagandha with thyroid medication?
Not without medical supervision. Ashwagandha has been shown to raise thyroid hormone levels, so combining it with levothyroxine or another thyroid medication risks pushing you into hyperthyroidism. This is one of the clearest interaction concerns with the herb, and it applies whether your thyroid condition is treated or subclinical.