Ashwagandha has become one of the most widely studied herbal supplements in the world, and the evidence base for its effects on stress and anxiety is among the strongest of any single herb. It is not a sedative and does not work in the same way as pharmaceutical anxiolytics — it works by modulating the body’s stress response system over time. This article covers what ashwagandha is, what the research shows, how to use it, and what to be aware of before starting.
What Is Ashwagandha?
Ashwagandha (Withania somnifera) is a small shrub native to India, North Africa, and the Mediterranean. Its roots and leaves have been used in Ayurvedic medicine for at least 3,000 years, primarily as a rasayana — a rejuvenating tonic for energy, vitality, and resistance to disease. In modern terms, it is classified as an adaptogen: a herb that helps the body adapt to physiological and psychological stress by supporting the stress response system rather than suppressing it. The primary active compounds are withanolides, a class of steroidal lactones found predominantly in the root.
What the Research Shows
Ashwagandha has been evaluated in multiple randomised, double-blind, placebo-controlled trials for stress and anxiety — a level of evidence that is rare for herbal supplements. A 2024 meta-analysis published in BJPsych Open, which searched PubMed, Cochrane, Scopus, and Web of Science through September 2024, identified multiple eligible RCTs and found statistically significant reductions in Perceived Stress Scale scores, Hamilton Anxiety Scale scores, and serum cortisol levels compared to placebo.
An earlier meta-analysis (Arumugam et al., Explore, 2024) covering nine RCTs with 558 participants found significant improvements in perceived stress (mean difference −4.72 on the PSS), anxiety (mean difference −2.19 on the Hamilton scale), and serum cortisol (mean difference −2.58). Doses in included trials ranged from 125 to 600 mg daily for 30 to 90 days.
Key individual trials include:
- A 60-day RCT (Chandrasekhar et al., 2012, PMC) in 64 adults with chronic stress found significant reductions in all stress-assessment scores and a substantial reduction in serum cortisol in the ashwagandha group versus placebo (p=0.0006). No serious adverse events occurred.
- A 60-day RCT (Lopresti et al., 2019, PubMed) in stressed healthy adults using 240 mg daily found statistically significant reductions on the Hamilton Anxiety Rating Scale and meaningfully lower morning cortisol compared to placebo.
- A 2023 RCT (Majeed et al., Medicine) using 500 mg of standardised ashwagandha root extract found significant improvements in perceived stress, generalised anxiety disorder scores, and quality of life, along with reductions in morning salivary cortisol and increases in urinary serotonin.
The overall picture from the clinical trial literature is consistent: ashwagandha significantly reduces self-reported stress and anxiety scores and measurably lowers cortisol in people under stress, at doses between 240–600 mg daily over 4–12 weeks.
How Ashwagandha Works on Stress and Anxiety
Ashwagandha’s anti-stress effects appear to operate primarily through modulation of the hypothalamic-pituitary-adrenal (HPA) axis — the body’s central stress response system. Under chronic stress, the HPA axis drives sustained high cortisol output, which disrupts sleep, increases anxiety, impairs cognitive function, and suppresses immune activity. Withanolides appear to help regulate this axis, reducing the chronic over-activation that characterises stress-related conditions.
Additionally, ashwagandha has demonstrated GABA-mimetic activity in some research, meaning it may interact with the same inhibitory neurotransmitter pathway targeted by benzodiazepines — but at a much weaker level and without the same risk of dependence or sedation. It also appears to support serotonin levels, as shown in the 2023 Majeed trial, which may contribute to its mood-stabilising effects.
Importantly, ashwagandha is not a fast-acting remedy. Unlike passionflower or valerian, which have more immediate calming effects, ashwagandha’s stress-reduction benefits typically become noticeable after 4–8 weeks of consistent daily use. It works by gradually rebalancing the stress response system, not by suppressing it acutely.
How to Take Ashwagandha
Dose
The most consistently effective doses in clinical trials range from 300 to 600 mg of standardised root extract daily. Most trials used 240–600 mg taken once or twice daily. Products should ideally be standardised for withanolide content (commonly 2.5–5%). Unstandardised root powder at 1,000–5,000 mg can also be effective but requires higher amounts to deliver equivalent withanolide levels.
Timing
Taking ashwagandha at night is common and supported by evidence — several trials administered it in the evening, and it may support sleep quality as a secondary benefit. Morning use is also effective for daytime stress management. Taking it with food reduces the risk of mild gastrointestinal upset, which is the most common side effect at higher doses.
Duration
A minimum trial of 4–8 weeks is needed to assess effectiveness. Most trials ran for 60 days. There are no established guidelines on maximum duration of use; many people use it cyclically (8–12 weeks on, then a break) as a precautionary measure, though there is no strong evidence that continuous use at standard doses is harmful in healthy adults.
Safety and Important Cautions
Thyroid: Ashwagandha may increase thyroid hormone levels. People with hyperthyroidism or those taking thyroid medication (levothyroxine) should consult their doctor before use, as it could potentiate thyroid activity.
Pregnancy: Not recommended. Some historical sources suggest potential uterotonic activity, and the precautionary recommendation across European and international health agencies is to avoid use during pregnancy. Denmark banned ashwagandha supplements in 2023 partly over this concern; the French ANSES agency recommended against use in pregnant and breastfeeding women in 2024.
Autoimmune conditions: Ashwagandha has immunomodulatory activity. People with autoimmune conditions (rheumatoid arthritis, lupus, Hashimoto’s) or those taking immunosuppressive medications should consult their doctor before use.
Liver: Rare cases of hepatotoxicity have been reported with ashwagandha supplements, most in the context of very high doses or adulterated products. At standard supplemental doses in healthy adults, liver injury is uncommon, but people with pre-existing liver conditions should be cautious.
Sedative medications: Ashwagandha has mild sedative properties and may enhance the effect of benzodiazepines, sleep medications, or other CNS depressants. Avoid combining without medical guidance.
Common mild side effects: At standard doses, some people report mild gastrointestinal discomfort (particularly on an empty stomach), drowsiness, or headache when starting. These typically resolve within the first week or two.
Ashwagandha vs Other Herbs for Stress and Anxiety
Ashwagandha is best suited for chronic, background stress — the persistent low-to-moderate anxiety that builds up over weeks and months. It is not appropriate as an acute anxiolytic for panic attacks or situational anxiety. For acute anxiety, passionflower or lemon balm produce more immediate effects. For anxiety that significantly disrupts daily functioning, ashwagandha is a reasonable adjunct but is not a substitute for professional assessment and treatment.
Compared to rhodiola rosea — the other major adaptogen with strong clinical evidence — ashwagandha tends to produce a more calming, grounding effect and is better suited to anxiety-predominant stress. Rhodiola is typically better suited to fatigue, low motivation, and burnout-type presentations. The comparison is explored in more depth in the article on ashwagandha vs rhodiola for stress.
Summary
- Ashwagandha has the strongest clinical evidence of any herb for reducing chronic stress and anxiety, with multiple RCTs and meta-analyses confirming statistically significant effects on validated stress scales and cortisol levels.
- It works by modulating the HPA axis and lowering chronic cortisol over-activation — not by suppressing the nervous system acutely.
- Effective dose: 300–600 mg of standardised root extract daily for at least 4–8 weeks. Take with food to minimise GI effects.
- Best suited to chronic background stress and generalised anxiety; not appropriate for acute anxiety episodes.
- Avoid during pregnancy, with thyroid medication, and with immunosuppressants. Rare hepatotoxicity cases have been reported at high doses.