Ashwagandha

What it is

Ashwagandha is a shrubby plant grown in India and nearby regions. The root (and sometimes leaf) is dried and extracted into capsules, powders and tinctures. It has a long history in Ayurvedic medicine, where it is classed as an adaptogen, a loose term for herbs said to help the body cope with stress.

Most people take it for stress, anxiety, poor sleep or to support gym performance and testosterone. Branded extracts such as KSM-66 (root only) and Sensoril (root and leaf, higher in withanolides) are the ones used in most modern trials, so the research does not automatically apply to any random powder.

It is sold as a food supplement in the UK, but it is not a harmless herb. Regulators in several countries have looked at reports of liver injury, and it can affect thyroid hormone levels.

How it works

The active compounds are thought to be withanolides. They appear to dampen the stress response, including lowering cortisol in some studies, and may act on GABA signalling, which could explain the calming effect. The exact mechanisms in humans are not well pinned down.

What the evidence says

• Moderate Perceived stress and anxiety
  Several small, short randomised trials show modest reductions in self-reported stress, but many are industry-linked and use branded extracts.
• Moderate Sleep quality
  Small improvements in sleep scores are reported, mostly in people with poor sleep or insomnia; the effect is modest.
• Limited Strength and recovery
  A few small trials in trained and untrained men show slightly bigger strength gains than placebo, but the studies are small.
• Limited Testosterone and fertility markers
  Some small studies show modest rises in testosterone or sperm measures, mostly in men with low baseline values; not a replacement for medical care.
• Weak Cognitive function
  Early signs of benefit on attention and memory, but trials are tiny and inconsistent.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Trial doses are commonly 300 to 600 mg of root extract daily, sometimes up to 1,000 mg split across the day. Always follow the label for the specific product.
• Take with food to reduce stomach upset. Some people prefer it in the evening because it can be sedating.
• Many people cycle it (for example 8 to 12 weeks on, a break off) as long-term safety data is thin. There is no formal guideline on this, so treat it as common practice rather than evidence.
• There is no NHS recommended intake or official UK upper limit. Check current guidance from the MHRA and the Food Standards Agency before use.

Forms and what to look for

• KSM-66: root-only extract, standardised to withanolides, used in many trials.
• Sensoril: root and leaf extract, higher withanolide content, so doses are usually lower.
• Plain root powder: cheap but variable in strength, and the trial evidence does not apply to it.
• Look for the extract named on the label, the withanolide percentage and the per-capsule dose. Avoid proprietary blends that hide amounts.

What to expect, and when

• Do not expect an effect in days. Trial benefits generally appear after 4 to 8 weeks of daily use.
• Some people feel calmer or sleepier within a couple of weeks; many feel nothing noticeable.
• If there is no change after 8 to 12 weeks, it is probably not doing much for you.

Side effects

• Drowsiness, stomach upset, nausea or loose stools are the most common complaints.
• Headache or dizziness in some people.
• Rarely, liver injury: yellow skin or eyes, dark urine, pale stools, itching or persistent tiredness should prompt stopping and urgent medical advice.
• Can raise thyroid hormone levels (T3 and T4), which may cause jitteriness, palpitations or heat intolerance.
• Some people report emotional blunting or low mood on it, though this is anecdotal.

Interactions

• Thyroid medication (levothyroxine or antithyroid drugs): can change thyroid hormone levels, so a clinician should know.
• Sedatives, sleeping tablets and benzodiazepines: additive drowsiness is possible.
• Immunosuppressants: ashwagandha may stimulate immune activity, which could work against them.
• Blood pressure and diabetes medicines: may add to their effect, so monitoring matters.
• Alcohol and other liver-stressing drugs or supplements: best avoided given liver injury reports.

Who should avoid it

• Anyone pregnant or trying to conceive; traditional use and animal data suggest possible risk.
• Breastfeeding.
• People with existing liver disease or a history of liver problems.
• People with thyroid conditions, unless supervised by a clinician.
• Those with autoimmune conditions or taking immunosuppressants.
• Anyone due for surgery in the next couple of weeks, because of possible sedative interactions.

Risks and safety

• Rare but serious cases of liver injury have been reported, and some regulators have issued warnings. Risk seems low but is real and not predictable.
• Supplement quality is variable, and contamination with heavy metals has been found in some Ayurvedic products.
• Ashwagandha is not on the WADA prohibited list as a named substance, but athletes should still choose batch-tested products to avoid contaminants.

Buying well: quality and testing

• Choose products stating the extract (such as KSM-66 or Sensoril) and the withanolide percentage.
• Look for third-party testing for contaminants and heavy metals (for example NSF, Informed Sport or an independent lab certificate).
• Be wary of huge claims of mg per capsule that refer to raw powder rather than extract.
• Avoid proprietary blends and products making disease claims.

Bottom line

Ashwagandha has more human trial support than most herbs for stress and sleep, with modest effects. It suits someone who wants to try a short, supervised course with a quality extract. Because of rare liver injury reports and thyroid effects, it is worth speaking to a pharmacist or GP first if you take any medication or have any thyroid or liver issue, and stopping at the first sign of jaundice or unusual tiredness.