Ashwagandha: What the Evidence Says and Who Should Be Cautious

What is ashwagandha and how is it used?

Ashwagandha (Withania somnifera) is a shrub used for centuries in Ayurvedic traditional medicine. Modern supplements typically use standardised root or root-and-leaf extracts, often described by their withanolide content, and are commonly promoted as an "adaptogen" said to help the body manage stress.

Because it is sold as a dietary supplement rather than a registered medicine in New Zealand, it has not gone through the same approval process as prescription or pharmacy medicines, and manufacturers are limited to general wellbeing claims rather than claims to treat or cure a specific illness.

What does the stress and sleep research show?

Several systematic reviews and meta-analyses of randomised controlled trials report that standardised ashwagandha extracts, generally taken for six to eight weeks or longer, are associated with reductions in perceived stress, anxiety scores and cortisol compared with placebo. A number of smaller trials also report improvements in sleep quality and time to fall asleep.

This is a genuinely more substantial evidence base than many other adaptogens, but it is still an emerging area. Trials differ in extract type, dose, duration and the population studied, which is why results are described as promising rather than conclusive. It is reasonable to view ashwagandha as one option to discuss rather than an established, guaranteed solution.

Who should be cautious or avoid ashwagandha?

Ashwagandha is not recommended during pregnancy and should not be used while breastfeeding, because there is not enough reliable human safety data to support its use in these situations. People with autoimmune conditions, thyroid disorders or hormone-sensitive prostate cancer should also avoid it or seek medical advice first, since ashwagandha may influence thyroid hormone levels and testosterone.

It may interact with medicines for diabetes, high blood pressure, thyroid conditions, sedatives, anti-seizure medication and immunosuppressants. Although rare, cases of liver injury linked to ashwagandha supplements have been reported, and long-term safety beyond a few months of use has not been well studied.

• Avoid during pregnancy and breastfeeding.
• Speak with a doctor first if you have a thyroid or autoimmune condition.
• Check for interactions if you take diabetes, blood pressure, thyroid, sedative or anti-seizure medication.
• Use short term (research is mostly limited to around three months) unless advised otherwise by a health professional.