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Does ashwagandha work for stress? Why your biology has the final say

Small clinical trials suggest ashwagandha, a herb used in Ayurvedic medicine for centuries, can lower perceived stress and cortisol over six to eight weeks. But most studies are small and short; it isn't safe for everyone, and people respond to it differently. Part of that difference may come down to your gut.

October is Mental Health Awareness Month in South Africa, and it overlaps with National Nutrition Week. It's a good time to look at a herb that keeps turning up in wellness conversations, and to ask a better question than "does it work?". The better question is "would it work for me?"

What is ashwagandha?

Ashwagandha (Withania somnifera) is a shrub in the nightshade family, the same family as tomatoes, potatoes and peppers. Its root has been used in Ayurvedic practice for centuries. Today it's often called an adaptogen, a loose term for plants thought to help the body cope with stress.

What does the research say about stress, anxiety and sleep?

The evidence is promising but limited. A 2021 review pooled seven trials with 491 adults. Compared with placebo, ashwagandha reduced self-rated stress, anxiety, poor sleep, fatigue and cortisol levels over six to eight weeks.

For sleep, a 2021 analysis of five studies with 372 adults found a small benefit, mostly in people with insomnia.

There are caveats. All seven stress trials were run in India, most were small, and they used different extracts and amounts. One 12-week trial found no drop in perceived stress at all. Researchers still describe the evidence as early.

Is ashwagandha safe?

For most healthy adults, short-term use of up to about three months seems well tolerated. Long-term safety hasn't been studied. Reported effects include:

•      Stomach upset, loose stools, nausea and drowsiness

•      Liver injury, reported in rare case reports, which usually cleared up after stopping

•      Thyroid changes, as ashwagandha can raise thyroid hormone levels

•      Medicine interactions with thyroid, diabetes, blood pressure, immune-suppressing and sedative medicines

Denmark banned ashwagandha in 2023. In 2024 France's food safety agency advised certain groups not to use it, including pregnant and breastfeeding women.

Who should avoid ashwagandha?

Speak to your doctor or pharmacist first, or avoid it altogether, if you:

•      Are pregnant, trying to conceive or breastfeeding

•      Have a thyroid condition or take thyroid medicine

•      Have liver problems

•      Have a hormone-sensitive condition such as prostate cancer

•      Take medicine for diabetes, blood pressure or sleep, or immunosuppressants

•      React to nightshades

Why doesn't ashwagandha work the same for everyone?

This is where your gut comes in. Trillions of microbes in your gut break down the plant compounds you eat. Researchers think the effect of many herbs depends on how gut bacteria transform their compounds into forms the body can absorb.

Because everyone's gut microbiome is different, two people can take the same herb and get different results. Scientists still need human trials to confirm how much this explains, but it's one reason a one-size-fits-all approach to stress falls short.

What else helps with stress?

Before reaching for any herb, the basics carry the most evidence:

•      Move most days. Even a 20-minute walk lowers stress hormones.

•      Protect your sleep. Aim for a regular bedtime, even over weekends.

•      Eat for your gut. Fibre from foods like beans, lentils, oats and vegetables feeds the microbes that produce calming compounds.

•      Talk to someone. If stress or anxiety is affecting your daily life, the SADAG helpline is free and available every day.

How can you find out what your body needs?

The Viome gut microbiome test uses RNA sequencing to look at what your gut microbes are doing, not just which ones are there. Your results show how your biology may be handling areas like stress and inflammation, along with food recommendations matched to you.

It won't diagnose anything, but it gives you and your healthcare provider a clearer starting point than guesswork.

Next Biosciences brings Viome to South Africa. Get the Viome test from Next Biosciences

 

FAQ

1. How long does ashwagandha take to work? Most trials measured effects after six to eight weeks. Some sleep studies saw benefits after eight weeks or more.

2. Can ashwagandha affect your thyroid? Yes. Studies show it can raise thyroid hormone levels. People with thyroid conditions or on thyroid medicine should speak to their doctor first.

3. Is ashwagandha safe in pregnancy? No. Health authorities in Denmark and France advise against it, and pregnant or breastfeeding women should avoid it.

4. Why does ashwagandha work for some people and not others? Extracts and doses differ, and gut bacteria may change how your body processes plant compounds. Everyone's microbiome is different.

 

Sources

•      Ashwagandha fact sheet for health professionals, NIH Office of Dietary Supplements, updated May 2025

•      Intestinal microbiota-associated metabolites: crucial factors in the effectiveness of herbal medicines and diet therapies, Wang et al., Frontiers in Physiology, 2019