Ashwagandha is one of the most widely studied herbal supplements in the world — and for most healthy adults it is very well tolerated. But like any supplement, it's worth knowing what to expect before you start.

Here's an honest, straightforward guide to the side effects, who should avoid ashwagandha, and how to get the most out of it safely. 

Is Ashwagandha Safe?

For most healthy adults, yes. Multiple clinical trials using KSM-66 ashwagandha at recommended doses have reported it to be safe and well-tolerated with minimal side effects.

The key is taking the right form, at the right dose, consistently. Most side effects people experience come from taking too much, taking it on an empty stomach, or using a low-quality product with inconsistent potency.

Common Side Effects

Upset Stomach or Nausea

This is the most commonly reported side effect and it's almost always linked to taking ashwagandha on an empty stomach. The fix is simple: take it with food or a small snack. Most people find this eliminates the issue completely.

Drowsiness

Ashwagandha has a naturally calming effect. Some people — particularly those who are sensitive to adaptogens may feel slightly drowsy when they first start taking it, especially if they take it during the day.

If this happens, switch to taking it in the evening before bed. The calming effect then works in your favour rather than against you.

Loose Stools or Digestive Discomfort

At higher doses, ashwagandha can occasionally cause loose stools or mild digestive discomfort. This is more common when starting out and usually settles after the first week or two as your body adjusts.

Starting with a lower dose and building up gradually helps avoid this.

Headache

A small number of people report mild headaches when they first start taking ashwagandha. This typically passes within the first week. Staying well hydrated helps.

Serious Side Effects: Rare But Important to Know

Serious side effects from ashwagandha are rare at recommended doses, but they have been reported:

Liver Issues

A small number of case reports have linked ashwagandha supplements to liver injury. These cases are rare and mostly involved very high doses or poor-quality products. A 2020 review in Basic & Clinical Pharmacology & Toxicology noted that while liver reactions are uncommon, people with existing liver conditions should be cautious.

If you notice yellowing of the skin or eyes, dark urine, or unusual fatigue — stop taking ashwagandha immediately and speak to your GP.

Thyroid Hormone Changes

Ashwagandha may increase thyroid hormone levels in some people. For most this is not a problem, but for anyone already on thyroid medication it could cause levels to go too high. Always speak to your GP before taking ashwagandha if you have a thyroid condition.

Who Should Avoid Ashwagandha

Pregnant Women

Ashwagandha should be avoided during pregnancy. Some research suggests it may stimulate uterine contractions, which could be harmful. Do not take ashwagandha if you are pregnant.

Breastfeeding Women

There is not enough research on ashwagandha during breastfeeding to confirm it is safe. Avoid it until more evidence is available and consult your midwife or GP.

People With Thyroid Conditions

As mentioned above — ashwagandha may affect thyroid hormone levels. Anyone with hyperthyroidism, hypothyroidism, or who takes thyroid medication should speak to their GP before starting

People With Autoimmune Conditions

Ashwagandha can stimulate immune system activity. For people with autoimmune conditions — such as rheumatoid arthritis, lupus, or multiple sclerosis — this could potentially worsen symptoms. Speak to your doctor first.

People on Sedatives or Anti-Anxiety Medication

Ashwagandha has a calming effect on the nervous system. Combined with sedatives or certain anti-anxiety medications, this effect could be amplified. Always check with your pharmacist if you take any of these.

People With Liver Conditions

Given the rare reports of liver reactions, anyone with an existing liver condition should avoid ashwagandha or only take it under medical supervision.

How to Avoid Side Effects

Most side effects are easy to prevent:

•       Always take it with food — eliminates most stomach and nausea issues

•       Start with a lower dose — 300mg of KSM-66 extract per day to begin with

•       Take it in the evening — the calming effect works better for sleep and avoids daytime drowsiness

•       Choose a quality extract — KSM-66 is standardised and tested, reducing the risk of inconsistent potency

•       Don't exceed recommended doses — more is not better with ashwagandha

Why KSM-66 Has a Better Safety Profile

Not all ashwagandha is the same. Generic root powders have no guaranteed potency — meaning you don't know how much active compound you're actually getting. This inconsistency increases the risk of taking too much or too little.

KSM-66 is a standardised, clinically tested extract with a well-documented safety profile built across over 20 human trials. The clinical studies consistently report it as safe and well-tolerated at the recommended dose.

The Wish Fusion Ashwagandha KSM-66 uses this exact extract — no fillers, no artificial additives, GMP manufactured in the UK. If you are going to try ashwagandha, starting with a quality KSM-66 product minimises the risk of the side effects that are most commonly linked to poor-quality supplements.

For a full picture of what ashwagandha does and how it works, read our complete guide to ashwagandha health benefits. Or if you're just getting started, see what ashwagandha is and how it works.

Frequently Asked Questions

What are the most common side effects of ashwagandha?

The most common side effects are nausea or upset stomach — usually caused by taking it on an empty stomach — mild drowsiness, and occasional loose stools at higher doses. These are generally mild and can be avoided by taking ashwagandha with food, starting at a lower dose, and switching to evening use if drowsiness is an issue.

Is ashwagandha safe to take every day?

Yes, for most healthy adults, KSM-66 ashwagandha is safe for daily long-term use at recommended doses (300–600mg of extract per day). It is non-habit-forming and does not cause withdrawal. People with thyroid conditions, autoimmune disease, liver conditions, or those on medication should check with their GP first.

Who should not take ashwagandha?

Pregnant women should avoid ashwagandha entirely. People with thyroid conditions, autoimmune diseases, liver conditions, or those taking sedatives, anti-anxiety medication, or thyroid medication should speak to their GP before starting. Breastfeeding women should also avoid it until more safety data is available.

Can ashwagandha cause liver damage?

Liver reactions to ashwagandha are rare but have been reported in a small number of cases, mostly involving high doses or poor-quality products. If you have an existing liver condition, avoid ashwagandha or only take it under medical supervision. If you experience yellowing of the skin, dark urine, or unusual fatigue while taking ashwagandha, stop immediately and see your GP.

How long do ashwagandha side effects last?

Most initial side effects — such as mild nausea or digestive discomfort — settle within the first one to two weeks as your body adjusts. If side effects persist beyond two weeks or feel severe, stop taking ashwagandha and speak to your GP.