Ashwagandha Side Effects: What the Evidence Shows and Who Should Avoid It
Ashwagandha has a good safety profile in clinical trials at recommended doses — but it isn't appropriate for everyone. This article covers what the evidence actually shows on side effects, the genuine contraindications, and how to minimise risk if you do take it.
Side Effects in Clinical Trials
Clinical trials using KSM-66 (300-600mg daily for up to 6 months) consistently show ashwagandha is well-tolerated by the majority of participants. The most commonly reported side effects:
- Digestive: Nausea, loose stools, stomach discomfort — occurs in approximately 5-10% of users, almost entirely preventable by taking with food
- Drowsiness: Particularly at higher doses or in people sensitive to GABA-active compounds. Evening dosing resolves this for most users
- Headache: Reported in a small minority, usually resolving within the first 1-2 weeks
- Initial stimulation: Some people experience temporary agitation or worsened anxiety when starting — particularly those with a sensitised nervous system. Starting with 150mg and titrating up over 4 weeks prevents this
Serious but Rare: Liver Injury
A small number of case reports (fewer than 20 cases documented globally as of 2026) describe ashwagandha-associated liver injury — ranging from mild enzyme elevation to severe hepatitis. These appear to be idiosyncratic reactions (unpredictable, not dose-dependent) similar to rare reactions seen with other supplements and medications.
What to watch for: Jaundice (yellowing of skin or eyes), dark urine, light-coloured stools, right upper abdominal pain, unusual fatigue. Stop ashwagandha and seek medical attention immediately if these develop.
Risk context: Clinical trials at 300-600mg KSM-66 for up to 6 months found no significant liver enzyme changes. The risk appears low but is real — this is why quality standardised extracts and standard doses matter.
Who Should Avoid Ashwagandha
Pregnancy: Avoid entirely. Traditional texts and some animal evidence suggest potential uterine-stimulating effects. No adequate human safety data in pregnancy.
Hyperthyroidism / Graves disease: Ashwagandha can increase T3 and T4 thyroid hormone levels. In people with already elevated thyroid hormones, this can worsen symptoms. Get thyroid levels tested before supplementing if thyroid disease is a concern.
Autoimmune conditions: Lupus, rheumatoid arthritis, multiple sclerosis, Hashimoto's thyroiditis. Ashwagandha's immune-stimulating properties could theoretically worsen autoimmune activity. Use only under medical supervision.
Nightshade sensitivity: Ashwagandha (Withania somnifera) is in the Solanaceae (nightshade) family. People with documented nightshade sensitivity or allergy should avoid it or start with very low doses under observation.
Pre-surgery: Stop 2 weeks before any planned surgery — may potentiate anaesthetic and sedative medications.
Drug Interactions
Thyroid medication: Ashwagandha may increase thyroid hormone levels — can reduce the required dose of thyroid medication. Monitor thyroid levels if combining.
Immunosuppressants: May counteract immunosuppressive drugs (tacrolimus, cyclosporine). Avoid combining.
Sedatives / CNS depressants: Additive sedation with benzodiazepines, sleep medications, antihistamines. Use caution and separate timing.
Diabetes medication: Ashwagandha has mild blood sugar-lowering effects. May enhance the effect of diabetes medication — monitor blood glucose.
Blood pressure medication: Ashwagandha mildly lowers blood pressure. May have additive effect with antihypertensives — monitor.
How to Take Ashwagandha Safely
Start at 150-300mg KSM-66 daily with food. Increase to 600mg after 2-4 weeks if tolerated. Take in the evening to use any sedative effect beneficially. Cycle use (8-12 weeks on, 4 weeks off) for long-term use. Stop immediately if any liver-related symptoms develop.
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Frequently Asked Questions
What are the common side effects of ashwagandha?
At recommended doses (300-600mg KSM-66), the most common side effects are digestive upset (nausea, loose stools — preventable by taking with food), drowsiness at higher doses (manageable with evening dosing), and headache in a small minority. Serious but rare: liver injury (stop immediately if jaundice or dark urine develops). Clinical trials up to 6 months at standard doses report good overall tolerability in most participants.
Who should NOT take ashwagandha?
Avoid if: pregnant, hyperthyroid or have Graves disease, have autoimmune conditions (lupus, RA, MS), have nightshade allergy, or are scheduled for surgery within 2 weeks. Use with medical supervision if taking thyroid medication, immunosuppressants, benzodiazepines or diabetes medication. These are genuine contraindications based on mechanism — not theoretical concerns.
Can ashwagandha cause liver damage?
Rare idiosyncratic liver injury cases have been documented (fewer than 20 globally as of 2026). These appear unpredictable and not clearly dose-related. Standard dose clinical trials (300-600mg for up to 6 months) found no liver enzyme changes. Watch for jaundice, dark urine, abdominal pain — stop immediately and seek medical care if these develop. The absolute risk at standard doses is low but real enough to take the warning signs seriously.
Does ashwagandha make you sleepy?
Ashwagandha has mild sedative properties that can cause drowsiness, particularly at higher doses (600mg+). For most people this is subtle or absent. Taking in the evening turns this into a benefit (better sleep quality). If daytime sleepiness is a concern, take your full dose at dinner. The sedation is dose-dependent — starting at 150-300mg minimises this effect during the dose-finding period.