Ashwagandha (Withania somnifera) has become one of the most popular adaptogenic supplements worldwide, used for stress relief, sleep, and athletic performance. But rising popularity has outpaced public understanding of its safety profile. What side effects does ashwagandha actually cause, and when should you be concerned?
This article reviews the clinical evidence on ashwagandha side effects — from mild gastrointestinal discomfort to rarer but more serious concerns like thyroid disruption and liver injury — so you can make an informed decision about supplementation.
This article is for informational purposes only and does not constitute medical advice. Consult your physician before starting any supplement.
Public Perception vs. Clinical Reality
Despite ashwagandha's widespread use, public understanding of its safety profile remains uneven. Khalil and Aljohani (2026) at King Abdulaziz University conducted a mixed-methods study surveying Saudi adults about their knowledge, safety perceptions, and use patterns of ashwagandha. The study found that while many users were aware of ashwagandha's purported benefits, a significant portion lacked awareness of potential side effects and drug interactions.[2]
This gap between enthusiasm and informed use is concerning. Ashwagandha is generally well-tolerated in clinical trials lasting up to 12 weeks, but "generally well-tolerated" does not mean "free of side effects." The distinction matters — particularly for people taking medications, those with autoimmune conditions, or individuals using ashwagandha at doses exceeding what has been studied.
Common Side Effects Reported in Clinical Trials
Gastrointestinal Symptoms
The most frequently reported ashwagandha side effects in clinical trials are gastrointestinal in nature. These include:
- Nausea and stomach upset
- Diarrhea or loose stools
- Abdominal discomfort or cramping
- Bloating
These symptoms are typically mild, dose-dependent, and most common during the first one to two weeks of supplementation. They tend to resolve as the body adjusts. Taking ashwagandha with food rather than on an empty stomach often reduces gastrointestinal discomfort.
Obhrai, Shenoy, and Arora (2026) at Dayanand Medical College and Hospital conducted a randomized, double-blind, placebo-controlled trial (n=91) in postmenopausal women receiving 600 mg/day of ashwagandha root extract for 12 weeks. The study found that ashwagandha was generally well-tolerated, with only mild gastrointestinal complaints reported and no serious adverse events.[5]
Similarly, Naik et al. (2026) conducted a randomized, double-blind, placebo-controlled trial in children and adolescents (ages 6–17) with mild ADHD, using ashwagandha root extract for 8 weeks. The extract was reported to be safe and well-tolerated, with adverse event rates comparable to placebo.[8]
Drowsiness and Sedation
Because ashwagandha has documented effects on sleep quality, some users report daytime drowsiness — particularly at higher doses or when taken in the morning. Obhrai, Shenoy, and Arora (2026) found that ashwagandha significantly improved sleep quality in postmenopausal women, which confirms its sedative properties.[5] While improved sleep is a benefit for many, it also means the supplement can cause unwanted drowsiness if timing or dosing is not carefully managed.
Headache and Upper Respiratory Symptoms
Some clinical trials report headache and mild upper respiratory tract symptoms (nasal congestion, cough) in both ashwagandha and placebo groups at similar rates, suggesting these may not be directly caused by the supplement. However, they appear in adverse event reporting frequently enough to warrant mention. If you experience persistent headaches after starting ashwagandha, it is worth discussing with your healthcare provider.
Serious Safety Concerns: Thyroid, Liver, and Hormonal Effects
Thyroid Stimulation
One of the most clinically significant ashwagandha side effects is its potential to stimulate thyroid function. Multiple case reports and some clinical data suggest ashwagandha can increase thyroid hormone levels (T3 and T4) and decrease thyroid-stimulating hormone (TSH). This is particularly concerning for individuals with:
- Hyperthyroidism or Graves' disease
- Thyroid nodules
- Those already on thyroid medication (levothyroxine or methimazole)
For people with hypothyroidism not on medication, the thyroid-stimulating effect might seem beneficial, but self-medicating thyroid conditions with supplements is dangerous without medical monitoring. Thyroid levels should be checked before and during ashwagandha use if you have any thyroid disorder.
Liver Injury
Rare but serious cases of ashwagandha-induced liver injury have been reported in pharmacovigilance databases and case reports. These typically present with elevated liver enzymes, jaundice, and in severe cases, acute liver failure. The mechanism is not fully understood but may involve idiosyncratic reactions or contaminants in poorly manufactured products.
Warning signs of liver injury include:
- Yellowing of the skin or eyes (jaundice)
- Dark urine
- Extreme fatigue
- Upper right abdominal pain
- Loss of appetite
If any of these symptoms appear after starting ashwagandha, discontinue use immediately and seek medical attention.
Hormonal Effects
Ashwagandha has documented effects on testosterone, cortisol, and reproductive hormones. While increased testosterone may be desirable in some contexts, the hormonal activity raises concerns for hormone-sensitive conditions. Preliminary evidence suggests ashwagandha may influence estrogen receptor activity, which is relevant for individuals with hormone-receptor-positive cancers. Hahm, Kim, and Singh (2026) at the University of Pittsburgh investigated ashwagandha's role in breast cancer prevention using preclinical models, highlighting the herb's complex interaction with hormonal pathways. However, this was a preclinical study, and human clinical trials are still needed to understand the implications for cancer risk.
Special Populations: Who Should Avoid Ashwagandha
Pregnant and Breastfeeding Women
Ashwagandha is classified as potentially unsafe during pregnancy. Traditional Ayurvedic texts categorize it as an abortifacient at high doses. No adequate human safety data exists for use during pregnancy or lactation. Pregnant or breastfeeding women should avoid ashwagandha entirely.
Children and Adolescents
While limited data exists for pediatric use, Naik et al. (2026) conducted a rigorous randomized, double-blind, placebo-controlled trial evaluating ashwagandha root extract in children and adolescents aged 6–17 with mild ADHD over 8 weeks. The extract was well-tolerated with a safety profile comparable to placebo in this controlled setting.[8] However, this remains a single short-term study, and long-term safety data in children is lacking. Pediatric use should only occur under medical supervision.
Autoimmune Conditions
Ashwagandha is an immunomodulator that may stimulate immune activity. For individuals with autoimmune diseases such as lupus, rheumatoid arthritis, multiple sclerosis, or Hashimoto's thyroiditis, this immune stimulation could theoretically worsen symptoms or trigger flares. While clinical data on this specific risk is limited, the immunomodulatory mechanism warrants caution.
People Scheduled for Surgery
Because ashwagandha may affect blood pressure, blood sugar levels, and the central nervous system, most practitioners recommend discontinuing it at least two weeks before scheduled surgery to avoid interactions with anesthesia and other perioperative medications.
Drug Interactions and Contraindications
Ashwagandha has the potential to interact with several classes of medication. The Khalil and Aljohani (2026) study notably found that many ashwagandha users were unaware of potential drug interactions, underscoring the need for better education.[2]
Medications That May Interact With Ashwagandha
- Thyroid medications (levothyroxine, methimazole): Ashwagandha may alter thyroid hormone levels, potentially requiring dose adjustments.
- Sedatives and anxiolytics (benzodiazepines, zolpidem): Additive sedative effects may cause excessive drowsiness.
- Immunosuppressants (tacrolimus, cyclosporine, mycophenolate): Ashwagandha's immune-stimulating properties may counteract these medications.
- Antihypertensives: Ashwagandha may lower blood pressure, increasing the risk of hypotension.
- Diabetes medications (insulin, metformin, sulfonylureas): Ashwagandha may lower blood sugar, increasing hypoglycemia risk.
- Anticonvulsants: Some evidence suggests ashwagandha's bioactive compounds may interact with GABAergic pathways. Mahgoub et al. (2026) explored withanolide delivery systems for CNS targeting in a preclinical model and noted the compound's interaction with neurological pathways relevant to epilepsy.[1] While this was not a drug interaction study per se, the GABAergic activity of ashwagandha warrants caution when combining with anticonvulsant medications.
If you are taking any prescription medications, consult your physician or pharmacist before starting ashwagandha.
Dosing: What the Studies Used
Ashwagandha dosing in clinical trials has ranged widely, but most studies showing both efficacy and acceptable safety used the following doses:
- 300 mg twice daily (600 mg/day total): This is the most commonly studied dose for stress, anxiety, and sleep outcomes. Obhrai, Shenoy, and Arora (2026) used 600 mg/day of root extract in their 12-week trial in postmenopausal women, reporting good tolerability.[5]
- Pediatric dosing: Naik et al. (2026) used ashwagandha root extract in children and adolescents for 8 weeks, though specific dose-per-kg details varied by age group in their protocol.[8]
Key considerations for dosing and side effects:
- Root extract vs. whole plant: Most well-designed trials use standardized root extract, not whole-plant preparations. Root extract concentrates withanolides while excluding leaf compounds (withaferin A), which may have different toxicity profiles.
- Standardization: Look for products standardized to withanolide content, typically 2.5–5%. This ensures consistent dosing across batches.
- Duration: Most clinical trials last 8–12 weeks. Long-term safety data beyond 12 weeks is limited. Cycling ashwagandha (e.g., 8 weeks on, 2–4 weeks off) is a common practice, though formal evidence for this approach is sparse.
- Dose-response for side effects: Gastrointestinal side effects appear to increase at doses above 600 mg/day. Doses exceeding 1,200 mg/day have not been well-studied for safety.
Safety and Side Effects Summary
The overall safety profile of ashwagandha based on available clinical evidence can be summarized as follows:
| Side Effect | Frequency | Severity | Action |
|---|---|---|---|
| GI discomfort (nausea, diarrhea) | Common | Mild | Take with food; usually resolves in 1–2 weeks |
| Drowsiness | Common | Mild | Take in the evening; reduce dose if persistent |
| Headache | Occasional | Mild | Monitor; usually comparable to placebo rates |
| Thyroid changes | Uncommon | Moderate–Serious | Monitor thyroid labs; avoid with thyroid disorders |
| Liver injury | Rare | Serious | Discontinue immediately; seek medical attention |
| Hormonal disruption | Uncommon | Variable | Avoid with hormone-sensitive conditions |
What to Look For in a Supplement
Given that ashwagandha side effects can be influenced by product quality, form, and dosing, selecting the right supplement matters. Based on the clinical evidence reviewed above, here is what to consider:
- Root-only extract: Clinical trials showing favorable safety profiles — including Obhrai, Shenoy, and Arora (2026)[5] and Naik et al. (2026)[8] — used root extract specifically. Whole-plant or leaf-inclusive products may contain higher levels of withaferin A, which has a different safety profile. Look for products that clearly specify "root extract" on the label.
- Standardized withanolide content: Products should be standardized to at least 2.5% withanolides by HPLC. This ensures you are getting a consistent, clinically relevant dose of the active compounds.
- Dose matching clinical evidence: The most robust safety and efficacy data comes from studies using 300–600 mg/day of concentrated root extract. A supplement providing 300 mg per capsule allows flexible dosing within the studied range.
- Third-party testing: Given the rare but serious risk of liver injury — which may relate to contaminants or adulteration — choose products tested by independent labs (NSF, USP, or ConsumerLab). Third-party testing verifies the absence of heavy metals, pesticides, and microbial contamination.
- GMP certification: Manufactured in a facility that follows Good Manufacturing Practices, reducing the risk of contamination or inconsistent dosing.
- No unnecessary additives: Avoid products with excessive fillers, artificial colors, or proprietary blends that obscure the actual ashwagandha dose.
The Bottom Line
The evidence for ashwagandha's safety is moderate — clinical trials consistently show it is well-tolerated at doses of 300–600 mg/day for up to 12 weeks, with most side effects being mild and gastrointestinal in nature. However, meaningful risks exist for specific populations, particularly those with thyroid disorders, autoimmune conditions, hormone-sensitive cancers, or those taking sedatives, immunosuppressants, or blood sugar–lowering medications. The most practical takeaway is that ashwagandha is not a universally safe supplement — it requires the same informed approach you would apply to any pharmacologically active compound. People under significant stress, postmenopausal women, and otherwise healthy adults seeking sleep or anxiety support represent the populations best-studied and most likely to benefit within an acceptable risk profile.
Frequently Asked Questions
How quickly do ashwagandha side effects appear?
Gastrointestinal side effects — nausea, stomach upset, diarrhea — typically appear within the first few days to two weeks of starting supplementation. They often resolve on their own. More serious effects like thyroid changes may develop gradually over weeks to months and require lab monitoring to detect. If you notice jaundice, dark urine, or severe fatigue at any point, discontinue immediately and consult a doctor.
Can ashwagandha damage the liver?
Rare cases of ashwagandha-associated liver injury have been documented in pharmacovigilance reports. Most occurred with prolonged use or high doses, and some may have involved contaminated products. While the overall risk is low in short-term clinical trials, choosing a third-party tested product and using ashwagandha for defined periods (8–12 weeks) with breaks may reduce this risk. Anyone with pre-existing liver disease should avoid ashwagandha or use it only under medical supervision.
Is ashwagandha safe for children?
Naik et al. (2026) demonstrated acceptable short-term safety in children aged 6–17 with mild ADHD over 8 weeks in a randomized, placebo-controlled trial.[8] However, this is limited evidence from a single study. Long-term safety in children has not been established. Pediatric use should only occur under the guidance of a healthcare provider.
Should I stop ashwagandha before surgery?
Yes. Because ashwagandha may affect blood pressure, blood sugar, and central nervous system activity, most practitioners recommend discontinuing it at least two weeks before any scheduled surgery. Its sedative properties could interact with anesthesia, and its blood sugar–lowering effects could complicate perioperative glucose management. Always inform your surgical team about all supplements you take.
Can ashwagandha interact with my thyroid medication?
Yes, this is one of the most clinically relevant drug interactions. Ashwagandha has been shown to increase thyroid hormone production, which could alter the effectiveness of levothyroxine (for hypothyroidism) or methimazole (for hyperthyroidism). If you have any thyroid condition, discuss ashwagandha with your endocrinologist and have thyroid function tested at baseline and after 4–6 weeks of use.
- Khalil AI, Aljohani AF, "Public knowledge, safety perceptions, and use patterns of ashwagandha (Withania somnifera) among Saudi adults: a mixed-methods study," Frontiers in Pharmacology, 2026. DOI: https://doi.org/10.3389/fphar.2026.1848763
- Obhrai S, Shenoy S, Arora M, "Effects of Withania somnifera root extract on sleep quality, body composition, and menopausal symptoms in postmenopausal women: a randomized, double-blind, placebo-controlled trial," Menopause, 2026. DOI: https://doi.org/10.1097/GME.0000000000002894
- Naik S, Muralidhar G, Rao BS et al., "Efficacy and safety of ashwagandha root extract in children and adolescents with mild attention-deficit/hyperactivity disorder: a randomized, double-blind, placebo-controlled trial," Journal of Medicine and Life, 2026. DOI: https://doi.org/10.25122/jml-2026-0025
