A daily dose of 600 mg of ashwagandha root extract is generally considered safe for most adults and falls within the range used in clinical trials. An international taskforce created by the World Federation of Societies of Biological Psychiatry and the Canadian Network for Mood and Anxiety Treatments provisionally recommends 300 to 600 mg daily of root extract (standardized to 5% withanolides) for generalized anxiety. That said, “safe in studies” comes with important caveats worth understanding before you start taking it.
Why 600 mg Is a Common Dose
Most clinical trials on ashwagandha use doses between 250 and 600 mg per day, and several have found that benefits are more pronounced at the higher end of that range. Sleep studies, for example, found that ashwagandha had a small but significant effect on sleep quality compared to placebo, with the strongest results at 600 mg daily taken for at least 8 weeks. Similar patterns show up in anxiety research.
So 600 mg isn’t an aggressive or experimental dose. It’s the upper boundary of what’s been studied in controlled settings, typically using standardized root extracts like KSM-66.
Common Side Effects
The most frequently reported side effects are digestive: stomach upset, diarrhea, and occasionally vomiting. Some people also experience drowsiness, which can actually be useful if you’re taking it for sleep but inconvenient if you’re dosing in the morning. These effects tend to be mild, and starting at a lower dose (300 mg) for the first week or two can help your body adjust.
Thyroid Hormone Changes
Ashwagandha can raise levels of thyroid hormones T3 and T4, likely through its effects on the body’s stress response system. For someone with an underactive thyroid, this might sound appealing, but it also means ashwagandha can interfere with thyroid medications or push hormone levels out of range. If you have an overactive thyroid (hyperthyroidism), ashwagandha is one to avoid entirely, since boosting those hormones further could worsen symptoms like rapid heart rate, weight loss, and anxiety.
Even if your thyroid function is normal, it’s worth knowing this effect exists. If you’re on thyroid medication and start taking ashwagandha, your blood work could shift enough that your dosage needs adjusting.
Rare but Serious Liver Concerns
A small number of case reports have linked ashwagandha to liver injury. In a review published in Pharmaceuticals, reported cases involved daily doses ranging from 450 to 1,350 mg, with durations from a few weeks to over a year. One case involved a 36-year-old man who took 450 mg three times daily (1,350 mg total) for six months before developing nausea, itching, and dark urine. Another involved a 30-year-old woman who developed itching after just 45 days at 450 mg. One case in the United States progressed to acute liver failure requiring a transplant.
These are rare, idiosyncratic reactions, meaning they’re unpredictable and don’t follow a simple dose-response pattern. But they’re worth knowing about. If you notice unusual fatigue, dark urine, yellowing skin, or upper abdominal pain while taking ashwagandha, stop and get your liver function checked.
How Long Has It Been Studied?
Most clinical trials run for 8 to 12 weeks, which means long-term safety data beyond a few months is limited. The provisional recommendation from the 2022 international taskforce explicitly noted that more research is needed. If you plan to take ashwagandha continuously for many months, you’re moving beyond what’s been well-studied in controlled settings.
Some practitioners suggest cycling off periodically (for instance, taking a break every two to three months), though there’s no clinical trial specifically validating that approach. It’s a precautionary measure rooted in the fact that we simply don’t have long-duration safety data.
Product Quality Matters
Ashwagandha is a dietary supplement, which means it isn’t subject to the same pre-market testing the FDA requires for prescription drugs. Some ayurvedic products have been found to contain heavy metals like lead, mercury, and arsenic, often without listing them on the label. The FDA has issued warnings after lab testing found high levels of lead and mercury in certain ayurvedic products sold online. Chronic exposure to these metals can cause high blood pressure, kidney damage, nerve problems, and gastrointestinal symptoms that could easily be mistaken for side effects of the herb itself.
To reduce this risk, look for products that carry third-party testing certifications (NSF International, USP, or ConsumerLab). Standardized extracts like KSM-66 or Sensoril are manufactured under tighter quality controls than generic ashwagandha powders, and they’re the forms most commonly used in clinical research.
Who Should Be Cautious
Pregnant and breastfeeding women are typically advised to avoid ashwagandha, as safety data in these populations is lacking. The same goes for people scheduled for surgery, since ashwagandha may affect sedation and blood pressure during anesthesia. People taking medications for diabetes, blood pressure, or thyroid conditions should be aware that ashwagandha can influence all three of those systems, potentially altering how well their medications work.
If you’re otherwise healthy, not pregnant, and not on medications that overlap with ashwagandha’s effects, 600 mg of a quality root extract daily is a well-studied dose that most people tolerate without issues. Starting lower and working up gives you a chance to catch any digestive sensitivity early.