KSM-66 is generally safe for healthy adults when taken at standard doses. A 12-month observational study of healthy adults taking 600 mg daily found no serious adverse events and no harmful changes to liver, kidney, or thyroid function. That said, KSM-66 is not risk-free for everyone, and certain health conditions, medications, and life stages change the safety picture significantly.
What the Longest Safety Study Found
Most ashwagandha studies run 8 to 12 weeks, which leaves a gap for people planning to take it long-term. The most relevant data comes from a prospective, multicenter observational study that followed healthy adults (ages 18 to 65) taking 600 mg of KSM-66 daily for a full year. Over that period, 18 mild adverse events were recorded: nausea in about 3% of participants, abdominal pain in 1.6%, headaches in 1.6%, and occasional vomiting, dizziness, or diarrhea. All resolved on their own without treatment.
Importantly, the study tracked liver enzymes, kidney markers, and thyroid function throughout, and none of those shifted in a concerning direction. The researchers concluded KSM-66 was safe for 12 months of continuous use in this population. The key qualifier: these were healthy adults with no major pre-existing conditions.
The Liver Toxicity Question
Liver injury is the most commonly raised safety concern with ashwagandha, and there are real case reports behind it. The Netherlands Pharmacovigilance Centre has collected multiple reports of liver problems in people taking ashwagandha products, including several cases specifically involving KSM-66 branded supplements. In one case, a woman in her 30s developed abnormal liver function after five months of taking one KSM-66 capsule daily. In another, a man in his 50s developed hepatitis after two months on three capsules per day. A third case involved liver damage and fatty liver disease with an unknown timeline.
These are individual case reports, not controlled studies, and that distinction matters. Some of these people were taking other medications that could have contributed. The Dutch pharmacovigilance center also noted that herbal products can contain unlabeled ingredients or contaminants that might explain some cases. Still, the NIH Office of Dietary Supplements acknowledges at least five documented cases of people experiencing signs of liver injury while taking ashwagandha at doses of 450 to 1,350 mg daily over periods ranging from one week to four months.
The practical takeaway: liver injury from KSM-66 appears rare, but it’s not impossible. If you develop unusual fatigue, dark urine, yellowing skin, or upper abdominal pain while taking it, stop and get your liver checked.
Dosage Range Used in Studies
Clinical trials using KSM-66 specifically have tested doses between 250 and 600 mg per day of root extract. An international taskforce convened by the World Federation of Societies of Biological Psychiatry provisionally recommends 300 to 600 mg daily (standardized to 5% withanolides) for anxiety. Several studies found that 500 to 600 mg per day produced better results than lower doses.
Beyond that range, risks appear to climb. The liver injury cases documented by the NIH involved people taking up to 1,350 mg daily. Three case reports of thyroid overactivity (thyrotoxicosis) in women have also been linked to ashwagandha, with one case involving an unusually high dose of 1,950 mg per day for more than two months. Sticking to 600 mg or less per day aligns with the dosing that has the strongest safety data behind it.
Who Should Avoid KSM-66
The National Center for Complementary and Integrative Health (NCCIH) identifies several groups who should not take ashwagandha, including KSM-66:
- People with autoimmune conditions. Ashwagandha stimulates immune activity, which can worsen conditions like lupus, rheumatoid arthritis, or multiple sclerosis where the immune system is already overactive.
- People with thyroid disorders. Ashwagandha can raise thyroid hormone levels. If you have hyperthyroidism or are on thyroid medication, this creates a real risk of thyroid hormone excess.
- People scheduled for surgery. Its effects on blood pressure, blood sugar, and sedation make it a concern in the perioperative period.
- Pregnant or breastfeeding women. Despite ashwagandha’s long history of traditional use, there is essentially no reliable clinical data on its safety during pregnancy or lactation. Researchers at the InfantRisk Center have noted that even after reviewing hundreds of pages of literature, they could not find substantiated safety data for these populations.
Medication Interactions
KSM-66 can amplify or interfere with several categories of medication. The NCCIH lists interactions with diabetes drugs, blood pressure medications, immunosuppressants, sedatives, anti-seizure medications, and thyroid hormones.
The blood sugar interaction is straightforward: ashwagandha can lower blood glucose on its own, so combining it with insulin or other diabetes drugs risks pushing your levels too low. The same stacking effect applies to blood pressure. If you’re already on a beta blocker, ACE inhibitor, or similar medication, adding ashwagandha could drop your blood pressure further than intended.
For anyone on immunosuppressants after an organ transplant or for an autoimmune condition, ashwagandha works against the purpose of those drugs by boosting immune function. And its mild sedative properties can compound the effects of sleep aids, benzodiazepines, or anti-seizure medications.
Common Side Effects
At standard doses, KSM-66’s side effects are mostly digestive. Nausea is the most frequent, followed by abdominal discomfort, loose stools, and occasional headaches. In the year-long study, fewer than 10% of participants reported any side effect at all, and none were serious enough to require medical treatment. Some people find that taking it with food rather than on an empty stomach reduces stomach upset.
Drowsiness is another commonly reported effect, which is a feature for people taking it at bedtime for sleep but a drawback for daytime use. If you notice excessive sleepiness, shifting your dose to the evening usually solves the problem.