Ashwagandha is not harmful for most healthy adults when taken at standard doses for short periods. Clinical trials using 300 to 600 mg of root extract daily have shown it to be well tolerated for up to about three months. But “not bad for most people” is not the same as “safe for everyone,” and there are real situations where ashwagandha can cause problems worth knowing about.
Common Side Effects
The most frequently reported side effects are digestive: stomach upset, diarrhea, and vomiting. Drowsiness is also common, which makes sense given that ashwagandha is traditionally classified as a calming herb. These effects tend to be mild, but they’re worth noting if you’re taking it for the first time or combining it with anything that also causes sedation.
The Liver Injury Question
Liver damage is the concern that gets the most attention, and the picture is more reassuring than alarming. Two separate meta-analyses, covering more than 1,100 healthy participants across 22 studies, found no effect on liver function from ashwagandha use. Liver injury does occur, but it’s rare and unpredictable, what toxicologists call “idiosyncratic.” The cases that have been reported vary widely in dose (from milligrams to grams), timing (anywhere from five days to over a year), and type of liver damage, which is the hallmark of a reaction driven by individual susceptibility rather than a consistent toxic effect.
A review of published case reports identified only five cases of liver injury linked to ashwagandha, and only one of those had definitive causality established. Many involved confounding factors like other medications, polyherbal products, or preexisting liver disease. One severe case did require a liver transplant, but all other patients recovered. No fatalities have been reported, and no regulatory authority has banned ashwagandha over liver concerns. That said, if you have existing liver disease, the German Federal Institute for Risk Assessment explicitly recommends avoiding ashwagandha supplements.
Thyroid Function Changes
Ashwagandha can meaningfully shift thyroid hormone levels. A clinical trial of 50 people with mildly underactive thyroids found that 600 mg daily for eight weeks lowered TSH (the hormone that signals your thyroid to work harder) while raising levels of both T3 and T4 (the active thyroid hormones). In plain terms, ashwagandha pushed their thyroid toward producing more hormones.
If you have a sluggish thyroid and aren’t on medication, this might sound like a benefit. But if you’re already taking thyroid medication, ashwagandha could throw off your dosage. And if your thyroid is overactive (hyperthyroidism), stimulating it further could make symptoms worse. Anyone on thyroid medication should be aware that adding or stopping ashwagandha may change how well their current dose works.
Autoimmune Conditions
Ashwagandha stimulates immune activity. For a healthy person, this is generally neutral or mildly beneficial. For someone with an autoimmune condition like lupus, rheumatoid arthritis, or multiple sclerosis, it’s a different story. As Memorial Sloan Kettering Cancer Center explains, the immune system in autoimmune disorders is already overactive, and ashwagandha can amplify that overactivity. If you have an autoimmune condition, this is one of the clearest reasons to avoid it.
Blood Sugar Effects
Ashwagandha lowers blood glucose. Human studies have confirmed that root powder reduces blood sugar in diabetic patients, and lab research shows it increases glucose uptake in muscle and fat cells in a dose-dependent way. For most people, a modest blood-sugar-lowering effect is harmless. But if you’re taking diabetes medication that already lowers blood sugar, stacking ashwagandha on top raises the risk of hypoglycemia, the shaky, dizzy feeling of blood sugar dropping too low.
Pregnancy and Breastfeeding
Ashwagandha has historically been used as an abortifacient, a substance intended to end pregnancy. There’s no modern clinical data confirming this effect, but there’s also no safety data for pregnant or breastfeeding women. The German Federal Institute for Risk Assessment recommends that pregnant women, breastfeeding mothers, and children avoid ashwagandha supplements entirely. The lack of evidence here is the problem: no one has studied it enough to say it’s safe for these groups.
Long-Term Use Is Unstudied
This is the most underappreciated gap. According to the NIH Office of Dietary Supplements, ashwagandha has been well tolerated in clinical trials lasting up to about three months. Beyond that, its long-term safety simply isn’t known. Most trials use doses between 240 and 1,250 mg per day of extract, and a joint international taskforce provisionally recommends 300 to 600 mg daily for anxiety. But “provisionally recommended for three months” is a long way from “safe to take indefinitely,” and many people use ashwagandha continuously for months or years without any long-term data to support that practice.
If you’re healthy, not pregnant, not on thyroid or diabetes medication, and don’t have autoimmune or liver issues, ashwagandha at standard doses for a few months is unlikely to cause harm. The people most at risk are those who don’t realize it interacts with their existing condition or medication. The supplement itself isn’t dangerous for most, but the assumption that “natural” means “can’t hurt” is where the real risk lives.