Ashwagandha and Thyroid: What the Trials and Case Reports Show

Does ashwagandha affect the thyroid? Yes, it can raise thyroid hormone levels. In a placebo-controlled trial in people with a slightly underactive thyroid, 600 mg a day for eight weeks lowered TSH and raised T3 and T4. That sounds like good news, but the same effect is a risk for anyone already on thyroid medicine or with an overactive thyroid: there are case reports of ashwagandha pushing people into thyrotoxicosis. If you have any thyroid condition, take it only with your doctor’s agreement and a plan to check your levels.

Ashwagandha is mostly bought for stress and sleep, not for the thyroid. But its effect on thyroid hormones is one of the best-documented side effects in the research, and the US National Institutes of Health lists thyroid medicine among its possible interactions.

The short version

• Effect: ashwagandha can increase thyroid hormones (T3 and T4) and lower TSH.
• Subclinical hypothyroidism: one 8-week trial of 50 adults found it moved thyroid tests toward normal. It is a single small trial.
• Hyperthyroidism or Graves’ disease: avoid it. Raising thyroid hormones is the opposite of what you need.
• On levothyroxine: the two may add up and push your levels too high. Only combine them with your doctor’s agreement and follow-up tests.
• Hashimoto’s: there are no trials. Talk to your doctor first.
• Warning signs: palpitations, a racing heart, tremor, anxiety, weight loss or heat intolerance. Stop and see a doctor.

How this article was done

I have not taken ashwagandha for this article, and there is no test panel. I read the NIH Office of Dietary Supplements fact sheet on ashwagandha, the placebo-controlled trial in subclinical hypothyroidism, and the published case reports of thyrotoxicosis. This is general information, not medical advice: thyroid conditions need individual care, and it follows my methodology.

What the research shows

The hypothyroidism trial

The key study is a 2018 double-blind, randomised, placebo-controlled trial in the Journal of Alternative and Complementary Medicine. It enrolled 50 adults aged 18 to 50 with subclinical hypothyroidism, meaning a raised TSH (4.5 to 10 μIU/mL) but no full thyroid disease. Half took 600 mg of ashwagandha root extract a day, half a placebo, for eight weeks.

Compared with placebo, ashwagandha significantly lowered TSH (p < 0.001) and raised T3 (p = 0.0031) and T4 (p = 0.0096). Side effects were mild and rare: one person on ashwagandha and three on placebo reported any. The authors concluded that ashwagandha may help normalise thyroid tests in this group.

Three limits matter. It is one small trial; it lasted only eight weeks; and it did not include people with full hypothyroidism or anyone on thyroid medicine. It is not evidence that ashwagandha can replace levothyroxine.

Small rises in people without thyroid disease

The NIH fact sheet also notes an earlier study in which three adult men who took 500 mg a day of an ashwagandha extract for eight weeks had small increases in T4. Most stress trials did not measure thyroid hormones at all, so how often this happens is not known.

Case reports of thyrotoxicosis

Thyrotoxicosis means too much thyroid hormone in the body. The NIH cites three case reports of it in women aged 32 to 73 who were taking ashwagandha. In one of them, published in Cureus in 2022, a 73-year-old woman with a history of hypothyroidism had used ashwagandha for two years and arrived at hospital with a racing heart, chest pain, tremor and a TSH below 0.01. Her symptoms resolved after she stopped ashwagandha, and her thyroid returned to its usual underactive state. In another case, the dose was unusually high, at 1,950 mg a day for more than two months. In all three, stopping ashwagandha resolved the problem.

Case reports cannot prove cause, and they are rare given how many people take ashwagandha. But they point the same way as the trial: ashwagandha can push thyroid hormones up.

Ashwagandha by thyroid condition

Your situation	What the evidence suggests
Normal thyroid	Probably fine at trial doses for up to about three months. Stop if you notice palpitations, tremor or unusual weight loss.
Subclinical hypothyroidism, no medicine	One small trial found it improved thyroid tests. Discuss with your doctor and recheck your levels.
Hypothyroidism on levothyroxine	Risk of levels going too high. Only with your doctor’s agreement and follow-up blood tests.
Hashimoto’s thyroiditis	No trials. Some experts are cautious because of possible effects on the immune system. Ask your doctor.
Hyperthyroidism or Graves’ disease	Avoid. It could make an overactive thyroid worse.
Pregnancy	Avoid. Some experts advise against ashwagandha in pregnancy for other reasons.

Can you take ashwagandha with levothyroxine?

Not without your doctor’s agreement. The NIH says the case reports suggest ashwagandha might interact with thyroid hormone medicines. The concern is simple: your levothyroxine dose was set to bring your hormones into range, and ashwagandha may push them higher on top of that. The result can be the symptoms of too much thyroid hormone, such as palpitations, anxiety, insomnia and weight loss, which can be mistaken for the stress you were trying to treat.

If your doctor agrees to a trial, the sensible approach is to keep everything else unchanged, use a standard dose rather than a high one, and ask whether to recheck your thyroid levels after a few weeks.

Ashwagandha and Hashimoto’s

There are no clinical trials of ashwagandha in Hashimoto’s thyroiditis, the most common cause of hypothyroidism. Most people with Hashimoto’s take levothyroxine, so the interaction concern above applies. The NIH also lists immunosuppressants among ashwagandha’s possible interactions, and some experts advise caution in autoimmune disease because ashwagandha may affect the immune system. Claims online that it “heals” Hashimoto’s are not backed by any trial.

Signs your thyroid is reacting

Stop ashwagandha and contact a doctor if you notice:

• A racing or irregular heartbeat, or palpitations
• Tremor or shaky hands
• New anxiety, irritability or insomnia
• Unexplained weight loss, sweating or feeling too hot
• Frequent or loose bowel movements

These match the symptoms in the published case reports. A simple blood test of TSH and free T4 shows whether your thyroid is involved.

If you still want to try ashwagandha

• Talk to whoever manages your thyroid first, and tell them the product and dose.
• Stick to trial doses (240–600 mg of root extract a day). High doses were involved in at least one case of thyrotoxicosis.
• Give it a time limit. The effects on stress appear at about eight weeks, and safety beyond three months is not known. See how long ashwagandha takes to work.
• Consider alternatives that do not affect the thyroid. L-theanine and magnesium are not known to change thyroid hormones; see L-theanine for anxiety and magnesium for anxiety. If you pair magnesium with ashwagandha, read magnesium and ashwagandha too, because magnesium can affect the absorption of some medicines. All the main options are ranked in best supplements for stress.

Choosing a product? Six popular ashwagandha supplements are compared on extract, dose against the trials and cost per day in the best ashwagandha supplement.

Common questions

Is ashwagandha bad for your thyroid?

Not for most people with a healthy thyroid, but it can raise thyroid hormone levels. That is a problem if you have an overactive thyroid or already take thyroid medicine.

Does ashwagandha help hypothyroidism?

One small 8-week trial in people with subclinical hypothyroidism found 600 mg a day improved TSH, T3 and T4 compared with placebo. There is no evidence it can replace thyroid medicine.

Can ashwagandha cause hyperthyroidism?

Rarely. There are case reports of thyrotoxicosis in people taking ashwagandha, including one at an unusually high dose, and all resolved after stopping it.

Can I take ashwagandha if I have Hashimoto’s?

There are no trials in Hashimoto’s. Because most people with it take levothyroxine and ashwagandha may affect the immune system, ask your doctor first.

Does ashwagandha affect thyroid blood tests?

It can, because it may change TSH, T3 and T4. Tell your doctor you take it before a thyroid test.

How long does it take for ashwagandha to affect the thyroid?

In the hypothyroidism trial, changes were measured after eight weeks. In one case report, problems appeared after long-term use.

Sources

• Sharma AK, Basu I, Singh S. Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial. Journal of Alternative and Complementary Medicine. 2018 — 50 adults, 600 mg a day, eight weeks.
• NIH Office of Dietary Supplements — Ashwagandha fact sheet for health professionals — thyroid findings, case reports, interactions and the three-month safety window.
• Kamal HI et al. Ashwagandha as a Unique Cause of Thyrotoxicosis Presenting With Supraventricular Tachycardia. Cureus. 2022 — the case of a 73-year-old woman.