Ashwagandha can cause headaches through several biological mechanisms, from shifting your thyroid hormone levels to changing how your blood vessels dilate. Headache is listed as a known side effect by the Merck Manual, and while large clinical trials haven’t flagged it as common, individual responses vary based on your dosage, your biology, and what else you’re taking.
The good news: once you identify the mechanism behind your headache, the fix is usually straightforward.
Thyroid Stimulation Is a Leading Suspect
Ashwagandha directly stimulates the thyroid gland. In animal studies, 20 days of ashwagandha root extract increased the thyroid hormone T4 by roughly 111% and T3 by about 18%. For most people with normal thyroid function, this nudge is mild. But if your thyroid is already on the higher end of normal, or if you’re taking thyroid medication, ashwagandha can push you into a state of excess thyroid hormone.
That excess, called thyrotoxicosis, reliably produces headaches. A case report published in Cureus documented a patient who developed classic thyrotoxicosis symptoms after taking ashwagandha: fatigue, fever, weight loss, diarrhea, and headache. The headache resolved after stopping the supplement and receiving supportive care. If your headaches come with a racing heart, feeling overheated, or unexplained weight changes, thyroid stimulation is the most likely explanation.
Blood Vessel Dilation
Ashwagandha increases production of nitric oxide, a molecule that relaxes blood vessel walls. Lab studies show it boosts nitric oxide in a dose-dependent way, meaning higher concentrations produce more of it. This vasodilation is part of why ashwagandha is studied for blood pressure and heart health, but it’s also the same mechanism behind many common headache types.
When blood vessels in and around the brain widen, the surrounding nerves can become sensitized, producing a throbbing or pulsing headache. If your ashwagandha headaches feel similar to the kind you get from red wine, hot weather, or other vasodilators, this pathway is probably involved. People already prone to migraines or vascular headaches may be more susceptible.
Blood Sugar Drops
Ashwagandha lowers blood sugar levels. For people with diabetes, the Merck Manual specifically warns that combining it with glucose-lowering medications can push blood sugar too low. But even without diabetes, taking ashwagandha on an empty stomach or alongside a low-carb meal could dip your blood sugar enough to trigger a headache.
Hypoglycemia headaches tend to feel dull and diffuse, often accompanied by lightheadedness, irritability, or shakiness. If your headache consistently shows up when you take ashwagandha before eating, try taking it with a meal that includes some carbohydrates and protein.
GABA Activity in the Brain
Ashwagandha acts directly on GABA receptors, the same brain receptors targeted by anti-anxiety medications and sleep aids. Research published in the Journal of Ethnopharmacology confirmed that ashwagandha’s water extract activates two types of GABA receptors, with one subtype being 27 times more sensitive to it than the other.
This GABA activity is what gives ashwagandha its calming, sleep-promoting effects. But shifts in GABA signaling can also produce headaches, especially during the adjustment period when your brain is adapting to a new baseline. Some people experience this as a tension-type headache or a feeling of pressure. The effect can also work in reverse: if you’ve been taking ashwagandha regularly and suddenly stop, the rebound from reduced GABA stimulation may trigger headaches. A recent case report highlighted withdrawal-like symptoms after discontinuation, with symptoms resolving after supportive care.
Dosage and Product Quality
The commonly studied dose range is 300 to 600 mg of root extract per day, standardized to about 5% withanolides (the active compounds). Many commercial products exceed this, and because ashwagandha supplements use different extraction methods and standardization processes, the actual potency varies widely between brands. The NIH notes that it’s difficult to identify specific recommended amounts precisely because of this inconsistency. If you’re taking more than 600 mg daily, or using a concentrated extract, you’re more likely to experience side effects including headaches.
Product contamination is another real concern. The FDA has warned that Ayurvedic products, including herbal supplements, sometimes contain undisclosed heavy metals like lead, mercury, and arsenic. Chronic exposure to these metals causes symptoms including headaches, dizziness, fatigue, and gastrointestinal problems. If you’re using a bargain brand or an imported product without third-party testing, contamination could be contributing to your symptoms. Look for products that carry a USP, NSF, or ConsumerLab seal.
Medication Interactions That Raise Risk
If you’re taking other medications, the headache may not be from ashwagandha alone but from how it interacts with your existing prescriptions. The NIH identifies several drug categories that interact with ashwagandha:
- Thyroid medications: Ashwagandha’s thyroid-stimulating effect can amplify your prescription dose, creating excess thyroid hormone and associated headaches.
- Blood pressure medications: Combined with ashwagandha’s vasodilatory effects, blood pressure could drop too low, causing headaches and dizziness.
- Diabetes medications: Doubled glucose-lowering effects increase the risk of hypoglycemia headaches.
- Sedatives and anticonvulsants: Stacking these with ashwagandha’s GABA activity can amplify neurological side effects.
How to Narrow Down Your Cause
Pay attention to timing. A headache within one to two hours of taking ashwagandha points toward blood sugar changes or vasodilation. A headache that builds over days or weeks of use suggests thyroid shifts or cumulative effects. A headache that appears after you stop taking it suggests GABA-related rebound.
Try cutting your dose in half for a week. If the headaches disappear or diminish, the issue is dose-dependent, and your body may tolerate a lower amount. If they persist at any dose, ashwagandha likely triggers one of the biological pathways that your particular physiology is sensitive to, and a different adaptogen or approach to your original concern may be a better fit.
Switching brands can also help rule out contamination or differences in extract potency. Choose a product with third-party testing and a clearly stated withanolide percentage, and compare your experience over at least a week on the new product before drawing conclusions.