Does black walnut hull raise or lower blood pressure?

No trial has tested black walnut hull's effect on blood pressure in people, in either direction. The closest research measured juglone — one of the hull's compounds — injected into animals or applied directly to an isolated blood vessel, not a hull extract taken by mouth. That's a meaningfully different test than the question being asked.

What the evidence doesn't support

It doesn't support black walnut hull, taken by mouth, raising blood pressure. It doesn't support it lowering blood pressure either. And it doesn't support using it in place of a prescribed blood pressure medication, or alongside one without a doctor's input — no interaction study exists for that combination.

What the trials found

No human trial, and no oral-dosing animal trial, has measured black walnut hull's effect on blood pressure. What exists instead is pharmacology research on juglone, the hull's naphthoquinone pigment compound, isolated and tested outside the context of the whole hull or a supplement dose.

In one study, researchers injected juglone directly into the bloodstream of normotensive and hypertensive rats and measured a drop in mean arterial pressure, reduced further in the rats with high blood pressure than in the normal ones; the effect was blunted when the rats were pretreated with a drug that blocks nitric oxide production, and juglone also relaxed isolated rat aortic rings, pointing to a nitric-oxide and calcium-channel mechanism. In a separate study, researchers applied juglone directly to segments of isolated pig coronary artery and found it relaxed the vessel in a dose-dependent way, again through a nitric-oxide-dependent pathway. Both are real, useful pharmacology findings — and both are about isolated juglone, injected or applied directly to a blood vessel, in animals, not about a person swallowing a hull capsule or tincture. Nothing in either study establishes what oral black walnut hull does to a person's blood pressure, or even how much juglone an oral dose actually delivers into the bloodstream.

If anything, this research points away from raising blood pressure and toward relaxing blood vessels — but "points away from" is not the same as "shown to lower," and no study has tested that in a form or dose anyone actually takes.

Questions people ask

Does black walnut hull raise blood pressure?

No trial has tested that. The indirect animal research on juglone, its main compound, points the opposite direction — toward relaxing blood vessels, not constricting them — but that's not the same as a tested effect on an actual dose taken by mouth.

Does black walnut hull lower blood pressure?

Also untested directly. Isolated juglone lowered blood pressure when injected into rats and relaxed an isolated artery in lab conditions, but no study has given black walnut hull by mouth and measured blood pressure in a person or an animal.

Is black walnut hull safe to take with blood pressure medication?

That combination hasn't been studied. Ask a doctor or pharmacist before combining any herbal supplement with a blood pressure prescription. See black walnut hull interactions.

When to talk to a doctor

High or unstable blood pressure calls for a doctor's care — monitoring and, when appropriate, prescription medication — not an unstudied herbal supplement. Black walnut hull is not a treatment for high blood pressure, and nothing in the animal research above establishes that it changes blood pressure in a person at all. Talk to a doctor before starting it if you have diagnosed high blood pressure or take medication for it.

Related reading: black walnut hull: what the research does and doesn't show, black walnut hull interactions, and who should not take black walnut hull.