What is Black Haw?

Black Haw is the bark of Viburnum prunifolium, a shrub that grows in the eastern United States. It is also called stagbush. The bark of the root and stem is dried and used in teas, tinctures and capsules.

It has one main folk use: cramping pain in the uterus (womb), above all period pain. Some products also aim it at muscle cramps and back pain during a period.

Here is the honest verdict. Human trials on Black Haw are almost absent, so its benefit is unproven. Long traditional use is not proof that a plant works, and it is not proof that it is safe.

The bark holds aspirin-like compounds and oxalic acid. That shapes who should stay away from it, which the safety section sets out.

How does Black Haw work?

No one has shown how Black Haw acts in the human body.

In lab tests on animal tissue, bark extracts relaxed strips of uterus (womb) muscle. That is a test-tube result. Whether the same thing happens in a woman drinking a tea has not been shown.

Scopoletin, one compound in the bark, eased smooth muscle spasm in animal work. The amounts used in such tests can be far above what a normal dose gives.

The bark also holds salicylates, the aspirin family of compounds. Aspirin itself dulls pain in people. The amount in a cup of bark tea is likely small, and no trial has linked it to pain relief.

So the proposed story is plausible. It is not proven.

What forms does Black Haw come in?

Black Haw is sold as dried bark from the root or the stem.

Common forms include:

Dried bark for a decoction, which means a long simmer in water.

Tincture, an alcohol extract taken in drops.

Capsules or tablets of powdered bark.

Mixed herbal blends sold for period pain, often with cramp bark (Viburnum opulus).

Strength varies widely between brands. Herbal products are not tested the way medicines are. A label that names the plant part and the amount per dose is more useful than one that does not.

Where it comes from:

Black Haw was a staple of American folk medicine and of the Eclectic physicians of the 1800s.

Home healers in the southern United States simmered the bark for cramping pain in the womb. Eclectic doctors later wrote it up as a uterine sedative, meaning they believed it calmed the womb muscle. It was listed in the United States Pharmacopoeia for many years.

It was also given in attempts to prevent miscarriage and to ease after-birth pains. Those uses were never put to a proper trial. They are not a reason to take it in pregnancy today.

What does Black Haw help with?

• Period pain (dysmenorrhoea, painful periods): This is the main use people buy it for. Folk and Eclectic writers described the bark as easing the gripping pain of a period. Animal tissue studies back the idea that extracts can relax womb muscle. There are no good human trials. Nobody has compared Black Haw with a dummy pill in women with period pain. Any relief you feel may be real, may be timing, or may be the placebo effect.
• Cramping back and leg pain during a period: Traditional writers extended the same cramp idea to the lower back and legs. No human study has tested this. Evidence here is weaker still than for period pain itself.
• After-birth cramping pains (historical use): Nineteenth-century practitioners gave the bark for cramps in the days after childbirth. There is no modern human evidence for this. It is not recommended while breastfeeding, because no one has shown what passes into milk.
• Threatened miscarriage, meaning bleeding in early pregnancy (historical use only): This historical use is the reason the plant is still talked about. It is not supported by evidence, and it is not safe to try. No trial has shown that Black Haw prevents miscarriage. Bleeding in early pregnancy needs urgent medical care, not a herb. If you are pregnant and bleeding, contact your midwife or doctor the same day.

What are the side effects of Black Haw?

• Upset stomach or nausea
• Vomiting after large amounts
• Diarrhoea
• Dry, puckering mouth from the tannins
• Rash or itching in people sensitive to aspirin
• Wheezing in people with aspirin-sensitive asthma
• Possible added kidney stone risk, because of the oxalic acid
• Possible easier bruising or bleeding, in theory, from the aspirin-like compounds

Good to know:

Most reported effects are mild stomach ones. Serious harm is rare in the published record.

But that record is thin. Few people have been studied in a careful way, so rare problems could be missed. Treat an unexpected symptom as a reason to stop.

How much Black Haw should you take?

• Recommended daily: This page gives label ranges only, not advice for you. Labels on dried bark often suggest about 1 to 2 grams for a single dose as a decoction. Tincture labels usually suggest a few millilitres, taken in water. Strengths differ a lot between brands, so one product's dose is not another's. Ask a pharmacist or doctor before you start, above all if you take any regular medicine.
• Best time of day: Time of day does not matter much. People who use it tend to take it when cramps start or just before a period is due.
• With or without food: Taking it with food is the gentler choice. The tannins and aspirin-like compounds can irritate an empty stomach.
• Time to effect: If anything happens, people report it within an hour or two. It may also do nothing at all. There is no trial evidence that it beats a dummy treatment, so no reliable time to effect can be given.
• How long to take it: It has traditionally been used for a few days around a period, not every day. No study has tested long-term use, so no safe long-term span can be stated. The aspirin-like compounds and the oxalic acid are the reason to keep use short. If you feel you need it month after month, that is a reason to get your period pain looked at properly.