09/04/2026
Two Viburnums sit in most dispensaries, and they are not interchangeable.
Viburnum opulus (Cramp Bark) and Viburnum prunifolium (Black Haw) both get reached for on the same complaint. But the tissue picture that suits each one differs, and the distinction holds up in practice.
Black Haw is root bark, not stem bark, and it carries scopoletin, aesculetin, viburnin and a notable tannin fraction alongside its salicylates. The coumarin constituents relax uterine smooth muscle. The tannins add astringency the way Cramp Bark does not.
That astringency is the selection point. Where the picture is acute spasm in otherwise sound tissue, Cramp Bark is the closer fit. Where spasm sits alongside laxity, heaviness, and flooding rather than simple cramping, Black Haw covers both actions in one extract.
The Eclectics used it across a longer arc than a single painful day, and that reflects how the root bark behaves: slower to act than Cramp Bark, steadier once established, better in courses than in single doses.
Plant part matters here more than usual. Root bark is the traditional article. Stem bark from the same species is a substitution, not an equivalent, and the salicylate content puts it in the same conversation as aspirin sensitivity.
Pairs sensibly with Achillea millefolium where flooding dominates, and with Dioscorea villosa where the spasm has a colicky, gripping quality.
Where do you draw the line between the two Viburnums in your own prescribing, on tissue tone or on timing?