Black Haw

Black haw bark contains salicin (a salicylate precursor similar to that in willow bark) and the coumarin scopoletin, which has documented smooth-muscle relaxant and in-vitro platelet-inhibiting effects. Additive antiplatelet activity plus displacement of warfarin from plasma proteins by salicylates can increase bleeding risk and elevate INR.

Avoid concurrent use. If unavoidable, check INR within 3–5 days of initiation/discontinuation and counsel the patient to report bruising, gum bleeding, or haematuria. Discontinue black haw at least 2 weeks before any elective surgery.

Black haw bark contains salicin, which is metabolised to salicylic acid in vivo. Additive salicylate load increases the risk of GI mucosal injury, tinnitus, and bleeding in aspirin-treated patients, and may trigger hypersensitivity reactions (bronchospasm, urticaria, angioedema) in aspirin-sensitive asthmatics.

Do not combine in patients with aspirin hypersensitivity, NSAID-exacerbated respiratory disease (AERD/Samter's triad), or active peptic ulcer disease. For low-dose cardioprotective aspirin users, avoid or use the lowest effective black haw dose and monitor for bleeding.

The salicin content of black haw adds to COX-1 inhibition produced by NSAIDs, increasing the risk of upper GI bleeding, platelet dysfunction, and renal afferent-arteriolar vasoconstriction. Oxalic acid in the bark may also increase renal tubular crystal formation under dehydration.

Avoid chronic concurrent use, particularly in the elderly or patients with GI, renal, or cardiovascular disease. Prefer acetaminophen for mild pain if an analgesic is needed alongside black haw.

Scopoletin, a key coumarin constituent of V. prunifolium, relaxes smooth muscle and has been reported to inhibit platelet aggregation in vitro. Additive inhibition with clopidogrel increases bleeding risk, particularly peri-procedurally.

Discontinue black haw at least 14 days before any planned surgery, endoscopy with biopsy, or neuraxial anesthesia. Avoid with dual antiplatelet therapy. Report unusual bruising immediately.

Black haw has traditional and in-vivo uterine/vascular spasmolytic effects and is used as a mild hypotensive. Additive vasorelaxation with calcium channel blockers may produce symptomatic hypotension or dizziness, especially in elderly patients.

Start at low herbal doses, monitor home BP, and rise slowly to reduce orthostatic symptoms. Dose-reduce antihypertensive if symptomatic hypotension develops.

Black haw bark contains oxalic acid (oxalate) which chelates divalent cations. Concurrent ingestion reduces the intestinal absorption of iron, calcium, and zinc from foods and supplements.

Separate ingestion of oral iron and black haw by at least 2 hours. Monitor ferritin and Hb in patients on iron replacement who use black haw chronically.

Black haw historically used as a uterine tonic and for threatened miscarriage; it exerts uterine smooth-muscle relaxation via scopoletin and iridoid glycosides and has theoretical hormonal activity. Interaction potential with hormone replacement and contraceptive steroids is poorly characterised but plausible.

Theoretical only: maintain contraceptive vigilance (barrier backup if breakthrough bleeding occurs) and avoid high-dose black haw during pregnancy (possibly unsafe — uterine activity).