Yarrow

Yarrow may increase stomach acid production through its bitter principle constituents and flavonoids that stimulate digestive secretions. By increasing gastric acid, yarrow may reduce the effectiveness of antacids and H2 blockers. Conversely, antacids may reduce the absorption of yarrow's active constituents.

Advise patients that yarrow and antacids work in opposing ways on gastric acid. Separate dosing by at least 2 hours to minimize interaction. Patients with peptic ulcer disease should avoid yarrow.

Yarrow contains coumarin-type compounds and flavonoids (apigenin, rutin) with antiplatelet activity, and it modulates CYP450 enzymes involved in warfarin metabolism (including CYP2C9 and CYP3A4). Net clinical effect is typically increased bleeding risk, though paradoxical decreases in INR have been reported.

Avoid combination when possible. If used concurrently, check INR within 1-2 weeks of initiation and monthly thereafter. Counsel patients on bleeding warning signs and to not suddenly stop yarrow without notifying anticoagulation service.

Yarrow has documented antiplatelet and mild anticoagulant activity via flavonoid and sesquiterpene constituents. Combined with NSAIDs, aspirin, clopidogrel, or heparin/LMWH this additively increases risk of bruising and bleeding.

Discontinue yarrow at least 2 weeks before elective surgery. Avoid in patients with thrombocytopenia, coagulopathy, or recent GI ulceration. Monitor for bruising and mucosal bleeding.

Components of yarrow modulate CYP450 metabolism (particularly CYP1A2, CYP2C9, and CYP3A4), potentially raising plasma concentrations of CYP3A4 substrates such as cyclosporine, erythromycin, and diazepam. Clinically relevant for narrow-therapeutic-index drugs.

Avoid yarrow in transplant recipients on cyclosporine/tacrolimus. For macrolides or benzodiazepines, monitor for toxicity (QT prolongation, sedation). Consider therapeutic drug monitoring when available.

Yarrow's diuretic action (mediated by bradykinin and prostaglandin-dependent pathways) can reduce renal lithium clearance and sodium excretion, leading to elevated lithium levels and potential toxicity (tremor, ataxia, confusion, seizures).

Avoid combination. If concurrent use is unavoidable, check lithium levels within 1 week, monitor renal function and sodium status, and watch for signs of lithium toxicity. Educate patients about hydration.

Yarrow's hexanic extract produces significant vasorelaxation via calcium channel blockade and nitric-oxide release, with leucodin and achillin identified as the major bioactive compounds. Combined with prescription antihypertensives this may cause additive hypotension.

Monitor blood pressure (supine and standing) during initiation. Warn patients about orthostatic dizziness. Consider dose adjustment of antihypertensives if symptomatic hypotension occurs.

Yarrow extract produced anxiolytic-like effects in rodent models partially blocked by the benzodiazepine antagonist flumazenil, suggesting weak GABA-A/benzodiazepine receptor modulation. Thujone in the essential oil is a GABA-gated chloride channel modulator. Combined with sedatives there is risk of additive CNS depression.

Counsel patients about enhanced drowsiness and impaired coordination. Avoid driving or operating machinery. Avoid combination with barbiturates and long-acting benzodiazepines in elderly patients (fall risk).

Hydroalcoholic extract of Achillea millefolium improved blood glucose, liver enzymes, and lipid profile comparably to metformin in streptozotocin-induced diabetic rats. Additive hypoglycemic effect possible when combined with antidiabetic therapy.

Monitor fasting glucose at initiation and during dose adjustments. Counsel patients on hypoglycemia signs. Anticipate possible small dose reductions in sulfonylureas or insulin with sustained yarrow use.