What are common drug interactions between ivermectin and prescription medications?
Executive summary
Most official drug references report few widely recognised interactions with ivermectin, but major regulators and drug monographs warn about interactions with blood thinners (anticoagulants) and P‑glycoprotein–related interactions (e.g., quinidine), and some resources flag a possible increase in warfarin effect; authoritative sources urge caution and monitoring [1] [2] [3]. Reporting varies: DermNet NZ states “no significant drug interactions are recognised” [1], while the FDA and Medscape explicitly cite interactions with blood thinners and P‑glycoprotein substrates [3] [2].
1. The official view: “no significant interactions” on one hand, regulator warnings on the other
DermNet New Zealand’s ivermectin entry — citing approved datasheets — says no significant drug interactions are recognised, reflecting product labels in some countries and long clinical experience for approved antiparasitic uses [1]. That statement sits alongside explicit FDA consumer guidance warning that “even doses of ivermectin for approved human uses can interact with other medications, like blood‑thinners,” showing regulatory caution despite generally benign interaction profiles at standard doses [3].
2. Blood thinners are the most consistently mentioned concern
Multiple sources single out anticoagulants as an interaction class. The FDA consumer update and mainstream reporting stress that ivermectin “can interact with blood thinners” and advise awareness when people take both drugs [3] [4]. Medscape’s drug monograph goes further, saying ivermectin “increases effects of warfarin by unspecified interaction mechanism,” which implies a clinically relevant potentiation that warrants monitoring of anticoagulation parameters [2].
3. P‑glycoprotein substrates and transporter effects: mechanism and examples
Drug interaction summaries note that drugs affecting P‑glycoprotein (the MDR1 transporter) can change ivermectin levels. Medscape notes that quinidine — a P‑glycoprotein inhibitor — will increase ivermectin levels, demonstrating a plausible pharmacokinetic pathway for interactions with other transporter inhibitors [2]. Sources indicate transporter-mediated changes are a mechanistic concern even if large‑scale clinical interaction data are limited [2].
4. Heterogeneous guidance reflects limited, context‑dependent evidence
The divergence between “no significant interactions” (DermNet NZ) and targeted warnings (FDA, Medscape) reflects two realities: (a) for routine, approved single‑dose antiparasitic use ivermectin has a favourable safety record, and (b) drug‑interaction risks rise when patients are on narrow‑therapeutic‑index drugs (like warfarin) or on medicines that alter ivermectin metabolism/transport [1] [2] [3]. Sources do not provide a comprehensive checklist of every interacting prescription drug; instead they highlight classes and illustrative examples [1] [2] [3].
5. Practical implications for clinicians and patients
Regulators and drug references imply practical steps: review anticoagulant therapy if prescribing or dispensing ivermectin, monitor INR or equivalent if on warfarin, and be cautious with drugs known to inhibit P‑glycoprotein (quinidine is one named example) because they can increase ivermectin exposure [3] [2]. DermNet’s “no significant interactions” note should not be read as an absolute clearance for unsupervised use, because national datasheets and FDA guidance still recommend vigilance for specific high‑risk combinations [1] [3].
6. Broader context: increased access, political pressure, and messaging risks
Legislative moves to expand OTC access and media attention on ivermectin mean more people may take it outside typical prescribing contexts; several news outlets and the FDA warn that easier access heightens the need for patient education about interactions — especially with blood thinners — and about differences between human and veterinary products [5] [6] [3]. This policy push may tilt the risk–benefit balance in real‑world settings where monitoring is limited [5] [6].
7. What the available sources do not say, and where uncertainty remains
Current reporting and monographs name anticoagulants and P‑glycoprotein interactions (quinidine example) but do not present a comprehensive list of every prescription drug that interacts with ivermectin; detailed interaction frequencies, magnitudes, and clinical outcome data are not provided in these sources (available sources do not mention a full exhaustive list). Large trials and systematic reviews cited focus on efficacy questions (e.g., for COVID‑19) rather than cataloguing interaction rates [7].
Bottom line: standard approved uses of ivermectin have a generally favourable safety profile, but regulators and drug monographs warn specifically about interactions with blood thinners (notably warfarin) and with drugs that affect P‑glycoprotein (quinidine as an example); clinicians should review concomitant anticoagulant therapy and transporter‑affecting drugs and monitor patients accordingly [3] [2] [1].