Carnitine (L-carnitine and acetyl-L-carnitine) has 7 documented interactions in Magellan’s curated dataset, covering Anticoagulants (blood thinners), Antiplatelet drugs, Anti-seizure medications, Chemotherapy and cancer therapy, Thyroid medication (levothyroxine), Antibiotics. Each entry below gives the mechanism as the cited reference states it, the direction the risk runs, how serious that reference treats it, and what to actually do about it — which is, in every case, a conversation with the clinician or pharmacist who manages the prescription rather than a decision you make alone.
What it is. L-carnitine is a naturally occurring, vitamin-like compound synthesized from the amino acids lysine and methionine and also obtained from the diet, mainly red meat. Its central physiological role is to shuttle long-chain fatty acids across the inner mitochondrial membrane so they can undergo beta-oxidation, the process that supplies most of the heart's energy.
Where it sits on the evidence. Magellan grades the supplement itself as Moderate evidence, with a typical studied dose of ~2 g/day; analyses show no clear added benefit above ~3 g/day. That grade is about whether it works, not about whether it is safe alongside your medication — the two questions are independent, and this page answers only the second.
Products this covers: Acetyl-L-Carnitine (ALCAR) · L-Carnitine.
How the risks cluster. The entries split across 5 different mechanisms — additive; nutrient level; may make a side effect of the treatment worse rather than better, on the cited trial evidence.; opposing; bleeding risk — and they are not managed the same way, so read each one rather than assuming a single rule covers all of them.
Safety and efficacy are separate questions, and this page only answers the first. For the second, the study Magellan’s coverage of Carnitine rests on is:
“L-carnitine is associated with a 27% reduction in all-cause mortality, a 65% reduction in ventricular arrhythmias, and a 40% reduction in anginal symptoms in patients experiencing acute myocardial infarction”
A strong result does not make a supplement safe alongside your prescription, and a documented interaction does not mean the supplement does not work. Magellan grades those two things separately, and neither grade moves for a commission.
Magellan’s Medication Safety Check runs entirely on your device — type the medicines you take and it flags every documented interaction in this dataset. Nothing you type is sent anywhere.
Open the Medication Safety Check →Carnitine/acetyl-L-carnitine may have additive anticoagulant effects; a published case report documented potentiation of the oral anticoagulant acenocoumarol by L-carnitine supplementation, and warfarin is listed as a drug that usually should not be combined with levocarnitine without dose adjustment and monitoring.
Medicines in this group include: Warfarin (Coumadin, Jantoven), Apixaban (Eliquis), Rivaroxaban (Xarelto), Dabigatran (Pradaxa), Edoxaban (Savaysa), Heparin (Lovenox, Enoxaparin), Acenocoumarol (Sintrom), Aspirin (Asa, Bayer aspirin) and 4 more.
These anticonvulsants reduce blood carnitine levels; valproic acid in particular can cause carnitine-related hepatotoxicity/hyperammonemia, and IV L-carnitine is sometimes used clinically to treat valproate toxicity.
Medicines in this group include: Phenytoin (Dilantin), Carbamazepine (Tegretol), Valproic acid (Depakote, Valproate), Phenobarbital (Luminal), Levetiracetam (Keppra), Lamotrigine (Lamictal), Gabapentin (Neurontin), Topiramate (Topamax).
In clinical trials, acetyl-L-carnitine actually worsened chemotherapy-induced peripheral neuropathy, with the adverse effect persisting at 2-year follow-up; it is not recommended for patients undergoing chemotherapy for neuropathy prevention.
Medicines in this group include: Methotrexate (Trexall, Otrexup), Tamoxifen (Nolvadex), Cisplatin, Doxorubicin (Adriamycin), Vincristine (Oncovin), Bortezomib (Velcade), Cyclophosphamide (Cytoxan).
L-carnitine acts as a peripheral antagonist of thyroid hormone action and may decrease how well thyroid hormone medication works.
Medicines in this group include: Levothyroxine (Synthroid, Levoxyl), Liothyronine (Cytomel), Desiccated thyroid (Armour thyroid, Np thyroid).
L-carnitine may increase the anticoagulant effect of warfarin/acenocoumarol, raising bruising and bleeding risk; more frequent INR monitoring and possible dose adjustment are recommended.
Medicines in this group include: Warfarin (Coumadin, Jantoven), Apixaban (Eliquis), Rivaroxaban (Xarelto), Dabigatran (Pradaxa), Edoxaban (Savaysa), Heparin (Lovenox, Enoxaparin), Acenocoumarol (Sintrom).
Chronic use of these antibiotics can deplete tissue carnitine levels, though no clear cases of resulting illness have been documented.
Medicines in this group include: Ciprofloxacin (Cipro), Levofloxacin (Levaquin), Moxifloxacin (Avelox), Doxycycline (Vibramycin), Minocycline (Minocin), Tetracycline (Sumycin), Cephalexin (Keflex), Cefdinir (Omnicef) and 3 more.
L-carnitine (and acetyl-L-carnitine) can act as a peripheral antagonist of thyroid hormone action, which could theoretically blunt the effectiveness of thyroid medication.
Medicines in this group include: Levothyroxine (Synthroid, Levoxyl), Liothyronine (Cytomel), Desiccated thyroid (Armour thyroid, Np thyroid).
These are the warning signs that go with the medication classes on this page. They are general safety-netting, not a prediction that any supplement will cause them.
If something feels seriously wrong, do not wait for an appointment. Call 911 (US) or your local emergency number.
Severity describes the interaction as the cited reference frames it, not how a specific person will react. A “minor” entry in someone with kidney disease, on five other drugs, can matter more than a “major” one in someone on nothing else.
This is a curated set of interactions with citations — not an exhaustive pharmacology database. An interaction that is absent here has not been ruled out; it may simply not be documented in the references Magellan curates from. Supplements are also not batch-tested for identity or contamination the way prescription drugs are, so what is on the label is a claim rather than a guarantee. And most of these entries come from case reports and mechanistic work rather than randomized trials, which is exactly why the sensible response is a pharmacist review rather than either alarm or dismissal.
22 documented interactions across 17 supplements.
43 documented interactions across 24 supplements.
9 documented interactions across 9 supplements.
8 documented interactions · shares a drug class with Carnitine.
3 documented interactions · shares a drug class with Carnitine.
3 documented interactions · shares a drug class with Carnitine.
4 documented interactions · shares a drug class with Carnitine.
The mechanism and the research behind the compound itself.
A–Z of every supplement and drug class in this dataset, plus how to read an interaction.
What the research actually shows, graded independently of affiliate commissions.
Not without checking with the prescriber or pharmacist first. Magellan's dataset grades this as a moderate interaction: Carnitine/acetyl-L-carnitine may have additive anticoagulant effects; a published case report documented potentiation of the oral anticoagulant acenocoumarol by L-carnitine supplementation, and warfarin is listed as a drug that usually should not be combined with levocarnitine without dose adjustment and monitoring. (Source: Carnitine | Memorial Sloan Kettering Cancer Center.)
7 interactions are documented in Magellan's curated dataset: 5 moderate, 2 minor. They cover Anticoagulants (blood thinners), Antiplatelet drugs, Anti-seizure medications, Chemotherapy and cancer therapy, Thyroid medication (levothyroxine). Absence from this list is not proof of safety — it means no interaction is documented in the references we curate from.
Magellan lists the typical studied dose as: ~2 g/day; analyses show no clear added benefit above ~3 g/day. Dose matters for interactions — several of the entries on this page describe effects that only appear at supplemental rather than dietary intakes.