What the FDA labels say about taking them together

Levothyroxine and rifampin

Levothyroxine's FDA label of February 20, 2024 names rifampin in its drug interactions section; the rifampin label PlainMeds reads does not name levothyroxine. The levothyroxine label: “Drug or Drug Class Effect Phenobarbital Rifampin Phenobarbital has been shown to reduce the response to thyroxine.”

Check it at the source: the levothyroxine FDA label on DailyMed (effective February 20, 2024, AbbVie Inc.); the rifampin FDA label on DailyMed (effective February 11, 2026, Lupin Pharmaceuticals, Inc.).

What does the levothyroxine label say about rifampin?

Levothyroxine label, drug interactions
Drug or Drug Class Effect Phenobarbital Rifampin Phenobarbital has been shown to reduce the response to thyroxine.

Levothyroxine Sodium label (Amneal Pharmaceuticals NY LLC, December 6, 2024), drug interactions
Drug or Drug Class: Carbamazepine Hydantoins Phenobarbital Rifampin; Effect: Stimulation of hepatic microsomal drug-metabolizing enzyme activity may cause increased hepatic degradation of levothyroxine, resulting in increased Ievothyroxine requirements. Phenytoin and carbamazepine reduce serum protein binding of levothyroxine, and total- and free-T 4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels and are clinically euthyroid.

Source: FDA drug label (Levothyroxine Sodium, NDA021210), Amneal Pharmaceuticals NY LLC, effective December 6, 2024 (SPL set fca88c97-5cd4-4834-ba87-deb5bd637788), via openFDA

Source: FDA drug label (Synthroid), AbbVie Inc., effective February 20, 2024 (SPL set 1e11ad30-1041-4520-10b0-8f9d30d30fcc), via openFDA; the full label on DailyMed

What does the rifampin label say about levothyroxine?

Rifampin's label (effective February 11, 2026) does not name levothyroxine in these sections. A label lists what its studies and reports found; it is not a complete list.

Source: FDA drug label (rifampin), Lupin Pharmaceuticals, Inc., effective February 11, 2026 (SPL set b56004f0-f23d-47f6-80c7-39884fccbccc), via openFDA; the full label on DailyMed

These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.

Both medicines on the record

36Levothyroxine generic labelers

13Rifampin generic labelers

	Levothyroxine	Rifampin
Labeled for	Hypothyroidism	n/a
Boxed warning	Yes	No
Pharmacy cost (NADAC)	$0.0588 per tablet 112 mcg tablet	$0.679 per capsule 300 mg capsule
Shortage now	No current entry	In shortage

Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)

What next?

Levothyroxine: the full record
Rifampin: the full record
Check more medicines together: up to five at once