What the FDA labels say about taking them together
Asparaginase and levothyroxine
Levothyroxine's FDA label of February 20, 2024 names asparaginase in its drug interactions section; the asparaginase label PlainMeds reads does not name levothyroxine. The levothyroxine label: “Androgens / Anabolic Steroids Asparaginase Glucocorticoids Slow-Release Nicotinic Acid These drugs may decrease serum TBG concentration.”
Check it at the source: the asparaginase FDA label on DailyMed (effective July 1, 2025); the levothyroxine FDA label on DailyMed (effective February 20, 2024, AbbVie Inc.).
What does the asparaginase label say about levothyroxine?
Asparaginase's label (effective July 1, 2025) 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 (Rylaze), Jazz Pharmaceuticals, Inc., effective July 1, 2025 (SPL set 857e53aa-1098-4dad-b654-0276cdd43e03), via openFDA; the full label on DailyMed
What does the levothyroxine label say about asparaginase?
Levothyroxine label, drug interactionsAndrogens / Anabolic Steroids Asparaginase Glucocorticoids Slow-Release Nicotinic Acid These drugs may decrease serum TBG concentration.
Levothyroxine Sodium label (Amneal Pharmaceuticals NY LLC, December 6, 2024), drug interactionsDrug or Drug Class: Clofibrate Estrogen-containing oral contraceptives Estrogens (oral) Heroin / Methadone 5-Fluorouracil Mitotane Tamoxifen; Effect: Androgens / Anabolic Steroids Asparaginase Glucocorticoids Slow-Release Nicotinic Acid
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
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
| Asparaginase | Levothyroxine | |
|---|---|---|
| Labeled for | Leukemia, lymphoma and myeloma | Hypothyroidism |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | n/a | $0.0588 per tablet 112 mcg tablet |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once