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23rd May 2025
Drug interactions with thyroid hormone replacement therapy
Thyroid hormone tablets taken orally require acidity for dissolution prior absorption, and therefore should be taken prior to eating or taking other medications. Around 60-80% of levothyroxine is absorbed 2-4 hours after ingestion in a fasting state.
| Medications | Type of interaction | Recommended action |
|---|---|---|
| PPI (proton pump inhibitors) | Decrease levothyroxine absorption | Increase levothyroxine dose or switching to a liquid preparation. |
| Ferrous sulphate, calcium carbonate, aluminium hydroxide, raloxifene and sucralfate | Decrease thyroid hormone absorption | Ingestion of thyroid hormone 4 hours before taking these medications or taking levothyroxine at bedtime. |
| bile acid sequestrants e.g., cholestyramine and colestipol | Decrease thyroid hormone absorption | Patients are advised to take levothyroxine 1 hour before or 4-6 hours after taking these medications. |
| Soy formula, milk, and coffee | Impair levothyroxine absorption. | Advised to be taken on empty stomach. |
| Rifampicin, phenytoin, phenobarbital, carbamazepine, imatinib | Increase thyroxine clearance. | Levothyroxine dose requirement should be increased.
TFTs are monitored and dose adjusted accordingly. |
| Anticancer drugs e.g., imatinib | Decrease levothyroxine plasma concentration | |
| Antidepressants | Sertraline decreases levothyroxine effectiveness.
Response to tricyclics are accelerated precipitating to cardiac arrhythmias. |
|
| B-blockers e.g., propranolol | Decrease peripheral conversion of levothyroxine to triiodothyronine.
Levothyroxine increases propranolol metabolism. |
|
| Sex hormones | Oestrogens (e.g., in COCs) increase serum thyroxine-binding globulin.
Androgens decrease serum thyroxine binding globulin. |
Regular TFTs monitoring
Increase thyroxine dose with oestrogens and decrease with androgen therapy. |
Table 8: Drug interactions with thyroid hormone replacement therapy overview:
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