5-alpha-reductase inhibitor (type II)
Finasteride with thyroid medication (levothyroxine)
Levothyroxine is one of the most prescribed medications worldwide, and many adults on it also use chronic medications such as Finasteride (Finasteride). The combination is generally safe, but levothyroxine's narrow therapeutic index and finicky absorption mean a few practical points matter more than for most other co-administered drugs at 1mg.
How Finasteride affects thyroid medication
Levothyroxine absorption is sensitive to timing relative to food, calcium, iron and several medications. Whether Finasteride interferes depends on Finasteride — most agents in 5-alpha-reductase inhibitor (type II) have no clinically meaningful effect on thyroid hormone levels, but a small number affect TSH or T4 free fraction. Finasteride binds with high affinity to 5-alpha-reductase type II, blocking the conversion of testosterone into DHT.
Practical timing
According to standard endocrine practice, levothyroxine is taken on an empty stomach at least 30 minutes before food and 4 hours from interacting medications. Finasteride at 1mg can usually be taken at any time relative to the levothyroxine dose, but the prescribing information for Finasteride should be checked for specific timing instructions.
Frequently asked questions
Will Finasteride affect my thyroid levels? ▾
Most 5-alpha-reductase inhibitor (type II) medications do not directly affect thyroid hormone levels at 1mg. Some affect TSH testing, hormone-binding proteins or T4 free fraction in subtle ways. Routine thyroid function tests every few months catch any meaningful drift.
When should I take Finasteride relative to levothyroxine? ▾
Levothyroxine is taken on an empty stomach with at least a 30-minute fast and 4-hour separation from interacting medications. Finasteride at 1mg usually has no specific timing constraint relative to levothyroxine; the pharmacist confirms based on the prescribing information for Finasteride.
Products containing Finasteride
More on Finasteride
- With alcoholFinasteride and alcohol — is it safe to drink?
- With foodShould Finasteride be taken with food?
- Side effectsFinasteride side effects: common, rare and warning signs
- Dosage guideFinasteride dosage guide: how much to take and when
- OnsetHow fast does Finasteride start working?
- DurationHow long does Finasteride last?
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