Does Levothyroxine Interact With Birth Control Pills?
In our latest question and answer, the pharmacist discusses whether or not levothyroxine (brand name Synthroid) interacts with birth control pills.
If I take Junel birth control and 25 mg levothyroxine at the same time every day will the levothyroxine impact the effectiveness of the birth control or vice versa?
Sep 20, 2022- Estrogen-containing birth control pills can affect how your body uses levothyroxine by increasing protein that binds thyroid hormone, potentially requiring a dose adjustment.
- Take levothyroxine at least 30 minutes before birth control pills or other medications to ensure proper absorption.
- If you've been taking levothyroxine and birth control pills together without problems, talk to your doctor before making any changes since consistency in how you take them matters most.
Answer
While there isn't a drug interaction between levothyroxine (brand name Synthroid) and birth control pills directly, if your birth control pills contain estrogen, it can potentially have a significant impact on your blood thyroid levels.
Estrogen Containing Birth Control Pills - Levothyroxine Interaction
Levothyroxine is a prescription thyroid medication indicated for the treatment of hypothyroidism or low thyroid levels. It doesn't directly interact with birth control pills, but as mentioned above, estrogen-containing birth control pills can affect thyroid levels which could possibly necessitate an alteration on your levothyroxine dose.
Estrogen has been shown in studies to increase thyroxine-binding globulin (TBG) concentrations in the blood. TBG is a transport protein that binds thyroid hormones (both T4 and T3) in the blood. Bound thyroid hormone is not active and could lead to symptoms of hypothyroidism including:
- Chills
- Lethargy
- Hair loss
- Lack of energy
The estrogen from birth control pills can potentially cause an increase in TBG. This increase can lead to more thyroid hormone being bound to it, making less available to be utilized in the body. This can in turn, lead to stimulation of thyroid-stimulating hormone (TSH), which activates when free thyroid concentration drops too low. This cascade of events can potentially alter the dosage needs of your prescription levothyroxine.
In summary, estrogen can cause the following:
- Increase in TBG
- Increase in bound thyroid hormone (to TBG)
- Decrease in free thyroid hormone
- Symptoms of hypothyroidism
- Stimulation of TSH
Separate Levothyroxine Administration From Other Drugs
Lastly, although there is no interaction between levothyroxine and birth control pills, they should not be administered at the same time to avoid decreases in the absorption of your levothyroxine dose. Levothyroxine should ideally be administered as follows:
- Take your dose of levothyroxine 30 minutes before food, drink or other medication. It should also be taken with at least 8 ounces (one cup) of water.
Having said all of the above, if you have been taking your birth control pills and levothyroxine together for some time, it may be prudent to stick with your current therapy and make no changes.
The most important aspect of levothyroxine dosing is to be consistent. Your thyroid levels may be normalized based on how you have been taking your levothyroxine and birth control pills. Before you make any changes to your current regimen, you should discuss it with your doctor.
References & sources
Glossary — Terms in This Answer
- Levothyroxine
- A prescription thyroid medication used to treat hypothyroidism or low thyroid levels.
- Hypothyroidism
- A condition where the thyroid gland does not produce enough thyroid hormone, resulting in low thyroid levels.
- Estrogen
- A hormone found in some birth control pills that can affect how thyroid hormones are transported in the blood.
- Thyroxine-binding globulin (TBG)
- A transport protein in the blood that binds and carries thyroid hormones, making them inactive.
- Thyroid hormones
- Chemical messengers produced by the thyroid gland, including T4 and T3, that regulate metabolism and energy in the body.
- Thyroid-stimulating hormone (TSH)
- A hormone that signals the thyroid gland to produce more thyroid hormone when free thyroid levels drop too low.
- Absorption
- The process by which a medication is taken up into the bloodstream from the digestive system.
- Lethargy
- A state of reduced energy and motivation, characterized by lack of enthusiasm and physical sluggishness.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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