Raloxifene with Levothyroxine Interaction Details
Brand Names Associated with Raloxifene
- Evista®
- Keoxifene
- Raloxifene
Brand Names Associated with Levothyroxine
- Levo-T®
- Levothroid®
- Levothyroxine
- Levoxyl®
- Synthroid®
- Tirosint®
- Unithroid®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Dec 26, 2023
Interaction Effect
Decreased levothyroxine efficacy
Interaction Summary
A case has been described of a 79-year old female in whom raloxifene caused malabsorption of levothyroxine. The patient had a subtotal thyroidectomy in 1970. With daily levothyroxine supplementation, her TSH levels remained normal for several years. She was prescribed raloxifene for osteopenia. Within 2 to 3 months, an elevated TSH level of 14.5 microunits/mL and symptoms of hypothyroidism led to an increase in levothyroxine sodium dosage from 0.15 mg to 0.2 mg/day. Over the next several months levothyroxine sodium was increased to 0.3 mg/day. Nine months after starting raloxifene she presented with a TSH of 9.36 microunits/mL. On 2 occasions separated by 4 weeks, T4 levels were obtained at 0, 30, 60, 90, 120, 180, 240, 300, and 360 minutes after ingestion of 1.0 mg levothyroxine sodium with and without the coadministration of 60 mg of raloxifene. Compared with levothyroxine alone, the results demonstrated lower levels of T4 at all study points following combined administration of levothyroxine and raloxifene. Further studies are needed to determine the effects of coadministration of raloxifene and levothyroxine.
Severity
Minor
Onset
Unspecified
Evidence
Probable
How To Manage Interaction
Administration of raloxifene may alter levothyroxine parameters and efficacy.
Mechanism Of Interaction
Unknown
Raloxifene Overview
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Raloxifene is used to prevent and treat osteoporosis (condition in which the bones become thin and weak and break easily) in postmenopausal (women who have experienced a change of life; end of menstrual periods) women. Raloxifene is also used to decrease the risk of developing invasive breast cancer (breast cancer that has spread outside of the milk ducts or lobules into the surrounding breast tissue) in postmenopausal women who are at high risk of developing this type of cancer or who have osteoporosis. Raloxifene cannot be used to treat invasive breast cancer or to prevent invasive breast cancer from coming back in women who have already had the condition. Raloxifene also cannot be used to decrease the risk of developing noninvasive breast cancer. Raloxifene should not be used in women who have not yet experienced menopause. Raloxifene is in a class of medications called selective estrogen receptor modulators (SERMs). Raloxifene prevents and treats osteoporosis by mimicking the effects of estrogen (a female hormone produced by the body) to increase the density (thickness) of bone. Raloxifene decreases the risk of developing invasive breast cancer by blocking the effects of estrogen on breast tissue. This may stop the development of tumors that need estrogen to grow.
Levothyroxine Overview
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Levothyroxine is used to treat hypothyroidism (condition where the thyroid gland does not produce enough thyroid hormone). It is also used with surgery and radioactive iodine therapy to treat thyroid cancer. Levothyroxine is in a class of medications called hormones. It works by replacing thyroid hormone that is normally produced by the body.
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Without thyroid hormone, your body cannot function properly, which may result in poor growth, slow speech, lack of energy, excessive tiredness, constipation, weight gain, hair loss, dry, thick skin, increased sensitivity to cold, joint and muscle pain, heavy or irregular menstrual periods, and depression. When taken correctly, levothyroxine reverses these symptoms.
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Definitions
Severity Categories
Contraindicated
These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.
Major
This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.
Moderate
This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.
Minor
While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.
Onset
Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.
Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.
Evidence
Level of documentation of the interaction.
Established: The interaction is documented and substantiated in peer-reviewed medical literature.
Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.
How To Manage The Interaction
Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.
It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.
Mechanism Of Interaction
The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.
Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.
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Information for our drug interactions is compiled from several drug compendia, including:
The prescribing information for each drug, as published on DailyMED, is also used.
Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.
The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.