From the Guidelines
Prednisone can affect levothyroxine absorption and thyroid function tests, potentially requiring dose adjustments, as evidenced by the lack of direct evidence on the benefits and harms of screening for thyroid dysfunction in nonpregnant, asymptomatic adults 1. When taking prednisone, you may need to monitor your thyroid levels more closely as corticosteroids can decrease TSH levels and alter T4 to T3 conversion. The following key points should be considered:
- If you're on both medications, take levothyroxine at least 4 hours apart from prednisone to minimize interaction.
- For patients on stable levothyroxine therapy who need to start prednisone, thyroid function tests should be checked 4-6 weeks after beginning corticosteroid treatment.
- The impact varies based on prednisone dose and duration—higher doses (>20mg daily) and longer courses have more significant effects.
- Prednisone can mask symptoms of hypothyroidism and create a false impression of adequate thyroid replacement.
- If you experience unusual fatigue, weight changes, or other thyroid-related symptoms while taking both medications, contact your healthcare provider for evaluation. The physiological basis for this interaction involves prednisone's effects on the hypothalamic-pituitary-thyroid axis and peripheral thyroid hormone metabolism, which can complicate management of thyroid conditions. It is essential to note that the USPSTF found no direct evidence that treatment of thyroid dysfunction based on risk level alters final health outcomes, and long-term randomized, blinded, controlled trials of screening for thyroid dysfunction would provide the most direct evidence on any potential benefits of this widespread practice 1.
From the FDA Drug Label
Metabolic clearance of corticosteroids is decreased in hypothyroid patients and increased in hyperthyroid patients. Changes in thyroid status of the patient may necessitate adjustment in dosage
The effect of Prednisone on Levothyroxine (T4) levels and Thyroid Hormone Levels is not directly stated in terms of increase or decrease. However, it is mentioned that changes in thyroid status may necessitate adjustment in dosage of corticosteroids, implying an interaction between corticosteroid therapy and thyroid hormone levels.
- Key Point: The relationship between prednisone and thyroid hormone levels is related to the metabolic clearance of corticosteroids, which is affected by the patient's thyroid status 2.
From the Research
Effect of Prednisone on Levothyroxine (T4) Levels and Thyroid Hormone Levels
- The effect of prednisone on serum thyrotropin (TSH), thyroxine (T4), and triiodothyronine (T3) concentrations was investigated in several studies 3, 4.
- A study found that prednisone therapy causes a significant decrease of total T3 concentration together with a considerable rise of reverse T3 and lower T3-binding capacity in children 3.
- In hypothyroid patients, orally administered prednisone resulted in a significant decrease in mean serum TSH levels without significant changes in levels of serum T4, T3, and thyroxine binding globulin (TBG) 4.
- Another study suggested that T3 measurement does not add anything to the interpretation of thyroid hormone levels in subjects with hypothyroidism on levothyroxine replacement therapy 5.
- The use of prednisone and its effect on TSH, T4, and T3 levels can be complex and may require careful consideration of individual patient factors, as changes in TSH within the reference range may provoke symptoms in some sensitive patients 6.
Key Findings
- Prednisone therapy can decrease total T3 concentration and increase reverse T3 levels 3.
- Prednisone can decrease mean serum TSH levels without significant changes in serum T4, T3, and TBG levels 4.
- T3 measurement may not be informative in assessing levothyroxine over-replacement in hypothyroid patients 5.
- Changes in TSH reference ranges can impact levothyroxine prescribing and laboratory test use 7.
Studies on Prednisone and Thyroid Hormone Levels
- A 1985 study examined the effect of prednisone therapy on serum levels of T4, T3, reverse T3, TBC, basal TSH, and TSH response to TRH in children 3.
- A 1978 study investigated the effect of exogenous prednisone on serum TSH, T4, and T3 concentrations in hypothyroid patients 4.
- A 2015 study found that T3 measurement does not add anything to the interpretation of thyroid hormone levels in subjects with hypothyroidism on levothyroxine replacement therapy 5.
- A 2020 study evaluated the population-level change in levothyroxine prescribing and TSH testing after a minor planned decrease in the upper limit of the reference range for TSH 7.