From the FDA Drug Label
The general aim of therapy is to normalize the serum TSH level Failure of the serum T4 to increase into the upper half of the normal range within 2 weeks of initiation of levothyroxine sodium therapy and/or of the serum TSH to decrease below 20 IU per litre within 4 weeks may indicate the patient is not receiving adequate therapy In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. Increase levothyroxine sodium dosage by 12.5 to 25 mcg per day. Monitor TSH every 4 weeks until a stable dose is reached and serum TSH is within normal trimester-specific range.
Increasing levothyroxine dosage is expected to decrease TSH levels. The goal of levothyroxine therapy is to normalize serum TSH levels, and adjustments to the dosage are made based on TSH levels. Monitoring of TSH levels is recommended after any change in dosage to ensure that the patient is receiving adequate therapy and to minimize the risk of overtreatment or undertreatment 1.
From the Research
Yes, increasing levothyroxine typically decreases TSH (thyroid-stimulating hormone) levels. Levothyroxine is a synthetic form of the thyroid hormone T4, which is prescribed to treat hypothyroidism. When you take levothyroxine, it increases the amount of thyroid hormone in your bloodstream. Through negative feedback, your pituitary gland senses these higher thyroid hormone levels and responds by reducing its production of TSH. This is exactly the intended effect when treating hypothyroidism, where the goal is to normalize thyroid hormone levels and bring TSH into the target range (typically between 0.5-2.5 mIU/L for most adults) 2.
Dose adjustments are usually made in small increments (often 12.5-25 mcg) with TSH rechecked after 6-8 weeks to allow the body to reach a new equilibrium. It's essential to monitor TSH levels closely, as increasing levothyroxine too much could lead to hyperthyroidism symptoms like rapid heart rate, anxiety, weight loss, and heat intolerance. Levothyroxine should be taken consistently, typically in the morning on an empty stomach, 30-60 minutes before eating, and separated from other medications that might interfere with its absorption.
Some studies have investigated the effects of altering levothyroxine doses on quality of life, mood, and cognition in L-T4 treated subjects. For instance, a study published in 2018 found that altering L-T4 doses in hypothyroid subjects to vary TSH levels in and near the reference range does not affect quality of life, mood, or cognition 3. However, the most recent and highest quality study on this topic is crucial for guiding clinical practice.
In the context of real-life clinical medicine, it is crucial to prioritize the patient's quality of life, morbidity, and mortality when adjusting levothyroxine doses. The goal is to achieve and maintain euthyroidism, minimizing the risk of under- or overtreatment. As noted in a 2022 study, optimal treatment of hypothyroidism requires a partnership between patient and physician, with vigilant appraisal of the patient's status and appropriate adjustment of their levothyroxine therapy 2.
Key considerations when adjusting levothyroxine doses include:
- Starting with a low dose (e.g., 25-50 μg) and gradually increasing as needed
- Monitoring TSH levels closely to avoid under- or overtreatment
- Adjusting doses in small increments (often 12.5-25 mcg) with TSH rechecked after 6-8 weeks
- Considering the patient's overall health, including any comorbidities or medications that may interact with levothyroxine
- Prioritizing the patient's quality of life, morbidity, and mortality when making treatment decisions.