- The daily dosage of levothyroxine is dependent on age, sex (male or female) and weight.
- Other factors can affect how much levothyroxine you need, such as certain health conditions and other medications.
- Levothyroxine has a small therapeutic window, which means that the dose has to be tailored to the individual to avoid the consequences of over- or under-treatment.
- Levothyroxine has few side effects and is usually well tolerated.
- It takes several weeks for levothyroxine to build up in the body and for TSH levels to stabilize; symptoms may also take several weeks to resolve.
- At the start of treatment, it’s important to have TSH levels checked regularly (generally every 4 to 8 weeks or more often if required by your doctor) to make sure that the dose is correct and thyroid function has returned to normal.
- After TSH levels are stabilized, a TSH test should generally be done after 6 months and then every year or more often if required by your doctor, because factors like health, weight and age can affect dosing.
Staying on the same brand of levothyroxine
When it comes to hyperthyroidism medication, experts recommend that patients stay on the same levothyroxine preparation throughout treatment, which is usually for the remainder of their lives.
This is because different brands may be absorbed differently by your intestines, even in the same dose.
Because levothyroxine has a small therapeutic window, these differences in absorption could lead to over- or under-treatment which have unwanted consequences.
If a brand switch occurs, it is recommended that patients have their TSH levels checked, as they may need to have their hypothyroidism medication dose adjusted until their TSH levels have stabilized.
Risks of over- or under-treatment
Because levothyroxine has a small therapeutic window, finding the correct dose is important to avoid the consequences of over- or under-treatment. Essentially, overtreatment will result in hyperthyroidism whereas under-treatment will not resolve the symptoms of hypothyroidism.
Either way, the wrong dose can have effect on:
- Growth and development
- Heart function
- Bone health
- Ability to think
- Emotional state (your mood)
- Digestion and other functions of your stomach and intestines
- Metabolism of sugar and fats
If your dose of levothyroxine is too high, you may experience symptoms of hyperthyroidism. These can include:
- Chest pain or a fast or irregular heartbeat
- Nervousness and sweating
- Increased appetite
If you are experiencing these symptoms, contact your doctor. He or she may order a TSH test to determine if your TSH levels are too low. If this is the case, your dose of levothyroxine will likely be lowered.