L-Thyroxine Medication: Dosage & Side Effects

Instructor: Ian Lord

Ian has an MBA and is a real estate investor, former health professions educator, and Air Force veteran.

Levothyroxine is frequently prescribed for patients with hypothyroidism. In this lesson we will examine the dosages for different levels of severity and discuss the side effects of the medication.


Laura has been diagnosed by her doctor with hypothyroidism after testing revealed her thyroid isn't producing enough thyroid hormone. Without enough thyroid hormone, Laura is experiencing symptoms such as a lack of energy, hair loss, and increased cold-weather sensitivity.

Lack of energy is a symptom of hypothyroidism.
Tired Laura

Levothyroxine is the generic name for a common prescription medication for the treatment of hypothyroidism. It also known by the brand names Unithroid, Tirosint, Synthroid, Levo-T, Levothroid, and Levoxyl. Let's take a look at some of the different dosages and side effects that Laura's doctor will consider before prescribing levothyroxine.


Levothyroxine is typically administered as a tablet or capsule to be taken orally. The exact amount of Laura's dose will depend on the severity of her condition. Her doctor will most likely start her with a lower end of the dose range and then gradually step it up until her thyroid hormone levels return to normal.

For a mild form of hypothyroidism, the standard dosage range begins at 100-125 micrograms (mcg) per day. This can be stepped up to a maximum of 300 mcg per day. Patients over 50 years old or patients who are under 50 with cardiovascular disease start at 25-50 mcg per day and can have the dose adjusted 12.5-25 mcg every six to eight weeks. If the patient is over 50 and has cardiovascular disease begins even lower at 12.5-25 mcg per day, with 12.5-25 mcg increases made every four to six weeks as needed.

In more severe cases of hypothyroidism, the dosage starts at 12.5-25 mcg per day. The dosage is then increased by 25 mcg per day every two to four weeks as needed.

In some cases where thyroid hormone levels are normal but thyroid stimulating hormone has mildly increased, a small dose of levothyroxine may be administered. 1 mcg per kilogram of the patient's body weight may resolve the problem. The patient should be monitored annually to confirm thyroid hormone levels.

Laura will want to take the pill with a full glass of water on an empty stomach about 30 to 60 minutes before breakfast. If she cannot swallow a pill, it may be crushed up and mixed with 5-10 ml of water. She must prepare and consume the solution immediately; she shouldn't store the solution for later use. Since Laura is in her 30's and is otherwise healthy, her doctor started her on 100 mcg per day. That dosage seems to be working well for her and her doctor will continue to monitor her thyroid hormone levels on a regular basis.

Side Effects

Like all prescription medications, levothyroxine has the potential for side effects. If Laura experiences the two primary side effects at all, she should call her doctor or get emergency medical help. These are chest pain and a rapid or irregular heartbeat.

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