Levothyroxine (Synthroid) Medication

• Active ingredient: Levothyroxine
• Common brand names: Synthroid, Levoxyl, Levothroid
• Drug class: Thyroid hormone
• Pregnancy category: A
• Dosage forms: Tablets (0.025 mg, 0.05 mg, 0.075 mg, 0.088 mg, 0.1 mg, 0.112 mg, 0.125 mg, 0.137 mg, 0.15 mg, 0.175 mg, 0.2 mg, and 0.3 mg)

Synthroid (Levothyroxine T4) is a synthetic form of thyroxine (thyroid hormone). Levothyroxine is prescribed to replace natural thyroid hormones that are absent because of a disorder of the thyroid gland. It is slowly assimilated by body organs, so it usually takes up to six weeks before symptoms improve in adults.

Synthroid (Levothyroxine) Advantages & Benefits

• Safety and efficacy.
• Effective in different types of thyroid disorders.
• Less likely to cause allergic reactions than the natural thyroid products.
• In most cases synthetic T4 alone is enough to return TSH to the normal range.
• Ability to get a precise dose due to the different dosing available.
• Predictable effect because of standard hormonal content.
• Once a day dosing.
• Low cost.

Synthroid (Levothyroxine) Drawbacks

• May not supply sufficient T3 in some cases.
• Partial hair loss may occur rarely during the first few months of therapy, but it is usually temporary.
• High variability in the gastrointestinal absorption of T4.
• Variable potencies of different brands.

Time for Levothyroxine to clear out the system

Levothyroxine is eliminated slowly from the body with a half-life of approximately 7 days in a normal person.

How does Levothyroxine work?

The principal effect of thyroid hormones is to increase the metabolic rate of body tissues. The thyroid hormones are also concerned with growth and development of tissues in the young. The major thyroid hormones are L-thyroxine (T4) and L-triiodothyronine (T3). The amounts of T4 and T3 released from the normally functioning thyroid gland are regulated by the amount of thyrotropin (TSH) secreted from the anterior pituitary gland. T4 is the major component of normal thyroid gland secretions and is therefore the primary determinant of normal thyroid functions. T4 acts as a substrate for physiologic deiodination to T3 in the peripheral tissues. The physiologic effects of thyroid hormones are mediated at the cellular level primarily by T3. Levothyroxine provide T4 which upon absorption cannot be distinguished from T4 that is secreted endogenously.