Synthroid vs. Tirosint

See how Synthroid and Tirosint compare on approved uses, dosing, side effects, and cost.

Key Takeaways

  • Synthroid and Tirosint are both synthetic levothyroxine (T4) used to treat hypothyroidism and to suppress TSH in thyroid cancer or nodules, just in different forms: tablet versus gel capsule.

  • Tirosint's gel-cap formula has fewer inactive ingredients, which may help patients with malabsorption, gastric bypass history, or sensitivities to fillers like lactose and dyes.

  • Neither drug is approved for weight loss, and taking more than the prescribed dose can cause serious heart and bone problems over time.

Synthroid vs. Tirosint Drug Summary

Synthroid

Synthroid is a synthetic thyroid hormone (levothyroxine sodium, T4) used to treat hypothyroidism and to suppress TSH in thyroid cancer or nodules. It is taken as a tablet once daily on an empty stomach, with the dose based on body weight and adjusted using periodic TSH testing.

Tirosint

Tirosint is also synthetic levothyroxine (T4), approved for the same hypothyroidism and TSH-suppression uses. It is taken as a liquid gel capsule once daily on an empty stomach, and its dose is likewise based on weight and adjusted using lab monitoring.

Synthroid vs. Tirosint Side Effects

Synthroid

Most common
Tremors (dose-related)
Palpitations (dose-related)
Insomnia (dose-related)
Headache (dose-related)

Tirosint

Most common
Tremors (dose-related)
Palpitations (dose-related)
Insomnia (dose-related)
Headache (dose-related)

Synthroid vs. Tirosint Dosage

Synthroid

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 12.5-25 mcg/day At the start
Maximum dose 1.6 mcg/kg/day If needed
Dose changes 2 increases As tolerated

Tirosint

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 12.5-25 mcg/day At the start
Maximum dose ~1.6 mcg/kg/day If needed
Dose changes 1 increase As tolerated

Synthroid vs. Tirosint Indications

Synthroid

Synthroid is FDA-approved to treat primary, secondary, and tertiary hypothyroidism by replacing the thyroid hormone the body is not making enough of. It is also used to suppress TSH in people with thyroid cancer or certain thyroid nodules and goiter. It carries a boxed warning against use for weight loss.

  • Primary hypothyroidism (underactive thyroid gland)

  • Secondary or tertiary hypothyroidism (pituitary/hypothalamic)

  • TSH suppression in thyroid cancer

  • TSH suppression for thyroid nodules or goiter

  • Not approved for obesity or weight loss (boxed warning)

Tirosint

Tirosint is FDA-approved for the same core uses as Synthroid: primary, secondary, and tertiary hypothyroidism, plus TSH suppression in thyroid cancer or nodules and goiter. It also carries a boxed warning against use for weight loss.

  • Primary hypothyroidism (underactive thyroid gland)

  • Secondary or tertiary hypothyroidism (pituitary/hypothalamic)

  • TSH suppression in thyroid cancer

  • TSH suppression for thyroid nodules or goiter

  • Not approved for obesity or weight loss (boxed warning)

Synthroid vs. Tirosint Pros and Cons

Synthroid

Synthroid is the most widely prescribed brand-name levothyroxine, with a long manufacturing track record and broad pharmacy availability. Its 12 tablet strengths allow for fine dose adjustments, though the tablet contains fillers some patients react to.

Pros

  • Widest range of tablet strengths (25 mcg to 300 mcg) for precise dosing

  • Long-standing manufacturing track record trusted by many prescribers

  • Stocked at nearly every pharmacy nationwide

  • Roughly $30 to $160 a month without insurance, before savings programs

Cons

  • Tablet may absorb less consistently in patients with GI malabsorption

  • Requires strict empty-stomach timing away from food and other drugs

  • Contains lactose and other fillers some patients react to

Tirosint

Tirosint is a gel-capsule levothyroxine built from only a handful of inactive ingredients. It is often chosen for patients with malabsorption or filler sensitivities, though it comes in fewer strengths and tends to cost more out of pocket.

Pros

  • Gel capsule has only four inactive ingredients, no dyes, gluten, or lactose

  • May absorb more consistently in malabsorption or gastric bypass patients

  • Easier to swallow for some patients than a tablet

  • Also available as Tirosint-SOL, a liquid for those who cannot swallow capsules

Cons

  • Fewer dosage strengths than Synthroid, making fine-tuning harder

  • Not stocked at every pharmacy, so refills may take extra time

  • Roughly $130 to $370 a month without insurance, before savings programs

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