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
Tirosint
Synthroid vs. Tirosint Dosage
Synthroid
Tirosint
| 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 |
| 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
| 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
| 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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