Thyroid Medication Dosing: What You Need to Know About Dosage, Timing, and Adjustments

When you take thyroid medication, a synthetic hormone used to replace or supplement the thyroid hormone your body isn’t making enough of. Also known as thyroid hormone replacement, it’s one of the most common prescriptions in the U.S.—but getting the dose wrong can leave you tired, gaining weight, or feeling anxious for no reason. It’s not just about popping a pill. The right thyroid medication dosing depends on your age, weight, other health conditions, and how your body responds over time.

Most people start with levothyroxine, the standard synthetic form of T4, the main hormone produced by the thyroid gland. Also known as Synthroid or generic equivalents, it’s taken once daily on an empty stomach, usually in the morning, at least 30 to 60 minutes before eating. Skipping this step—like taking it with coffee, calcium, or iron—can slash absorption by half. That’s why two people on the same dose can feel totally different. Your doctor doesn’t just pick a number out of thin air. They look at your TSH levels, the thyroid-stimulating hormone from your pituitary gland that tells your thyroid how much hormone to make. Also known as thyroid function test, it’s the most reliable marker for adjusting your dose. A high TSH means you’re under-dosed. A low TSH means you’re over-dosed. But here’s the catch: some people feel better at a TSH of 2.5, others need it at 1.0. Your symptoms matter just as much as the lab number.

Age, heart health, and other meds change everything. Older adults often need lower doses. People with heart disease can’t handle sudden spikes in thyroid hormone. And if you’re on iron, antacids, or even soy supplements, they can block absorption. Even switching brands—even if they’re both generic—can shift your levels. That’s why most doctors test your TSH every 6 to 8 weeks after a dose change, then once a year once you’re stable.

Thyroid medication isn’t a set-it-and-forget-it kind of thing. Weight gain? Fatigue? Brain fog? It might not be your lifestyle—it might be your dose. And if you’ve been on the same dose for years without a checkup, you’re flying blind. The posts below cover real cases: how one person fixed their energy after years of being told "it’s just stress," how timing the pill 3 hours after breakfast made all the difference, and why some patients need a combo of T4 and T3. You’ll see what works, what doesn’t, and what your doctor might not tell you unless you ask.