Levothyroxine: What It Is, How It Works, and What You Need to Know

When your thyroid doesn’t make enough hormone, levothyroxine, a synthetic version of the thyroid hormone T4 used to treat hypothyroidism. Also known as Synthroid, it’s one of the most prescribed drugs in the world because it’s simple, effective, and works for most people. But taking it right matters more than you think. A wrong time, a cup of coffee, or even a calcium supplement can block your body from absorbing it — and leave you tired, sluggish, or still feeling unwell even if your dose seems right.

Levothyroxine isn’t like a painkiller you can take with breakfast. It needs a clean stomach, usually 30 to 60 minutes before food, to do its job. That’s why so many people switch to taking it at bedtime — if they can’t stick to the morning routine. And it’s not just food. Iron, antacids, soy, and even high-fiber meals can interfere. Your doctor checks your TSH levels, a blood marker that tells you how well your thyroid hormone replacement is working. If your TSH is too high, you’re underdosed. Too low, and you risk bone loss or heart problems. It’s a tight balance, and it takes time to get it right.

People on levothyroxine often don’t realize how many things can mess with it. That’s why some switch to newer formulations — like liquid or softgel versions — that absorb better with food. Others find that taking it with water, not juice or milk, makes a difference. And if you’re on other meds — like cholesterol drugs or antidepressants — you need to know about possible interactions. It’s not just about the pill. It’s about your whole routine.

Below, you’ll find real-world advice from people who’ve been there: how to time their dose around meals, what to do when they forget, how to spot signs it’s not working, and why some people still feel off even when their labs look fine. You’ll also see how levothyroxine compares to other thyroid treatments, what to ask your doctor, and how to avoid the most common mistakes that keep people from feeling better.