When you take levothyroxine, a synthetic thyroid hormone used to treat hypothyroidism. Also known as Synthroid, it’s one of the most prescribed drugs in the world—but it doesn’t play well with everything. If you’re taking it and still feel tired, gain weight, or have brain fog, the problem might not be your dose. It could be what you’re taking with it.
Calcium supplements, commonly used for bone health, can block levothyroxine from being absorbed. Same with iron supplements, often taken for anemia or during pregnancy. Even coffee, soy milk, and antacids like Tums can get in the way. It’s not magic—it’s chemistry. Levothyroxine needs an empty stomach and at least 30 to 60 minutes before anything else to work right. Take it first thing in the morning, wait, then eat or take other meds. If you’re on multiple pills, talk to your pharmacist about timing. A simple change like this can make your thyroid levels stable again.
Some heart meds, like cholestyramine, a cholesterol-lowering resin, are notorious for binding to levothyroxine in the gut. So are certain antibiotics and seizure drugs. Even some herbal products, like St. John’s wort, can speed up how fast your body breaks it down. You don’t need to stop your other meds—just space them out. Most doctors recommend taking levothyroxine at least four hours before or after these substances. And if you’re switching brands or generics, get your TSH checked. Not all formulations are the same.
There’s no one-size-fits-all fix, but knowing the big offenders gives you control. You’re not just taking a pill—you’re managing a system. The posts below break down real cases: how people fixed their levothyroxine interaction issues, what worked when nothing else did, and which supplements are safe to take alongside thyroid meds. You’ll find clear, no-fluff advice from people who’ve been there—and the science behind why timing matters more than you think.
