Levothyroxine — what it does and why you might need it
Levothyroxine is a synthetic thyroid hormone doctors give when your body doesn’t make enough natural thyroid hormone. If you feel tired, gain weight, or get cold easily, your doctor may test your TSH and suggest levothyroxine. The drug replaces missing hormone and helps energy, metabolism, and brain function return to normal. It works well when used the right way, but small details matter — timing, interactions, and testing change how well it helps you.
How to take levothyroxine
Take levothyroxine on an empty stomach, ideally 30 to 60 minutes before breakfast. Food, coffee, and supplements can cut how much your body absorbs. If morning doses don't fit your routine, take it at least 3–4 hours after your last meal before bed — but keep the timing consistent every day.
Use the same brand or formulation unless your doctor says otherwise. Different brands or generic versions can absorb differently, so switching without guidance can change your hormone levels. If your doctor switches your prescription, expect a repeat TSH test in 6–8 weeks.
Missed a dose? Take it as soon as you remember that day. Don’t double up the next day.
Side effects, interactions & testing
When dosed correctly, levothyroxine usually causes few side effects. Symptoms of too much hormone include racing heart, shakiness, sweating, and insomnia. Too little and you’ll still feel sluggish or cold. If you notice new heart symptoms, contact your doctor — especially if you have heart disease.
Common interactions lower levothyroxine absorption: calcium, iron, antacids with aluminum or magnesium, bile acid binders, sucralfate, and some cholesterol drugs. Soy, high-fiber meals, and certain herbal supplements can interfere too. Take these at least 4 hours apart from your thyroid pill.
Medications like warfarin and certain diabetes drugs may need dose checks when you start or change levothyroxine. Tell every provider you see that you take it.
Monitoring is simple but crucial. Your doctor will check TSH (sometimes free T4) about 6–8 weeks after starting or changing dose, then less often once stable — usually every 6–12 months or during pregnancy. Pregnant people need closer checks because requirements often rise.
Storage and safety: keep tablets in a dry place at room temperature, away from sunlight. Don’t cut or crush extended-release forms unless the label allows it. Store out of reach of children and pets.
Practical tips: keep a pill box or phone reminder to keep timing steady; list all supplements and meds for your doctor; bring a medication label to appointments so your provider knows the exact product. If you have persistent symptoms despite a normal TSH, ask about absorption checks, adherence, or other health issues that mimic hypothyroidism.
Levothyroxine is a low-risk, high-benefit drug when used correctly. Small habits — timing, consistent brand, and routine testing — make a big difference in how well it works for you.
