Levothyroxine: What You Need to Know

Millions of people take levothyroxine to replace missing thyroid hormone. If you’ve been diagnosed with hypothyroidism, had a thyroid removed, or need hormone support during pregnancy, this drug is often the standard prescription. It’s simple in concept—replace the hormone your body can’t make—but small details make a big difference for how well it works.

How levothyroxine works and who needs it

Levothyroxine is a synthetic form of thyroxine (T4). Your body turns T4 into the active hormone T3 as needed. Doctors prescribe it when the thyroid underproduces hormone, or after surgery or radioiodine treatment. The goal is to get your TSH into the target range so you feel normal—less fatigue, better mood, stable weight, and more energy.

How to take it — timing and basics

Take levothyroxine once a day on an empty stomach, ideally 30–60 minutes before breakfast. Consistency matters: take it the same way every day. Avoid coffee, calcium, iron supplements, antacids, and some soy products within four hours of the pill — they cut absorption and can change your blood levels.

Don’t swap brands or switch from brand-name to generic without checking your TSH. Small formulation differences can change how your body absorbs the drug. If a change is unavoidable, plan a TSH test 6–8 weeks after the switch.

Typical starting doses depend on age, heart health, and how low your thyroid function is. Older adults or people with heart disease often start low and rise slowly. Younger, healthy adults may start at a full replacement dose. Your doctor adjusts the dose based on TSH and symptoms every 6–12 weeks until stable.

Pregnancy usually requires a higher dose because your body needs more thyroid hormone. If you’re pregnant or trying to conceive, work with your provider—untreated hypothyroidism raises risks for you and the baby.

Watch for signs your dose isn’t right. If you feel tired, cold, constipated, or gain weight, you may be undertreated. If you’re jittery, losing weight, having palpitations, or trouble sleeping, you could be taking too much. Report these symptoms and get labs—don’t adjust the pill yourself.

Buying levothyroxine online? Only use pharmacies that require a prescription, show clear contact info, and have verified credentials. Avoid sites offering the drug without a prescription or at suspiciously low prices. Keep your doctor in the loop: they’ll need to monitor TSH and manage dose changes.

Storage is simple: keep the tablets in a cool, dry place away from sunlight. Most are stable at room temperature. If you miss a dose, take it as soon as you remember the same day; don’t double up the next day.

Levothyroxine is a highly effective, long-term therapy when taken correctly. Small routine checks and consistent habits make it work well—so focus on timing, interactions, and follow-up labs, and you’ll get the benefits without surprises.