Levothyroxine: What You Need to Know

Levothyroxine is the standard medicine for hypothyroidism. If your thyroid is underactive, this pill replaces the hormone your body lacks so you feel more energetic, think clearer, and keep your metabolism steady.

Wondering how fast it works? Most people notice subtle changes in 2–4 weeks and clearer improvement by 6–8 weeks. But labs and doses are what really guide treatment, not how you feel alone.

Dosage & Timing Tips

Take levothyroxine on an empty stomach, ideally first thing in the morning, 30–60 minutes before breakfast. That gives the best and most consistent absorption. If mornings don’t work, take it at bedtime at least 2 hours after your last meal.

Start low if you’re older or have heart disease. Younger, otherwise healthy adults often start at a replacement dose set by weight. Your doctor will check TSH and adjust every 6–8 weeks until levels settle into the target range.

Stick with the same brand or generic when possible. Switching brands can cause small changes in absorption, and those changes may prompt dose tweaks.

Common Interactions & Side Effects

Several things cut levothyroxine absorption: calcium, iron supplements, antacids with aluminum or magnesium, some cholesterol drugs (bile acid resins), and even soy or high-fiber meals. Wait 4 hours after taking levothyroxine before taking these, or take levothyroxine first and the others later.

Overdose or too-high dose can cause palpitations, shaking, sweating, weight loss, or anxiety. Too-low dose brings back fatigue, weight gain, and cold intolerance. If you notice symptoms changing, get your TSH checked and talk to your provider.

Pregnancy raises your thyroid needs. If you’re pregnant or planning pregnancy, tell your doctor—most women need a dose increase and closer monitoring to protect the baby and the mom.

Some people have trouble absorbing levothyroxine because of gut issues (like celiac disease or atrophic gastritis). If you don’t get better despite taking the pill correctly, ask your doctor about testing for absorption or trying an alternative formulation like a liquid or soft gel.

Missed dose? Take it as soon as you remember the same day. Don’t double up the next day. Keep a daily habit—same time, same routine—and set a phone alarm if you need to.

Before any new prescription or over-the-counter pill, mention levothyroxine. Even common drugs and supplements can require timing changes.

Want quick wins: take it consistently, space interacting supplements by several hours, check TSH at 6–8 week intervals after dose changes, and carry a list of your meds. That keeps your treatment steady and avoids surprises.

If you have chest pain, severe palpitations, or fainting after a dose change, get medical help right away. For other concerns, your primary care doctor or endocrinologist can adjust dose and testing to keep your thyroid under control.