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Levothyroxine: What to expect day 1, week 1, month 1 and beyond

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When you’re diagnosed with hypothyroidism, you’ll likely be prescribed levothyroxine. Learn how it works to control your condition and when your symptoms will improve.
Written by Jessica Migala
Updated on July 11, 2022

Your thyroid plays an essential role in your metabolism. The butterfly-shaped gland at the base of your neck makes hormones that affect your heart, muscle and digestive function. And it even regulates your body temperature.

When your thyroid doesn’t make enough of these hormones, it’s called hypothyroidism. And the consequences can range from mild to severe. Symptoms of hypothyroidism can include feeling cold, constipation, fatigue, weight gain, and dry skin and hair. It can also lead to mental health issues, heart problems and fertility troubles.

The gold-standard treatment for diagnosed hypothyroidism is levothyroxine (Synthroid®, Levoxyl®). It’s a synthetic hormone, explains Philip K. King, PharmD. King is an assistant professor of pharmacy practice at Butler University College of Pharmacy and Health Sciences in Indianapolis. “That means it’s designed to walk and talk just like the thyroid hormone that’s created in your body. It’s chemically identical,” King explains.

The medication gives your body more of the hormone thyroxine (T4). When taken in proper doses, it will help bring your thyroid hormone levels back to normal.

Several medications can affect the absorption of levothyroxine and reduce its effects, says Kristy L. Brittain, PharmD. Brittain is an associate professor at the Medical University of South Carolina College of Pharmacy. So make sure your doctor and pharmacist know about all the medications and over-the-counter supplements you’re taking. (Using the same pharmacy for all your medications can help, too.)

Wondering what to expect if you’ve been given a levothyroxine prescription? Here’s what you need to know. (And don’t forget to bring this free prescription discount card with you to the pharmacy. It could save you up to 80% on your medications.)

Day 1

It’s helpful to understand what happens in the body after you take levothyroxine. Once the medication enters your bloodstream, the T4 hormone is converted into T3 (triiodothyronine). This is the “active” form of the hormone that does the work, says King.

This medication can be finicky, though. “There are a lot of things that alter the absorption of levothyroxine,” says Brittain.

You’ll want to take it first thing in the morning with a full glass of water on an empty stomach. Then wait 30 to 60 minutes before eating or drinking anything else. (Yes, that includes coffee.) Otherwise, your body won’t receive most of the thyroid hormone from the medication.

Calcium and iron can bind to levothyroxine and carry it out of the body before it’s had a chance to do any work, says Brittain. And that’s true whether the minerals are in food or in a supplement. Aim to take supplements at least 4 hours after levothyroxine, she says. And it’s best to avoid eating calcium-rich foods such as yogurt or milk for breakfast.

Antacids that contain calcium carbonate, aluminum or magnesium can also affect absorption.

Days 3 to 5

During these days, blood levels of thyroid hormone will start to rise, says Brittain. That will begin to trigger your metabolism to work at a more normal pace.

That said, you won’t feel different yet, adds King. Other changes can include more stable blood sugar, improved body temperature regulation and a less sluggish digestive system.

Here are the most common side effects people notice when they take levothyroxine. If you notice any of these symptoms, talk to your doctor. They’ll likely want to know if these issues pass with time or worsen.

  • Irregular heartbeats
  • Shortness of breath
  • Muscle cramps, pain or weakness
  • Increased appetite
  • Feeling hot
  • Feeling depressed or irritable
  • Diarrhea

Weeks 1 through 3

Start monitoring your symptoms. “In most situations, symptoms will not change for 2 to 3 weeks,” says King. “That’s important to know, because you might not feel much different for a while,” he says.

If you notice rapid improvement within 1 week, it’s possible that you’ve been prescribed too high of a dose. Taking too much levothyroxine can tip you into hyperthyroidism (an overactive thyroid). And this comes with a new set of symptoms. “Early improvement of symptoms isn’t necessarily a good sign,” says King.

Recommended reading: Could your depression be linked to your thyroid?

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Weeks 4 to 6

This is when you can expect peak effects to hit, says Brittain. That means you’ll likely feel improvement in your symptoms. That said, some people don’t have any symptoms when they have a borderline underactive thyroid. So medication may not impact how you feel, she adds.

In general, the 4- to 6-week mark is when your provider will want to repeat bloodwork to check thyroid levels. Your dosing may need an adjustment to get it right, says Brittain. If you started on levothyroxine, your doctor likely won’t switch you to a brand-name medication.

“This is one drug that we recommend patients stay on long term, as there can be minor differences between the different products,” says Brittain. “Different formulations may affect absorption.” Keeping it consistent will help your health care team better track your thyroid function.

Be sure to search for your prescription on the Optum Perks discount app before heading to the pharmacy. You could find medication coupons for up to 80% off.

Your doctor will continue to recheck until your thyroid hormones are back to normal. And be sure to keep them up to date on changes to your morning routine — giving up coffee or adding yogurt back into breakfast, for example. This way they can monitor your levels more closely and adjust your dose as needed.

Having a hard time following the rules of levothyroxine? King notes that you might be able to take it at night as long as it’s 3 to 4 hours after your last meal or snack. That’s when your stomach will be empty again. But you’ll still have to take it with a full glass of water (and that can send you to the bathroom in the middle of the night).

So weigh the option that’s best for you, and as always, talk to your doctor before making that type of change.