Synthroid is a prescription medication that is a replacement for a natural hormone in the body. It comes with its own precautions, indications, and side effects. Synthroid is a brand name for the medication levothyroxine.

Many hormones are made by various organs of the body. The thyroid is an important hormone that helps to regulate the metabolism and energy of the body. Synthroid is used to treat people with a low amount of thyroid hormone, also known as hypothyroidism. When the thyroid is underactive, it isn’t producing enough thyroid hormone, which can have many different effects on the body. This medication is also used when a patient needs radioiodine therapy and surgery to treat a specific type of cancer called well-differentiated thyroid cancer.

How Does It Work?

When there isn’t enough thyroid hormone being produced, or any at all, this medication replaces the missing hormone. Usually, the thyroid gland releases this hormone, but some patients have a problem with this gland. It could be injured because of certain medications or surgery, or it could have been completely removed. It can also happen naturally.

When you don’t have enough of this hormone in the body, it can cause problems with energy and mental activity as well as fertility. It can cause weight gain, dry skin, fatigue, slow speech, depression, hair loss, and difficult or irregular menstruation. When children don’t have enough thyroid hormone, it can affect their physical and mental development. Taking Synthroid as prescribed can reverse all of these problems.

Synthroid is a synthetic substance identical to the naturally occurring hormone T4. It can be used to completely replace this hormone if the body doesn’t make any or add to the amount that is naturally produced in the body.


This medication is available in generic form. However, patients aren’t supposed to switch between the generic medicines and Synthroid. Each of these may have varying effects on hormone levels. The American Thyroid Association recommends that patients not switch between these medications. If you start on Synthroid, you should stay on it as long as you need more thyroid hormone.

What Forms Are Available?

There are a couple of forms of this medication that are taken by different patients for different reasons.

Oral Medication

Synthroid is available in oral tablet and capsule form. It comes in a wide range of dosages so that patients can get precisely what they need. Always take the tablets or caplets in the manner indicated by the doctor and the packaging.


It can also be made available as an infusion or injection for those who aren’t able to take pills.

Precautions and Warnings

Sometimes, not having enough thyroid hormone can cause weight issues. When this happens, this can be helped by taking Synthroid. However, if the weight problem isn’t caused by too little thyroid hormone, patients are warned not to take this medication just for weight loss. If there isn’t a thyroid problem behind the extra weight, Synthroid will not work to help patients lose weight. There’s also a black-box warning on this medication that warns against taking it for weight loss and taking it with anything that causes weight loss such as amphetamines. There are various medications prescribed for weight loss, and none of these can be taken with Synthroid. Never take more than you are prescribed in the hope that it will help you lose weight. This can cause serious side effects like seizures, coma, confusion, and can even be fatal. Always take it exactly as prescribed and as often as prescribed.

There are a number of health conditions that may mean you aren’t able to take this medication. These include certain heart conditions like atrial fibrillation. If you’re diabetic, this medication may cause you to have higher blood sugar. If you have adrenal gland problems, this medication can cause your adrenal hormones, like cortisol, to decrease. For patients who have problems with blood clotting and are taking anticoagulants to thin the blood, you may not be able to take Synthroid.

Because this medication is identical to the naturally occurring hormone, it’s safe to take during pregnancy. It’s not known whether mothers can breastfeed while taking it, as there is limited knowledge about whether it ends up in breastmilk.

Side Effects

There are many side effects that can come from using Synthroid, but don’t stop taking the medication unless your doctor tells you to. Some of the most common side effects are: hot flashes, sweating, fever, headaches, being more sensitive to heat, feeling irritable or nervous, having trouble sleeping, weight changes, nausea, hair loss, menstrual period changes, and appetite and weight changes. These side effects may go away or get better as your body gets used to the medication.

If you have serious side effects from Synthroid, your doctor needs to know right away, and you may need immediate medical care. The serious side effects include: irregular heartbeats or fast heartbeats, a high fever, shortness of breath, feeling weak, feeling too cold, chest pain, tremors, memory problems, depression, muscle aches, leg cramps, severe hair loss, diarrhea, and vomiting.

There are some very severe side effects that generally require emergency medical care. These include: a sudden loss of vision, eye swelling or pain, tunnel vision, blurry vision, or seeing bright halos around the lights you see. Other severe side effects include pounding heartbeats, irregular heartbeats, sudden dizziness, slurred speech, passing out, loss of coordination and trouble walking, stiff muscles, and feeling a fluttering in the chest.

Drug Interactions

There are several types of medications that can cause adverse effects if you’re also taking Synthroid. Your doctor needs to know everything that you’re taking, even if it’s over the counter, before you’re prescribed this medication. These are some diabetes drugs that shouldn’t be used with Synthroid. Other potential problems include some heartburn drugs such as Prilosec, some medications for digestive problems like Gas-X, and some antidepressants like tricyclic antidepressants.

Strengths and Dosages

Synthroid is usually prescribed in tablet form. There are many different strengths of these pills available, running from 25 mcg to 300 mcg. You may start out on a small dose and gradually have the dosage raised as your body adjusts to Synthroid. When it’s delivered by injection, you may be started with a loading dose that is anywhere from 300 mcg to 500 mcg. Then, the maintenance doses are generally between 50 mcg and 100 mcg every day. The medication will start to work immediately, but you may not feel the difference for a few weeks.


Usually, Synthroid is prescribed for use once a day. If you’re taking the tablet or capsule, take it anywhere from 30 minutes to an hour before you have your breakfast to allow for better absorption. Take it exactly as it’s prescribed. Swallow the medicine whole and take it with a full (8 ounce) glass of water. Otherwise, the pill can get caught in your throat. Make sure that you take it as prescribed every day. Your doctor may suggest that you take it at the same time every day to keep your levels of the medication steady.

When children take it, a tablet is often crushed and mixed into water or another liquid. Once you crush up the pill, don’t store it or keep it much longer. Wait until it’s time to give the dose to crush it.

Continue taking the medication every day. If you have hypothyroidism, Synthroid can keep it well under control. However, it’s not a cure. Even if it makes you feel well, you can’t stop taking it. If you were to quit taking it, all of the symptoms you had of hypothyroidism would return. Generally, patients are on this medication for the rest of their lives. Be sure to go to all of your follow-up doctor’s appointments. You may need to have medical tests done while you’re taking this medication, and the dose may need to be changed over time. Never share this medication with anyone else.

Cost of Synthroid

The price that you pay for Synthroid will vary a lot from patient to patient. What you actually pay depends a lot on whether you have insurance and what your insurance plan is. The price also depends on the pharmacy that you use and any coupons you may have for it. If you need some financial assistance with paying for this medication, there is help available. The maker of this medication, AbbVie Inc., has a few ways to help patients save on it. This includes making coupons available as well as a co-


The generic versions of this medication are possible alternatives, depending on what your doctor wants to prescribe. There is also a different type of medication for hypothyroidism called Armour Thyroid. While Synthroid is a synthetic way to replace this hormone, Armour Thyroid is derived from animals.

IMPORTANT NOTE: The information provided here is for educational purposes only and is not intended to serve as medical advice, diagnosis, or treatment recommendations. It should not be taken as an endorsement of any specific medication or treatment. Individual health conditions and responses to treatment can vary greatly; therefore, this information should not be seen as a guarantee of safety, suitability, or effectiveness for any particular individual. Always consult with a healthcare professional for personalized medical advice and before making any decisions regarding your health or treatment plans.

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