Synthroid (Levothyroxine Sodium)
Synthroid
Levothyroxine Sodium
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Eltroxin
Levothyroxine Sodium
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Levoxyl
Levothyroxine
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Tirosint
Levothyroxine Sodium
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Synthroid (Levothyroxine Sodium)

What is Synthroid (Levothyroxine Sodium)?

Synthroid is a medication prescribed to replace a hormone (thyroxine) that is normally produced by the thyroid gland. When the thyroid gland can’t produce enough thyroxine, thyroid hormone levels in the blood are decreased (hypothyroidism). This leads to reduced metabolism and can affect organ function in the body. Additionally, the thyroid hormone is important for mental and physical activity, as well as childhood development. Synthroid replaces thyroxine with levothyroxine sodium to prevent hypothyroidism symptoms.

Dosage

Synthroid should be taken orally on an empty stomach, 30 minutes to one hour before breakfast. This medication is typically taken once daily unless instructed otherwise by your doctor. The capsule form of Synthroid must be swallowed whole, without chewing, crushing, or splitting it beforehand. The tablet form is suitable for people who cannot swallow the capsule whole. Infants and children should be given the tablet crushed in 1-2 teaspoons of water. Dosage in this form should not be prepared in advance, it is best to crush the tablet and give it to the infant straight away.

Dosage is calculated based on age, weight, the severity of the medical condition, response to treatment, and laboratory results. Thyroid hormone replacement is typically taken for life. Do not stop or change the dosage of this medication without talking to your doctor first.

Storage

Synthroid should be stored at room temperature (below 25°C), out of direct sunlight, and away from moisture. Keep out of reach of children and pets. Do not use expired medication, dispose of all expired or surplus medication responsibly following the instructions of your doctor or pharmacist. Do not flush medication down the toilet or sink.

Side Effects

Common Side Effects

All medications come with a risk of side effects. It is important to recognize that your doctor will have determined that the risk of side effects is outweighed by the potential benefit of this medication. Side effects are felt differently by everyone, and it is possible you will not experience any. Common side effects with Synthroid are:

  • Hair loss (temporary)
  • Menstrual irregularities
  • Diarrhea
  • Weight loss or gain
  • Muscle weakness
  • Nervousness
  • Vomiting
  • Sweating

Severe Side Effects

On rare occasions, Synthroid can be associated with severe side effects that should be taken seriously. These include but are not limited to:

  • Increased sweating
  • Heat sensitivity
  • Mood swings
  • Fatigue
  • Tremor
  • Headache
  • Shortness of breath
  • Bone pain
  • Easily broken bones

Seek emergency medical help if you experience any of the following:

  • Chest pain
  • Pounding/irregular heartbeat
  • Swollen hands, feet, or ankles
  • Seizures
  • Symptoms of an allergic reaction: rash, itching, facial swelling, difficulty breathing, severe dizziness

This is not an exhaustive list of side effects. If you experience anything unusual that causes concern, your symptoms worsen, or do not resolve on their own, contact your healthcare provider right away.

Warnings & Precautions

Allergies

Ensure your doctor is aware of any allergies you have, particularly if you are allergic to the active ingredient levothyroxine, or any of the other ingredients of Synthroid. Tell your doctor if you have had a severe allergic reaction to anything in the past, and the symptoms you experienced.

Medical History

Prior to starting Synthroid, make sure your doctor knows your medical history, particularly if you have a history of increased thyroid hormones (thyrotoxicosis), reduced adrenal gland function, heart disease, hypertension, and diabetes.

Diabetes

Synthroid can affect your blood sugar. While you are taking Synthroid, ensure you check your blood sugar regularly and communicate with your doctor. If you have symptoms such as excessive thirst and/or urination, shakiness, abnormal sweating, dizziness, or hunger, your doctor will likely need to change your medication, exercise, or dietary schedule.

Surgery

Always let your doctor know what medications (prescription and non-prescription) you take regularly prior to having surgery.

Pediatric Use

Children may have a higher sensitivity to side effects such as headaches, vision changes, and lower limb pain. High thyroid hormone levels in children can stunt bone growth and development, so it is important to keep in regular contact with your doctor to monitor the treatment progress.

Geriatric Use

There is evidence to suggest that older adults and the elderly can have a higher sensitivity to side effects such as pounding/irregular heartbeat. This should be monitored while you are taking this medication.

Pregnancy

Studies have shown that Synthroid can be taken while pregnant. Consult your doctor first as your dose or other factors may need to be adjusted.

Breastfeeding

It has been shown that levothyroxine can pass into breast milk, however, it is unlikely to pose any risk to the infant. Check with your doctor if you are concerned.

Synthroid should only be used to treat the condition it is prescribed for. Do not take Synthroid for any other purpose. Do not share this medication with anyone, even if they have the same condition as you. Do not take expired medication. Do not stop taking Synthroid or change the dosage unless your doctor tells you to. Do not mix brands of the active ingredient levothyroxine without consulting your doctor first.

Interactions & Contraindications

Medications that are taken at the same time can sometimes interact with one another, changing how they work or increasing the risk of side effects. Ensure your doctor is aware of all medications you regularly take, including non-prescription. Do not change the dosage, stop, or start taking any medication without consulting your doctor first.

Some medications can change the way thyroid hormone is absorbed by the body and should therefore not be taken within four hours of taking Synthroid. These include cholestyramine, colestipol, colesevelam, antacids, blood thinners, digoxin, sucroferric oxyhydroxide, iron, calcium supplements, phosphate bingers, glucocorticoids, statins, asthma medication, cold medicine, some antibiotics, some forms of cancer treatment, weight loss medication, epilepsy medication, painkillers such as ibuprofen or paracetamol, and hormone replacement therapy (estrogen or testosterone).

Frequently Asked Questions

Thyroid supplements are typically taken for life. Keep taking Synthroid for as long as your doctor tells you to. It works to control your condition, but it is not a cure.

If you miss a dose, take it as soon as you remember. If you remember close to the time to take your next scheduled dose, skip the missed dose altogether. Take your next dose as scheduled. Do not take both to catch up unless your doctor instructs you to do so. If you miss two or more doses in a row, contact your doctor.

If you suspect an overdose, contact your doctor immediately or go to the closest hospital. Take your tablets with you, and tell the staff how much you took.

People who have overactive thyroid glands (thyrotoxicosis) should not take Synthroid. It is also not advised for people with untreated adrenal gland under-activity, a history of cardiac events, pregnant people taking anti-thyroid agents, or people with an allergy to any of the ingredients.

Synthroid is absorbed better on an empty stomach.

By stopping Synthroid suddenly, you risk worsening your condition and developing unwanted side effects. If you wish to come off Synthroid, your doctor will likely gradually decrease your dose before stopping it completely.