levothyroxine
Levothyroxine (Synthroid) is used to treat low thyroid hormone levels. It's also used to treat a certain type of thyroid cancer. Levothyroxine (Synthroid) is available as an oral pill and liquid. This medication taken by mouth once daily. It's best to take levothyroxine (Synthroid) an empty stomach because it has many interactions with other medications and food. Side effects of levothyroxine (Synthroid) include headache, nervousness, trouble sleeping, and weight loss.
What is Levothyroxine (Synthroid)?
What is Levothyroxine (Synthroid) used for?
Hypothyroidism (low thyroid hormone levels)
Thyroid cancer (in combination with radiation and surgery)
How Levothyroxine (Synthroid) works
Levothyroxine (Synthroid) is a man-made version of the T4 thyroid hormone made by your thyroid gland. Thyroid hormones have important functions like controlling metabolism, body temperature, heart rate, and more. When the amount of hormone is too low, taking thyroid replacement hormones can bring your levels back to normal.
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What are the side effects of Levothyroxine (Synthroid)?
Common Side Effects
- Irregular heartbeat
- Chest pain
- Shortness of breath
- Leg cramps
- Headache
- Nervousness
- Hives or skin rash
- Irritability
- Trouble sleeping
- Tremors
- Muscle weakness
- Change in appetite
- Weight loss
- Vomiting
- Diarrhea
- Sweating a lot
- Sensitivity to heat
- Fever
- Changes in menstrual period
Other Side Effects
- Tiredness
- Anxiety
- Muscle spasm
- Fast heart rate
- Stomach cramps
- Hair loss
- Flushing
- Rash
Serious Side Effects
- Heart failure: trouble breathing, weakness, tiredness, swelling in the hands, ankles, and feet
- Heart attack: dizziness, lightheadedness, anxiety, trouble breathing, fast heartbeat, nausea, cold sweat, clammy skin, chest pain or tightness
Source: DailyMed
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The following side effects have also been reported
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:
Less common
Chest pain or discomfort
decreased urine output
difficult or labored breathing
difficulty with swallowing
dilated neck veins
extreme fatigue
fainting
fast, slow, irregular, pounding, or racing heartbeat or pulse
heat intolerance
hives or welts, skin itching, rash, or redness
irregular breathing
irritability
menstrual changes
pain or discomfort in the arms, jaw, back, or neck
sweating
swelling of the eyes, face, lips, throat, or tongue
tightness in the chest
Get emergency help immediately if any of the following symptoms of overdose occur:
Symptoms of overdose
Change in consciousness
cold, clammy skin
confusion
disorientation
fast or weak pulse
lightheadedness
loss of consciousness
sudden headache
sudden loss of coordination
sudden slurring of speech
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
Less common
Abdominal or stomach cramps
change in appetite
crying
false or unusual sense of well-being
fear or nervousness
feeling not well or unhappy
feeling of discomfort
feeling of warmth
feeling things are not real
feelings of suspicion and distrust
headache
increased appetite
mental depression
muscle weakness
quick to react or overreact emotionally
rapidly changing moods
redness of the face, neck, arms, and occasionally, upper chest
restlessness
trouble getting pregnant
trouble sitting still
unusual tiredness or weakness
vomiting
weight gain or loss
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
Pros and cons of Levothyroxine (Synthroid)
Pros
First-choice medication for treating low thyroid hormone levels
Safe to use for all ages and during pregnancy
Some forms have a lower-cost generic available
Available as a liquid solution for people who have trouble swallowing pills (Tirosint Sol, Thyquidity, and Ermeza)
Only needs to be taken once a day
Cons
Might take months to find the right dose
Takes 4 to 6 weeks to see the full effects
Need to get regular blood tests to make sure you're taking the right dose
Interacts with many types of food, drinks, medications, and supplements
Works best if taken on an empty stomach
Pharmacist tips for Levothyroxine (Synthroid)
Take levothyroxine (Synthroid) 30 minutes to 1 hour before breakfast on an empty stomach. This will help the full amount of medication get absorbed in your body.
It's important to keep all of your follow-up appointments for laboratory testing while taking levothyroxine (Synthroid). Your provider will adust your dose based on your thyroid hormone level test results.
Most of the side effects of levothyroxine (Synthroid) are symptoms of hyperthyroidism (high thyroid hormone levels). If you experience symptoms like anxiety or fast heart rate, talk with your provider because it might mean your dose of levothyroxine (Synthroid)is too high.
Take levothyroxine (Synthroid) at least 4 hours apart from aluminum-, calcium- or iron- containing medications and supplements, including antacids like calcium carbonate (Tums). This is because these medications can prevent your body from absorbing levothyroxine (Synthroid) properly.
You might experience some hair loss during the first few months of starting levothyroxine (Synthroid). This is usually temporary and should get better with time.
There are many brands and formulations of levothyroxine available. Your body might not respond in the same way to all forms of levothyroxine (Synthroid). It's best to try to stick with the same generic or the same brand of levothyroxine consistently. Don't switch manufacturer of your levothyroxine without speaking to your provider first. If you do switch to a different form of levothyroxine, your provider might order blood work to check your thyroid level to make sure its working well for you.
If you're taking Tirosint Sol liquid solution, you can squeeze the medication directly into your mouth from the small vials or onto a spoon to take. You can also squeeze the medication into a cup of water, stir well, and then drink the mixture right away. Pour more water into the cup, swish, and drink the water to make sure you've taken all of the medication. Don't mix the medication with any other liquid besides water.
If you're taking Thyquidity or Ermeza liquid solution, measure your doses using the measuring syringe provided by the pharmacy. Don't use household or kitchen measuring spoons, since they might not be accurate and cause you to take the wrong dose.
Check the packaging or ask your pharmacist when you should discard levothyroxine (Synthroid). Depending on the form you're using, the directions will differ. For example, Ermeza and Tirosint Sol should be thrown away 3 months after opening the container, while Thyquidity lasts 2 months after opening.
More on Levothyroxine (Synthroid) tips
Frequently asked questions about Levothyroxine (Synthroid)
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What are the risks and warnings for Levothyroxine (Synthroid)?
Levothyroxine (Synthroid) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.
Not for weight loss
Risk factors: Taking other medications for weight loss
Levothyroxine (Synthroid) shouldn't be used for weight loss. It’s not recommended, safe, or effective for this use. Taking high doses of levothyroxine (Synthroid) can cause serious or fatal effects especially if used with other medications for weight loss.
Heart problems
Risk factors: Current heart disease | Age 65 or older
Taking too much levothyroxine (Synthroid) can cause heart problems, especially for older adults or people with heart conditions. Call your provider or get medical care right away if you have rapid or irregular heartbeat, chest pain, or trouble breathing. Your provider might need to reduce your dose or have you stop taking the medication if you experience new heart problems.
Dangerously low stress hormone levels (adrenal crisis)
Risk factors: Adrenal insufficiency | Addison's disease
In rare cases, some people can have low thyroid hormones and low adrenal hormones at the same time. If you have conditions, such as Addison's disease, where your body has low adrenal hormone levels, let your provider know. It's important that they treat your hormone levels first before they treat your thyroid condition. Otherwise, receiving thyroid hormones first can cause your adrenal hormones to drop even lower and make you feel unwell. Your provider should check your adrenal hormones before prescribing levothyroxine (Synthroid). If you experience long-lasting tiredness, stomach pain, dizziness, weakness, or vomiting while taking levothyroxine (Synthroid), seek medical attention right away.
Worsening diabetes
Risk factors: Taking diabetes medications
Levothyroxine (Synthroid) can raise your blood sugar levels, especially when you first start this medication and when your provider raises your dose. If you already have diabetes, your provider might need to adjust the dose of your blood sugar medications. Check your blood sugar levels as directed by your provider. Talk to your provider if the levels are higher than usual.
Effects on bones
Risk factors: Postmenopausal females | Higher doses
Taking levothyroxine (Synthroid) can weaken bones over time, especially if your dose is too high. The risk is higher for females after menopause . To lower your risk, your provider will be monitoring your thyroid levels to make sure you're taking the lowest dose needed to treat your thyroid condition. Make sure to get plenty of exercise, eat a bone-healthy diet, and avoid alcohol to lower your risk of bone problems.
Levothyroxine (Synthroid) dosage forms
| Dosage | Quantity | Price as low as | Price per unit |
|---|---|---|---|
| 30 capsules of 13mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 25mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 50mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 75mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 88mcg | 1 box | $53.91 | $53.91 |
| 30 capsules of 100mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 112mcg | 1 box | $53.91 | $53.91 |
| 30 capsules of 125mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 137mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 150mcg | 1 box | $53.91 | $53.91 |
| 30 capsules of 175mcg | 1 box | $52.79 | $52.79 |
| 30 capsules of 200mcg | 1 box | $52.79 | $52.79 |
| Dosage | Quantity | Price as low as | Price per unit |
|---|---|---|---|
| 25mcg | 90 tablets | $9.90 | $0.11 |
| 50mcg | 30 tablets | $4.00 | $0.13 |
| 75mcg | 90 tablets | $9.90 | $0.11 |
| 88mcg | 90 tablets | $9.90 | $0.11 |
| 100mcg | 90 tablets | $9.90 | $0.11 |
| 112mcg | 90 tablets | $10.00 | $0.11 |
| 125mcg | 90 tablets | $9.90 | $0.11 |
| 137mcg | 90 tablets | $10.00 | $0.11 |
| 150mcg | 90 tablets | $10.00 | $0.11 |
| 175mcg | 90 tablets | $10.00 | $0.11 |
| 200mcg | 90 tablets | $10.00 | $0.11 |
| 300mcg | 90 tablets | $25.22 | $0.28 |
Typical dosing for Levothyroxine (Synthroid)
Your provider will calculate your dose of levothyroxine (Synthroid) based on different factors, such as your age, medical condition, and level of thyroid hormone.
The typical dose of levothyroxine (Synthroid) ranges from 13 mcg to 200 mcg taken by mouth once daily on an empty stomach.
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Interactions between Levothyroxine (Synthroid) and other drugs
More on Levothyroxine (Synthroid) interactions
Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Aluminum Carbonate, Basic
- Aluminum Hydroxide
- Aluminum Phosphate
- Calcium Acetate
- Calcium Carbonate
- Calcium Citrate
- Chlorotrianisene
- Cholestyramine
- Chromium
- Ciprofloxacin
- Colesevelam
- Conjugated Estrogens
- Conjugated Estrogens Synthetic A
- Conjugated Estrogens Synthetic B
- Dexlansoprazole
- Dienestrol
- Diethylstilbestrol
- Dihydroxyaluminum Aminoacetate
- Dihydroxyaluminum Sodium Carbonate
- Esomeprazole
- Esterified Estrogens
- Estradiol
- Estramustine
- Estriol
- Estropipate
- Ethinyl Estradiol
- Fosphenytoin
- Imatinib
- Iron
- Kelp
- Lansoprazole
- Lanthanum Carbonate
- Lopinavir
- Magaldrate
- Magnesium Carbonate
- Magnesium Hydroxide
- Magnesium Oxide
- Magnesium Trisilicate
- Mestranol
- Omeprazole
- Pantoprazole
- Patiromer
- Phenytoin
- Polyestradiol Phosphate
- Promestriene
- Quinestrol
- Rabeprazole
- Rifampin
- Ritonavir
- Semaglutide
- Sevelamer
- Simvastatin
- Tibolone
How much does Levothyroxine (Synthroid) cost?
Levothyroxine (Synthroid) contraindications
Uncorrected adrenal insufficiency
What are alternatives to Levothyroxine (Synthroid)?
Hypothyroidism (low thyroid hormone levels)
Thyroid cancer (in combination with radiation and surgery)
Hypothyroidism (low thyroid hormone)
Lowering thyroid-stimulating hormone (TSH) levels in people with other thyroid problems like goiters or thyroid cancer
Hypothyroidism (low thyroid hormone levels)
Thyroid cancer (together with radiation and surgery)
What is the latest news about Levothyroxine (Synthroid)?
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References
Best studies we foundAscent Pharmaceuticals, Inc. (2023). LEVOTHYROXINE SODIUM tablet [package insert]. DailyMed.
Haddady, S. (2018). Body weight appears to be the main levothyroxine dose adjustment variable. Clinical Thyroidology for the Public.
IBSA Pharma Inc. (2023). TIROSINT SOL- levothyroxine sodium solution TIROSINT SOL- levothyroxine sodium solution [package insert]. DailyMed.
Jonklaas, J., et al. (2014). Guidelines for the treatment of hypothyroidism: Prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid.
Mylan Specialty L.P. (2022). ERMEZA- levothyroxine sodium solution [package insert]. DailyMed.
VistaPharm, Inc. (2022). THYQUIDITY- levothyroxine sodium solution [package insert]. DailyMed.
Wiesner, A., et al. (2021). Levothyroxine interactions with food and dietary supplements–A systematic review. Pharmaceuticals.
You and Your Hormones. (2021). Thyroxine.
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