Replaces thyroid hormones.
Our pharmacists’ bottom line
Synthroid (Levothyroxine) is an important replacement hormone when your body can't make enough thyroid hormone. It's easily affected by food, other medicines or supplements, and health conditions, so you should try to take it exactly as instructed.
- Supplies an essential hormone that your body needs to function. Works well to improve symptoms of an underactive thyroid.
- Safe to use for any age range and pregnant women.
- Absorption is easily affected by food and other medicines.
- Not one-dose-fits-all: Dose adjustments are usually needed when starting the medicine and when your health changes.
- Routine blood tests are needed at least yearly and more during dose adjustments, but it takes a long time to see full effect (6 to 8 weeks).
- Different brands of Levothyroxine may not work the same. Ask your pharmacist if your refill looks different than your old pills. Synthroid is one of the few drugs where the brand really does work better than the generic for many people.
- Lots of drug interactions, so check with your pharmacist before taking anything new.
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Side effects for Synthroid (Levothyroxine)
Manufacturers don’t say how common these side effects are
- Abdominal cramps
- Abnormal heart rhythm
- Abnormally fast heart beat
- Elevations in liver function tests
- Excessive sweating
- Hair loss
- Heart attack
- Heart failure
- Heart pounding or racing sensation
- Heart-related chest pain
- Heat intolerance
- Increased appetite
- Increased pulse and blood pressure
- Mood swings
- Muscle weakness
- Shortness of breath
- Sleep difficulty
- Stopped heart and circulation
- Weight loss
What to expect when you start Synthroid (Levothyroxine)Skip what to expect section. Skip to Risks & Warnings section.
- This is one of the few drugs where the brand really does work better than the generic for some people.
- Food prevents Levothyroxine absorption. Take it on an empty stomach with a full glass of water at least 30 minutes before breakfast and other medicines. If this is too much of a hassle for you and you end up skipping your medicine, it's better to just take it whenever you want, and your doctor can increase the dose if needed.
- Separate by at least 4 hours from any antacids, calcium or iron supplements, and multivitamins.
- Starts working in 1 to 2 weeks. Full effects in 6 to 8 weeks.
- Can cause irregular heart rate, anxiety, sweating, or trouble sleeping until your body gets used to the medicine. Side effects might not go away if the dose is too high for you.
- Requires regular blood tests.
- Not all generics and brands are the same. Double-check with your pharmacist that you have the right medicine for you.
Risks and Warnings for Synthroid (Levothyroxine)Skip Risks and Warnings section. Skip to Tips section.
- Higher risk if:
- › Current heart disease
- › Age 60 or older
- › Taking Synthroid (Levothyroxine) with certain types of stimulant medicines
Taking Synthroid (Levothyroxine) can cause new or worsen heart problems. Call your doctor or get medical care right away if you have rapid or irregular heartbeats, chest pain or shortness of breath. These symptoms may be serious and due to overtreatment of Synthroid (Levothyroxine). You may need to stop taking your medicine for one week, then re-start at a lower dose.
Tips from pharmacists and people taking Synthroid (Levothyroxine)Final section. Do you want to return to drug navigation?
- Upsides and downsides from our pharmacists
- › Absorption is easily affected by food and other medicines.
- Tips from our pharmacists
- › Food prevents Levothyroxine absorption. Take it on an empty stomach with a full glass of water at least 30 minutes before breakfast and other medicines. If this is too much of a hassle for you and you end up skipping your medicine, it's better to just take it whenever you want, and your doctor can increase the dose if needed.
- I would give up a meal in order to get my prescription filled - effects of hypothyroid condition too miserable to consider doing without this drug.Taken for: HypothyroidismDuration taken: two years or more
- Having to take it early, before coffee or breakfast, is inconvenient, but totally worth it when you get your energy back. Also, I found that it didn't work nearly as well for me till I started regulating my blood sugar through better diet choices. I don't feel hypo any more!Age: 34Gender: womanTaken for: HypothyroidismDuration taken: a year or so
- Sometimes it is really hard to take it early enough before breakfast.Age: 44Gender: womanTaken for: Hypothyroidism
- Tips from our pharmacists
- › Can cause irregular heart rate, anxiety, sweating, or trouble sleeping until your body gets used to the medicine. Side effects might not go away if the dose is too high for you.
- Risks from our pharmacists
- › don't take Synthroid (Levothyroxine) for weight loss or obesity. It’s not recommended, safe or effective for this use, especially if you don't have any issues with your thyroid. Taking high doses of Synthroid (Levothyroxine) can cause serious or fatal effects especially if used with other medications for weight loss. Talk to your doctor before about other medicines you can take to treat your condition.
- The generic worked fine for me for probably 8 years but the last 2 have been awful -- terrible weight gain, depression, constipation. Blood work shows it's working just right but clearly something is wrong.Age: 39Gender: womanTaken for: HypothyroidismDuration taken: two years or more
- It takes time to take effect & the weight gained because of a slow thyroid did not just fall off-took me 5 years to lose.Age: 61Gender: womanDuration taken: two years or more
- Talk to your doctor if you still feel sluggish at your dose. It took me a while to get mine right, but I have been ok and weight-stable etc for years now.Age: 35Gender: womanTaken for: HypothyroidismDuration taken: two years or more