Compare Synthroid vs. Armour thyroid

Head-to-head comparisons of medication uses, side effects, ratings, and more.

Synthroid
(Levothyroxine)

Armour Thyroid
(Thyroid Hormone)

Replaces thyroid hormones. 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.Replaces thyroid hormones. Armour Thyroid (Thyroid Hormone) can be used to treat low thyroid hormone, but it's not recommended by most doctors and isn't available in generic.
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Reviews & ratings
Button Group. All currently active
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5.60036832412523Synthroid
Reviews for Synthroid (Levothyroxine)
74%
of people say Synthroid (Levothyroxine) is worth it
62%
say it works well
10%
say it's a big hassle

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Side effects
SynthroidArmour thyroid

The Synthroid FDA package insert doesn’t have numbers about how common side effects are.

More about Synthroid side effects »

We haven’t found good data for Armour thyroid side effects.

FDA side effect reports for Armour thyroid »
How it works
SynthroidArmour thyroid
Synthroid (Levothyroxine) is a synthetic version of a hormone made by your thyroid gland. Thyroid hormones affect many important bodily functions, like controlling metabolism and telling your body how to use energy sources.Armour Thyroid (Thyroid Hormone) is a hormone replacement medicine for people with hypothyroidism. Thyroid hormone regulates metabolism, which is everything your body does to turn food into energy. It affects almost every cell in your body.
Type of medication
SynthroidArmour thyroid
Thyroid supplementPrescription only
Thyroid supplementPrescription only
Available as
SynthroidArmour thyroid
  • Pill
  • Pill
Used for (click to learn more)
SynthroidArmour thyroid
Risk factors for serious side effects
SynthroidArmour thyroid
  • Current heart disease
  • Age 60 or older
  • Taking Synthroid (Levothyroxine) with certain types of stimulant medicines
      • Duration of treatment
      • Postmenopausal women
        Detailed Synthroid (Levothyroxine) risks & warnings »
        • Taking Armour Thyroid (Thyroid Hormone) for weight loss
        • Diabetes
        • Taking blood thinners
        Detailed Armour Thyroid (Thyroid Hormone) risks & warnings »
        Pregnancy category
        SynthroidArmour thyroid
        AFDA pregnancy category (Safe)

        Research studies with real people haven’t found any risk to unborn babies in the first trimester. There’s no evidence of risk later in pregnancy, either.

        See the FDA package insert
        AFDA pregnancy category (Safe)

        Research studies with real people haven’t found any risk to unborn babies in the first trimester. There’s no evidence of risk later in pregnancy, either.

        See the FDA package insert
        Alcohol
        No specific alcohol-related info.No specific alcohol-related info.
        Food
        • Absorption is easily affected by food and other medicines.
        • 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.
        No specific food-related info.
        Kidneys and liver
        No specific kidneys and liver-related info.No specific kidneys and liver-related info.
        Sex
        No specific sex-related info.No specific sex-related info.
        Sleep
        • 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.
        No specific sleep-related info.
        Weight
        • 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.
        • It is not recommended to take Armour Thyroid (Thyroid Hormone) for weight loss if your thyroid is working normally. You can get an overdose of thyroid hormone, which can be toxic or even deadly, especially if you are on other medications for losing weight. Talk to your doctor for suggestions to lose weight safely. Symptoms of increased thyroid hormone include irregular heartbeat, tremors, insomnia, vomiting or restlessness.
        Upsides and benefits
        SynthroidArmour thyroid
        • 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.
        • Cheap.
        • Made from animal sources (pigs), so it's considered natural.
        Downsides and risks
        SynthroidArmour thyroid
        • 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.
        • Not recommended by doctors because of the inconsistency of thyroid hormone in each tablets, and the fact that it hasn't been studied as much as similar medications.
        • Not available in generic.
        Tips from our pharmacists for people taking the medication
        SynthroidArmour thyroid
        • 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.
        • Take on an empty stomach.
        • Take at the same time every day.
        • Space out colestipol or cholestyramine by at least 4 hours.
        Learn more
        More about SynthroidSide effectsReviews & ratingsAlternativesFDA package insert
        More about Armour thyroidSide effectsReviews & ratingsAlternativesFDA package insert