Buy Levothyroxine (Synthroid) — Online Prescription
Levothyroxine is the generic name behind Synthroid — the synthetic thyroid hormone that treats hypothyroidism and is one of the most-prescribed medications in the country. Here's how it actually works, why timing and consistency matter more than with most pills, the boxed warning most pages bury, and what it costs.
Medically reviewed Medically reviewed by Darcey Melnyk, Pharmacist — NPI 1740713718 · Last updated 2026-09-10
| Active ingredient | Levothyroxine |
|---|---|
| Dosage form | Tablet, capsule, oral solution, IV injection |
| Administration route | Oral, intravenous |
Indications: 1 INDICATIONS AND USAGE Hypothyroidism SYNTHROID is indicated in adult and pediatric patients, including neonates, as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. Pituitary Thyrotropin (Thyroid -Stimulating Hormone, TSH) Suppression SYNTHROID is indicated in adult and pediatric patients, including neonates, as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-dif…
Boxed warning: WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life - threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects [see Adverse Reactions ( 6 ), Drug Interactions ( 7.7 ), and Overdosage …
Contraindications: 4 CONTRAINDICATIONS SYNTHROID is contraindicated in patients with uncorrected adrenal insufficiency [see Warnings and Precautions ( 5.4 ) ] . Uncorrected adrenal insufficiency. ( 4 )
openFDA label data — Updated 2026-09-10Levothyroxine is the generic name for the medication sold under the brand Synthroid — a synthetic version of T4, the hormone your thyroid gland normally produces, prescribed to treat hypothyroidism (an underactive thyroid). It is not a controlled substance and not available over the counter as a real thyroid hormone. It carries an FDA boxed warning against using it for weight loss, and — unusually for a medication — it's something you generally should keep taking, not stop, if you become pregnant. Because it has a narrow therapeutic index, timing, food, and dose consistency matter more with this drug than with most pills.
What levothyroxine is, and how it works
Levothyroxine is a synthetic (lab-made) version of thyroxine, also called T4 — one of the two main hormones your thyroid gland produces naturally. In someone with hypothyroidism, the thyroid doesn't make enough of this hormone on its own, which slows down metabolic processes throughout the body: energy production, heart rate, digestion, temperature regulation, and more. Taking levothyroxine replaces what the thyroid isn't making, at a dose calibrated to bring your levels back to a normal range.
Once absorbed, levothyroxine works exactly like your body's own T4: your tissues convert some of it into T3 (triiodothyronine), the more metabolically active thyroid hormone, as needed. That's a key reason levothyroxine alone — rather than a T3-containing product — is standard first-line treatment: your body handles the T4-to-T3 conversion itself, rather than needing it dosed directly.
- Hypothyroidism — the primary approved use, including Hashimoto's thyroiditis (the most common cause of hypothyroidism in the US, an autoimmune condition).
- Pituitary TSH suppression — used at higher, carefully monitored doses in certain thyroid cancer and nodule management protocols, a different goal from standard replacement.
- Congenital hypothyroidism — a distinct pediatric dosing and monitoring protocol, since untreated hypothyroidism in infancy affects growth and neurological development.
Levothyroxine vs. Synthroid: generic and brand names
Straightforward on the surface — Synthroid is one brand of levothyroxine, generic levothyroxine is the same active ingredient — but this drug has a real nuance most pages skip entirely.
Synthroid
- What it is
- The market-leading brand, made by AbbVie, first approved decades ago
- Availability today
- Widely stocked; some insurance plans and some patients specifically prefer staying on it
- Cost
- Higher cash price than generic, though AbbVie's direct cash program can narrow the gap
Levothyroxine sodium
- What it is
- The active ingredient itself, made by multiple FDA-approved manufacturers
- Availability today
- The default fill for most prescriptions; specific manufacturer can vary by pharmacy stock
- Cost
- Meaningfully lower cash price than brand
The FDA classifies levothyroxine as a narrow therapeutic index (NTI) drug — the gap between an under-treating dose and an over-treating one is relatively small. Because of that, the FDA actually requires tighter bioequivalence testing for generic levothyroxine than for most generic drugs. Recent FDA-sponsored real-world research found that patients who switched between well-regulated generic products generally achieved the same outcomes as patients who stayed on one product — reassuring, but it's still true that a pharmacy can fill a different manufacturer's generic from one refill to the next without necessarily flagging it to you. Many endocrinologists recommend asking your pharmacy to keep you on the same manufacturer consistently when practical, and getting a TSH recheck about 6 weeks after any confirmed brand or manufacturer change. This is a case where "generic vs. brand" is less important than "same product, consistently."
How and when to take it — timing, food, and coffee
This is where levothyroxine differs most from a typical daily pill — how and when you take it measurably affects how much actually reaches your bloodstream.
- Take it on an empty stomach — the FDA label specifies 30 to 60 minutes before breakfast, consistently, ideally at the same time each day.
- Wait on coffee. Research published by the American Thyroid Association has found coffee (and tea) taken at the same time as, or shortly after, a dose can reduce absorption by roughly 27–36%. Wait at least 30–60 minutes after your dose before your morning coffee.
- Separate it from calcium and iron by at least 4 hours. Calcium supplements, many multivitamins, and iron supplements bind to levothyroxine in the gut and meaningfully reduce absorption — this includes calcium-fortified foods and antacids.
- Watch high-fiber meals, soy, and walnuts if taken close to your dose — the FDA label specifically notes soybean flour, cottonseed meal, walnuts, and dietary fiber can bind and reduce absorption.
- Be consistent, not just careful. A single off day rarely matters much (levothyroxine's half-life is about a week), but a genuinely consistent routine — same time, same relationship to food, same product — is what actually keeps your TSH stable, more than any single rule in isolation.
Biotin (vitamin B7, common in hair/skin/nail supplements) can interfere with the lab assay used to measure TSH and T4, producing an inaccurate result — not because it affects the drug itself, but because it distorts the test. The FDA label specifically advises stopping biotin at least 2 days before any thyroid lab work. If your TSH result seems inconsistent with how you feel, ask whether you were told to pause biotin beforehand.
Dosing: starting dose and titration
Levothyroxine dosing is individualized and always based on lab monitoring — the figures below are the FDA-labeled starting-dose framework for adults, not a substitute for your prescriber's specific plan.
| Patient group | Starting approach | Titration |
|---|---|---|
| Typical adult with primary hypothyroidism | Full replacement ≈ 1.6 mcg/kg/day; some need a lower starting dose | Adjust by 12.5–25 mcg every 4–6 weeks based on TSH/free-T4 |
| Adults with cardiac disease or at risk of atrial fibrillation | Lower starting dose than full replacement | Slower titration, every 6–8 weeks |
| Geriatric patients | Lower starting dose | Titrated more cautiously, given cardiac sensitivity |
| Pediatric patients | Weight- and age-based (ranges from about 10–15 mcg/kg/day in infants down to 1.6 mcg/kg/day once growth is complete) | Titrated roughly every 2 weeks under close monitoring |
Per the FDA label, daily doses greater than 200 mcg are seldom required, and a lack of response to more than 300 mcg/day is rare — when that happens, it usually points to a specific cause (missed doses, absorption interference from food/supplements/other drugs, or a genuine malabsorption issue) rather than simply needing "more." If your dose is unusually high and your TSH still isn't stabilizing, that's worth an explicit conversation with your prescriber about timing and interactions before assuming the dose itself is the problem.
Levothyroxine vs. liothyronine (T3) and natural desiccated thyroid
A comparison most levothyroxine pages skip, despite real search demand for it.
Levothyroxine (Synthroid)
- Hormone
- Synthetic T4 only — your body converts what T3 it needs
- Dosing
- Once daily; long half-life makes levels stable and forgiving of an occasional missed dose
- Guideline status
- Recommended first-line by the American Thyroid Association for most patients
NDT (Armour Thyroid) / liothyronine (T3)
- Hormone
- NDT: fixed-ratio T4+T3 from pig thyroid. Liothyronine: synthetic T3 alone
- Dosing
- Shorter T3 half-life means less stable levels and often multiple daily doses
- Guideline status
- Not first-line; considered when standard levothyroxine hasn't resolved symptoms, under specialist guidance
Some patients report feeling better on NDT or a T4/T3 combination despite normal TSH on levothyroxine alone, and this is a genuine, actively studied area — but current evidence hasn't shown a consistent advantage across the broader patient population, which is why guidelines still favor starting with levothyroxine alone and treating a switch as a deliberate, monitored decision rather than a default.
The boxed warning: not for weight loss
Thyroid hormones, including Synthroid, should not be used for the treatment of obesity or for weight loss — alone or combined with other drugs. In someone with a normal, healthy thyroid (euthyroid), doses within a normal hormonal range simply don't cause weight loss. Larger, supratherapeutic doses can produce serious, even life-threatening toxicity, particularly when combined with stimulant-type weight-loss drugs. This is the FDA's strongest level of warning, and it exists because this exact misuse pattern — taking thyroid hormone specifically to lose weight — has caused real harm.
This matters because "does levothyroxine cause weight gain or loss" is one of the most common questions about this drug, and the honest answer is that weight change on levothyroxine is almost always a signal your dose needs adjustment, not something to chase by over- or under-dosing intentionally. Untreated hypothyroidism itself commonly causes weight gain through a slowed metabolism — treating it correctly typically normalizes weight over time, but taking more than your prescribed dose to accelerate that is exactly what this warning addresses.
Side effects — and signs your dose is wrong
At a correctly titrated dose, most patients on levothyroxine have no side effects at all — because it's replacing a hormone your body should already have, not adding something foreign. The FDA-listed adverse reactions are almost entirely signs of an incorrect dose, in either direction:
Fatigue, weight gain, cold intolerance, constipation, dry skin, depression, and a TSH that remains elevated on lab work.
Palpitations or rapid heartbeat, tremor, anxiety or irritability, insomnia, heat intolerance, excessive sweating, unintended weight loss, and diarrhea — the FDA label lists these as adverse reactions of therapeutic overdosage specifically.
Cardiac risk in older adults or existing heart disease — overtreatment can trigger atrial fibrillation or worsen angina, which is why these patients start at a lower dose. Bone density — sustained over-replacement can increase bone resorption and lower bone mineral density; the lowest effective dose is used for this reason. Worsened diabetes control — starting, changing, or stopping levothyroxine can affect insulin or antidiabetic drug requirements and needs monitoring. Adrenal crisis — in patients with untreated adrenal insufficiency, thyroid hormone must not be started before the adrenal condition is treated. Not for myxedema coma — that medical emergency requires IV treatment, not oral tablets.
Drug interactions and the biotin lab-test trap
Levothyroxine has an unusually long interaction list because so many things affect either its absorption or how your body processes it.
| Interacting drug/substance | What can happen |
|---|---|
| Calcium, iron, antacids, sucralfate, PPIs | Reduce absorption — separate dosing by at least 4 hours |
| Bile acid sequestrants (cholestyramine, colesevelam) | Bind levothyroxine directly, reducing absorption |
| Estrogen, oral contraceptives | Can increase thyroid-binding globulin, changing lab values and sometimes requiring a dose adjustment |
| Warfarin and other oral anticoagulants | Levothyroxine can increase anticoagulant effect — closer monitoring needed |
| Digoxin | Levothyroxine may reduce digoxin's effect as a patient becomes euthyroid |
| Phenytoin, carbamazepine, phenobarbital, rifampin | Can lower thyroid hormone levels by increasing its breakdown or altering protein binding |
| Tricyclic/tetracyclic antidepressants | Can intensify both drugs' effects, including cardiac risk |
| Biotin supplements | Doesn't affect the drug, but distorts TSH/T4 lab results — stop at least 2 days before testing |
This list isn't exhaustive, and several interactions here are about lab-result accuracy as much as drug effect — both matter for getting your dose right. Bring your full medication and supplement list, including anything over-the-counter, to your Arrow Pharmacy pharmacist so we can flag anything that needs spacing out from your levothyroxine dose.
Pregnancy and other populations needing extra monitoring
Levothyroxine is one of the relatively few medications where the clear guidance is to continue, not pause, during pregnancy. Untreated maternal hypothyroidism is linked to real risks — including preeclampsia, miscarriage, and effects on the baby's neurological development — while treated, monitored hypothyroidism generally is not associated with those outcomes. Thyroid hormone requirements commonly rise during pregnancy, so expect more frequent TSH checks and likely a dose increase; the FDA label notes the dose should typically return to your pre-pregnancy level right after delivery. Never stop or adjust your dose on your own — call your prescriber as soon as you know you're pregnant if you're on levothyroxine.
Levothyroxine also passes into breast milk in small amounts, but adequate treatment during lactation hasn't been linked to adverse effects in breastfed infants and can help normalize milk supply in hypothyroid mothers — this isn't a reason to avoid breastfeeding while on levothyroxine.
Buying levothyroxine: prescription, pricing, and savings
Levothyroxine is prescription-only in every US form, but as one of the most commonly filled medications in the country, it's also one of the least expensive generics available.
- Generic is the default, and it's inexpensive. Generic levothyroxine typically costs a small fraction of brand-name Synthroid's cash price — see the price table above, and ask your Arrow Pharmacy pharmacist for a current quote.
- Ask about AbbVie's direct Synthroid program. If you specifically need brand Synthroid (some patients do, for consistency reasons discussed above), the manufacturer's cash-pay "Synthroid Delivers" program has offered a flat price well below typical uninsured retail cost — worth asking us about before assuming insurance is cheaper.
- Discount cards can beat insurance copays for cash-paying or high-deductible patients — ask us to check both before deciding.
- A prescription doesn't require an endocrinologist. Primary care providers routinely diagnose and manage straightforward hypothyroidism; referral to endocrinology is more common for complex cases, pregnancy, or when standard treatment isn't resolving symptoms.
- We can fill or transfer a prescription quickly — and if manufacturer consistency matters to you, ask us to try to keep you on the same generic manufacturer at each refill. Call us at (860) 522-9289.
If cost is a barrier, ask us about patient assistance programs — see our patient assistance programs page for options that apply broadly, not just to this drug.
No active shortage reported — No shortage records found for this generic name.
FDA openFDA — Updated 2026-09-10National Average Drug Acquisition Cost (NADAC): $0.057 per tablet (LEVOTHYROXINE 100 MCG TABLET). This is the average price pharmacies pay wholesalers — not your out-of-pocket cost — published by CMS for pricing transparency.
CMS NADAC — Updated 2026-09-10Levothyroxine (Synthroid) Prices in the USA
| Dosage | Brand-name avg. price | Generic avg. price |
|---|---|---|
| 30-day supply, any standard strength (25–300mcg tablet) | $25–75 (Synthroid) | $8–25 |
| 90-day supply, any standard strength | $70–180 (Synthroid) | $15–45 |
Frequently asked questions
Is Synthroid the same as levothyroxine?
Yes. Levothyroxine is the generic (active-ingredient) name, and Synthroid is the leading brand-name version, made by AbbVie — the same relationship as ibuprofen and Advil. Other brand names for the identical active ingredient include Levoxyl, Tirosint, Unithroid, and Levothroid. All are synthetic forms of T4, the same hormone your thyroid naturally produces.
Is levothyroxine a controlled substance?
No. Levothyroxine does not appear on any DEA controlled-substance schedule. It has no abuse or diversion potential — it does not produce euphoria or any psychoactive effect at a correct dose — which is why it is not restricted the way opioids or benzodiazepines are. It is, however, prescription-only in every form sold in the US.
Can I buy levothyroxine or thyroid medication over the counter?
No — real thyroid hormone requires a prescription in the United States. "OTC thyroid support" supplements exist, but they are not the same thing, and some are genuinely risky: independent lab testing of over-the-counter thyroid supplements has repeatedly found undisclosed, inconsistent amounts of actual thyroid hormone (T3/T4) in products that don't list it as an ingredient — meaning you have no way to know how much hormone you're actually taking. The FDA has separately warned about unapproved animal-derived thyroid products for similar purity and dosing-consistency concerns. If you need thyroid hormone, get it prescribed and dispensed through a licensed pharmacy, not a supplement aisle.
Why does it matter if my pharmacy switches my levothyroxine manufacturer?
Levothyroxine is classified by the FDA as a narrow therapeutic index (NTI) drug — meaning the difference between a dose that works well and one that under- or over-treats you is relatively small. The FDA holds generic levothyroxine to a tighter bioequivalence standard than most generics specifically because of this. Recent FDA-sponsored research suggests switching between well-regulated generic manufacturers doesn't meaningfully change outcomes for most patients, but many endocrinologists still recommend staying on the same manufacturer's product consistently when possible, since pharmacies can switch generic suppliers between refills without you necessarily noticing. If you suspect a refill looks or feels different, ask your pharmacist directly, and get your TSH rechecked about 6 weeks after any confirmed change.
Does levothyroxine cause weight gain or weight loss?
Neither, when your dose is correct. Weight change on this medication is usually a signal that your dose is wrong, not a direct drug effect: untreated or under-treated hypothyroidism commonly causes weight gain (slowed metabolism), while an excessive dose can cause weight loss alongside other symptoms of overtreatment (see the FDA boxed warning below). Taking extra levothyroxine specifically to try to lose weight is explicitly what the FDA's boxed warning addresses — it doesn't work at a normal dose, and higher doses can be genuinely dangerous, particularly for your heart.
How long does it take for levothyroxine to start working?
Longer than most medications — the FDA label notes peak therapeutic effect may not be reached for 4 to 6 weeks at a given dose. That's why your prescriber won't usually recheck your TSH and adjust your dose any sooner than that after starting or changing levothyroxine; testing earlier wouldn't reflect where your levels will actually settle. Some symptom improvement (energy, mood) can happen sooner, but full effect takes the full window.
Can I drink coffee after taking levothyroxine?
Not right away. Multiple studies, including research published by the American Thyroid Association, have found that coffee (and tea) taken close to a levothyroxine dose can meaningfully reduce how much of the drug your body actually absorbs — one commonly cited study found roughly a 27–36% reduction when coffee was taken at the same time or shortly after. The safest approach is what most endocrinologists already recommend for food generally: wait at least 30–60 minutes after your dose before coffee, and ideally longer if your TSH has been hard to stabilize.
Can I take levothyroxine while pregnant?
Yes — and you generally should continue it. Unlike most medications, levothyroxine is specifically something you should not stop during pregnancy: untreated hypothyroidism in pregnancy is linked to real risks including preeclampsia, miscarriage, and effects on the baby's neurological development, while treated, well-monitored hypothyroidism generally is not. Thyroid hormone needs commonly increase during pregnancy, so expect more frequent TSH monitoring and likely a dose increase — never adjust the dose yourself without your prescriber's guidance.
What happens if I miss a dose of levothyroxine?
Take it as soon as you remember that same day; if you don't remember until the next day, just take your normal dose then — don't double up. Because levothyroxine has a long half-life (about a week) and works cumulatively, missing a single dose occasionally has minimal effect on most patients. Missing many doses in a row, on the other hand, can let hypothyroid symptoms return gradually over days to weeks.
Why do I have to take it on an empty stomach?
Food, coffee, and several common supplements (calcium, iron) can all bind to levothyroxine in your gut or otherwise interfere with how much of it actually gets absorbed — the FDA label specifically calls for dosing on an empty stomach, 30–60 minutes before breakfast, and at least 4 hours apart from interfering drugs or supplements. Taking it inconsistently around meals is one of the most common, fixable reasons a patient's TSH won't stabilize despite an otherwise correct dose.
What's the difference between levothyroxine and Armour Thyroid or liothyronine?
Levothyroxine (Synthroid) is synthetic T4 only, matching what your thyroid naturally produces predominantly; liothyronine is synthetic T3, the more active thyroid hormone your body converts T4 into as needed; Armour Thyroid and other "natural desiccated thyroid" (NDT) products are derived from pig thyroid gland and contain a fixed mix of both T4 and T3. Levothyroxine alone is the standard first-line treatment recommended by the American Thyroid Association for most patients because your body regulates its own T4-to-T3 conversion; NDT and T4/T3 combinations are considered case-by-case, generally after standard therapy hasn't resolved symptoms. See the comparison below.
Is 100 mcg (or any specific dose) of levothyroxine a "high dose"?
There's no single universal cutoff — what matters is whether that dose is correct for you, based on your weight, age, cardiac status, and lab results, not the number on the bottle by itself. As a general reference, full adult replacement dosing is calculated at roughly 1.6 mcg per kg of body weight per day, so 100 mcg is a fairly typical maintenance dose for an average-sized adult, not an unusually high one — but only your prescriber, using your actual labs, can say whether your specific dose is right.
Sources
- SYNTHROID (levothyroxine sodium) — FDA-approved prescribing information (label) — U.S. Food and Drug Administration
- NADAC (National Average Drug Acquisition Cost) — LEVOTHYROXINE 100 MCG TABLET — CMS
- openFDA Drug Shortages — U.S. FDA
- Hypothyroidism — Definition & Facts — National Institute of Diabetes and Digestive and Kidney Diseases (NIH)
- Coffee and Levothyroxine Absorption — American Thyroid Association
- Real-World Case Study of Levothyroxine Use and Generic Switching — U.S. FDA (CDER)
- Controlled Substances List — U.S. DEA Diversion Control Division
- Levothyroxine / Synthroid price data (average retail cash price) — GoodRx (consumer price reference)