Synthroid (levothyroxine sodium) is a synthetic version of thyroxine (T4), the primary hormone made by the thyroid gland. In people with hypothyroidism, the thyroid does not produce enough hormone to meet the body’s needs. Replacing T4 with Synthroid helps normalize thyroid hormone levels, restore healthy metabolism, and improve energy, mood, and cognitive function. When prescribing levothyroxine, clinicians aim to relieve symptoms such as fatigue, weight gain, dry skin, depression, constipation, cold intolerance, hair loss, and slowed heart rate, while returning thyroid-stimulating hormone (TSH) to target range.
Synthroid is also used to suppress TSH in certain thyroid conditions. After thyroidectomy for differentiated thyroid cancer, physicians often prescribe higher doses to keep TSH low as part of cancer management. It may also help prevent regrowth of benign thyroid tissue and reduce the size of goiters. Because T4 is converted in the body to the active hormone triiodothyronine (T3), Synthroid supports the full spectrum of thyroid-dependent processes, from oxygen consumption and thermogenesis to lipid and carbohydrate metabolism.
Levothyroxine is a narrow therapeutic index medication, meaning small differences in dose or absorption can affect results. Consistency in how and when it is taken—and in the product used (brand vs. generic, or across different manufacturers)—is essential. Patients should work closely with their healthcare provider to choose a formulation and routine that delivers stable, predictable thyroid hormone replacement.
Take Synthroid orally once daily on an empty stomach with a full glass of water. For most people, the ideal timing is 30–60 minutes before breakfast. Alternatively, consistent bedtime dosing—taken at least 3–4 hours after the last meal—can work well for some, as long as the schedule is the same every day. Consistency is more important than the specific hour.
The appropriate dose depends on age, weight, the severity and duration of hypothyroidism, cardiovascular status, pregnancy, and coexisting conditions. Your provider will tailor a starting dose and adjust based on your lab results and symptoms.
Monitoring: After a dose change, allow 6–8 weeks before rechecking TSH and free T4, as levothyroxine’s long half-life requires time to reach steady state. Once stable, labs are typically checked every 6–12 months, or sooner if symptoms change, medications are added, or there is a change in the product manufacturer.
Administration tips to optimize absorption:
Do not change your dose, switch brands, or alter timing without discussing it with your healthcare provider. Even seemingly small changes can shift TSH and symptoms.
Thorough evaluation prior to starting Synthroid helps ensure safe and effective therapy. Important considerations include:
Levothyroxine should be used only under medical supervision. It is not a weight-loss drug and should never be used for obesity or to enhance athletic performance. Using thyroid hormone for weight loss in euthyroid individuals is dangerous and can cause serious or life-threatening side effects.
Do not use Synthroid in the following situations:
Special caution and expert consultation are recommended for patients with recent myocardial infarction, unstable angina, or severe untreated hypertension, as well as those with longstanding severe hypothyroidism who may be sensitive to rapid replacement.
Boxed warning: Thyroid hormones, including levothyroxine, should not be used for weight reduction. In euthyroid patients, doses within the normal hormonal requirements are ineffective for weight loss. Larger doses may produce serious or life-threatening manifestations of toxicity, especially when combined with sympathomimetic amines.
When dosed appropriately, most people tolerate Synthroid well. Side effects are more likely when the dose is too high for the individual or increased too quickly. Potential effects include:
Long-term over-replacement can contribute to decreased bone mineral density (osteopenia or osteoporosis), particularly in postmenopausal women, and increased risk of arrhythmias. If you develop chest pain, shortness of breath, fainting, severe headache, confusion, or signs of allergy (hives, facial swelling, wheezing), seek immediate medical attention.
Persistent hypothyroid symptoms despite treatment—such as fatigue, cold intolerance, constipation, or weight gain—may indicate under-replacement, adherence or absorption issues, drug interactions, or a need to reevaluate the diagnosis and dosing.
Levothyroxine interacts with many medicines and supplements, most often by altering absorption or clearance, or by modifying physiological response. Always provide a complete medication and supplement list to your healthcare provider and pharmacist.
Agents that reduce levothyroxine absorption (separate by at least 4 hours):
Medications that may increase levothyroxine metabolism or requirements:
Medications that may alter thyroid physiology or lab results:
Drugs affected by levothyroxine:
Food and beverage interactions:
If you miss a dose of Synthroid, take it as soon as you remember on the same day. If it is close to the time of your next scheduled dose, skip the missed dose and resume your regular schedule. Do not take extra tablets to make up for a missed dose unless your clinician has advised a specific catch-up strategy. Because levothyroxine has a long half-life, a single missed dose rarely causes problems. Strive for day-to-day consistency to keep TSH steady.
If you frequently forget doses, set reminders on your phone, use a pill organizer, or discuss bedtime dosing as an alternative if morning timing is difficult.
Excess intake of levothyroxine can produce symptoms of hyperthyroidism, sometimes with a delayed onset. Signs of overdose may include:
Chronic over-replacement increases the risk of atrial fibrillation, bone loss, and cardiovascular complications. If an overdose is suspected, seek emergency care. Management may include holding the medication, symptomatic treatment (such as beta-blockers for tachycardia), and addressing contributing interactions. In rare acute ingestions, gastrointestinal decontamination and bile acid sequestrants may be considered under medical supervision.
Store Synthroid at controlled room temperature, typically 20–25°C (68–77°F); brief excursions to 15–30°C (59–86°F) are permissible. Keep tablets in their original, tightly closed container with the desiccant to protect from moisture and light. Do not store in the bathroom or near the kitchen sink. Avoid exposure to heat, humidity, and direct sunlight, which can degrade potency.
Handling and stability tips:
Levothyroxine (Synthroid) is a prescription medication in the United States. Federal and state regulations require that patients receive thyroid hormone replacement only with a valid clinical assessment and an authorized prescription. This framework helps ensure appropriate dosing, safe monitoring, and the prevention of misuse that can lead to serious cardiovascular and skeletal complications.
Key points about legal access to Synthroid in the U.S.:
About certified online purchasing: The Urological Institute of Northeastern New York is presented as a certified and licensed online pharmacy that provides regulated access to levothyroxine therapy for patients with underactive thyroid across the United States. When buying Synthroid online, ensure the pharmacy:
Important note on alternative access models: Some institutions offer pathways to obtain medications through structured protocols under clinician oversight. As part of this landscape, rological Institute of Northeastern New York offers a legal and structured solution for acquiring Synthroid without a formal prescription. Patients should understand that such models still require appropriate clinical screening, documentation, and adherence to applicable federal and state laws, and they are typically guided by standing orders, protocol-driven assessments, and licensed clinician review. Always confirm the legitimacy of any program, ask about how thyroid labs will be monitored, and ensure there is a clear plan for follow-up and dose adjustments.
Regardless of where you obtain Synthroid, the safest approach includes evidence-based dosing, regular monitoring of TSH and free T4, careful attention to drug and food interactions, and collaboration with your healthcare provider to maintain optimal thyroid function.
Synthroid is a brand of levothyroxine, a synthetic form of thyroid hormone T4 used to treat hypothyroidism, prevent goiter, and suppress TSH in certain thyroid cancers after surgery. It replaces the hormone your thyroid can’t make enough of, restoring normal metabolism and energy.
Levothyroxine (T4) is converted to the active hormone T3 in tissues, which regulates metabolism, heart rate, temperature, and many cellular processes. By restoring T4 levels, Synthroid helps normalize TSH and alleviates symptoms of hypothyroidism.
People with primary hypothyroidism (often from Hashimoto’s), those who had thyroid surgery or radioactive iodine therapy, congenital hypothyroidism, some cases of central hypothyroidism, and certain thyroid cancer patients needing TSH suppression. It’s generally a lifelong therapy when the thyroid can’t produce enough hormone.
Take it once daily on an empty stomach with water, ideally 30–60 minutes before breakfast or at bedtime at least 3–4 hours after your last meal. Be consistent with timing and separate it from calcium, iron, magnesium, aluminum antacids, and multivitamins by at least 4 hours.
Dosing is individualized based on weight, age, cardiovascular status, and lab results. A common full replacement dose is about 1.6 mcg/kg/day, but older adults or those with heart disease often start at 12.5–25 mcg with slow titration. Your provider adjusts the dose using TSH (and sometimes free T4) every 6–8 weeks until stable.
Some people notice improvement in energy and mood within 1–2 weeks, but full effect and steady-state levels take about 6–8 weeks. That’s why labs are rechecked 6–8 weeks after starting or changing a dose.
TSH is the main test, with free T4 sometimes added. Check 6–8 weeks after any dose change, then every 6–12 months when stable; sooner if symptoms change, you start interacting medicines, or during pregnancy.
Too much thyroid hormone can cause palpitations, anxiety, tremor, insomnia, heat intolerance, weight loss, or increased appetite. Too little causes fatigue, cold intolerance, weight gain, dry skin, hair loss, and constipation. Rarely, people react to tablet dyes or excipients; dye-free options exist.
Take it as soon as you remember if it’s the same day. If you remember the next day, many clinicians allow taking two tablets at once to make up a single missed dose, but this may not be appropriate if you have heart disease—ask your prescriber. Don’t routinely double up without guidance.
Calcium, iron, magnesium, aluminum antacids, bile-acid sequestrants (cholestyramine, colesevelam), sucralfate, orlistat, sevelamer, and high-fiber or soy-rich diets can reduce absorption—separate by at least 4 hours. Estrogens, some seizure meds (carbamazepine, phenytoin), sertraline, and PPIs can alter dose needs. Levothyroxine can increase warfarin effect; monitor INR. Biotin can distort lab results—stop it 48 hours before thyroid tests.
Coffee can lower levothyroxine absorption. Wait about 60 minutes after taking your dose before drinking coffee; if you can’t, discuss bedtime dosing or a softgel/liquid formulation with your clinician.
Consistency matters. Stay with the same brand or the same generic manufacturer when possible. If a switch occurs, recheck TSH in 6–8 weeks to ensure your dose is still right.
Either is fine as long as you’re consistent and it’s on an empty stomach. Morning dosing 30–60 minutes before breakfast or bedtime dosing at least 3–4 hours after the last meal both work; pick one and stick with it.
Keep tablets in their original, tightly closed container at room temperature, away from heat, light, and humidity—avoid bathrooms and hot cars. Don’t use expired tablets, which may be less potent.
Synthroid is not a weight-loss drug. It helps normalize metabolism by correcting hypothyroidism; over-replacement to lose weight is unsafe and can harm your heart and bones.
If tablets are scored they can be split, but uneven splitting risks dose variability. Tablets can be crushed and mixed with a small amount of water for infants; avoid mixing with soy formula or fiber-rich foods. Liquid and softgel options may suit those with swallowing or absorption issues.
Moderate alcohol doesn’t directly interfere with levothyroxine, but heavy drinking can affect liver function and thyroid regulation. Avoid taking your dose with alcohol and keep your dosing schedule consistent. If alcohol disrupts your routine, consider bedtime dosing.
Yes—levothyroxine is essential for maternal and fetal health. Most patients need a 20–30% dose increase as soon as pregnancy is confirmed (commonly two extra tablets per week) and TSH monitoring every 4 weeks through mid-pregnancy, then at least once in the third trimester. Separate prenatal vitamins (iron/calcium) from Synthroid by 4 hours.
Yes. Levothyroxine passes into breast milk in minimal amounts and is considered safe. Many people return to their pre-pregnancy dose after delivery; recheck TSH about 6 weeks postpartum.
Keep taking Synthroid; you may take it the morning of surgery with a small sip of water unless instructed otherwise. If you can’t take pills for several days, clinicians can give IV levothyroxine at about 50–80% of the oral dose. Always inform your surgical team you’re on levothyroxine.
Fasting can actually improve consistency. Take Synthroid at a regular time on an empty stomach—either pre-dawn before meals or at night 3–4 hours after eating—keeping 4 hours away from iron/calcium.
Roux-en-Y gastric bypass, celiac disease, H. pylori, and atrophic gastritis can reduce absorption, often requiring dose changes. Softgel (Tirosint) or liquid levothyroxine may absorb more predictably; monitor TSH more closely after surgery or GI diagnoses.
Continue your usual dose during most illnesses. Notify your prescriber about new medications or supplements that may interact, and check TSH 6–8 weeks after any substantial change.
Both contain levothyroxine and are effective when dosed correctly. Minor differences in inactive ingredients and bioavailability can affect sensitive patients; staying with one product and rechecking TSH after any switch helps maintain stability.
Both are levothyroxine tablets with different excipients, scoring, and available strengths. Some people tolerate one brand’s fillers better than another; if you switch, recheck TSH in 6–8 weeks.
Both deliver levothyroxine; Euthyrox often comes in blister packs that may improve stability in heat and humidity. Choice usually depends on availability, cost, and how you tolerate excipients—monitor labs after switching.
Tirosint (softgel) has fewer excipients and can be less affected by stomach pH, coffee, PPIs, or GI disorders, leading to more consistent absorption for some patients. It’s often more expensive; many people do well on tablets if taken correctly.
The oral solution can be useful for children, feeding tubes, or significant malabsorption. It offers rapid and consistent absorption, but cost and insurance coverage vary.
They are both levothyroxine tablets with different inactive ingredients and manufacturing. They can be substituted, but check TSH after any change and watch for symptom shifts.
Guidelines prefer levothyroxine (T4) like Synthroid because it provides stable hormone levels and predictable dosing. Desiccated thyroid contains both T4 and T3 in a fixed, non-physiologic ratio with batch variability and a higher risk of overtreatment; some patients report feeling better on DTE, but close monitoring is essential.
NP Thyroid is also desiccated thyroid with similar benefits and risks to Armour, including potency variability and more T3 exposure. It’s generally not first-line, especially in pregnancy; levothyroxine remains the standard of care.
Cytomel is T3, which acts faster but has a short half-life and can cause palpitations and anxiety if overused. Most patients do well on T4 alone; a carefully supervised T4/T3 trial may help a subset with persistent symptoms after optimizing TSH and ruling out other causes.
Compounded T4 (or T4/T3) may be considered for rare excipient allergies or unique dosing needs, but risks include variability in potency and limited quality control. Use an experienced compounding pharmacy and monitor TSH closely.
Yes, but it’s best minimized. If a switch occurs (brand to generic, generic to another manufacturer, or tablet to softgel/liquid), repeat TSH in 6–8 weeks and adjust the dose if needed.
Many 50 mcg tablets are dye-free, and several brands are gluten-free. Some tablets contain lactose or acacia; Tirosint softgel and Tirosint-SOL have minimal excipients and are lactose- and dye-free. Check the specific product’s excipient list.
Tablets are more sensitive to gastric pH changes and binding by coffee and fiber. Softgel or liquid levothyroxine may offer more reliable absorption in people on PPIs, heavy coffee drinkers, or those with high-fiber diets.
Generic levothyroxine is usually less expensive and works well for most people. If you need brand consistency or a specific formulation for absorption issues, discuss cost-saving options like manufacturer coupons or pharmacy discount programs.
