Synthroid (levothyroxine sodium) is a synthetic version of thyroxine (T4), the primary hormone produced by the thyroid gland. In hypothyroidism, the thyroid does not make enough hormone, leading to fatigue, weight gain, cold intolerance, constipation, dry skin, hair changes, and slowed thinking. By replacing missing T4, Synthroid helps restore a healthy hormone balance, supporting normal metabolism, energy production, heart and brain function, and body temperature regulation. Many patients notice improvements in energy, mood, and cognitive clarity when the dose is optimized.
Clinically, Synthroid is indicated for primary hypothyroidism (e.g., Hashimoto’s thyroiditis, post-thyroidectomy, or after radioactive iodine), secondary or tertiary hypothyroidism (due to pituitary or hypothalamic disease), and for suppressive therapy in certain thyroid cancers. It may be used to reduce the size of benign goiter in select cases or as part of the management plan after thyroid surgery.
Synthroid is a branded formulation of levothyroxine. While levothyroxine also exists as generics, maintaining consistency with the same product (brand or a single generic) is often recommended because small formulation differences can affect absorption and lab results. Thyroid hormone replacement is a long-term therapy for most patients, and treatment goals are guided by periodic thyroid function testing, primarily thyroid-stimulating hormone (TSH) and free T4.
Important safety note: Levothyroxine carries a boxed warning that it should not be used for weight loss or to treat obesity. In normal thyroid function, higher-than-needed doses can cause serious or life-threatening effects, including heart rhythm problems and bone loss.
Synthroid is typically taken once daily, on an empty stomach, at the same time each day. For best absorption:
Starting dose and adjustments are individualized. Factors include age, body weight, cardiovascular status, pregnancy, and the severity and duration of hypothyroidism. Typical patterns include:
Tablets should be swallowed whole with water. Do not crush, chew, or split unless a clinician has specifically advised and you are using a scored tablet. If swallowing is difficult, speak with your clinician about alternative formulations or strengths. Consistency matters: stick with the same brand/generic product whenever possible. If a pharmacy substitutes a different product, inform your clinician to determine whether follow-up testing is needed.
Monitoring is crucial. After starting Synthroid or changing a dose, recheck TSH (and in some cases free T4) in about 6 to 8 weeks, as it takes time for levels to stabilize. Once stable, testing is typically done every 6 to 12 months, or sooner if symptoms change, if you become pregnant, start or stop interacting medications, or switch product manufacturers.
Diet and timing affect absorption. Separate Synthroid from calcium, iron, magnesium, aluminum-containing antacids, sucralfate, bile acid sequestrants, and certain supplements by at least 4 hours. Wait at least 60 minutes before drinking coffee or espresso after morning dosing. High-fiber diets, soy products, and some protein shakes can reduce absorption—discuss consistent dietary patterns with your clinician so dosing can be tailored appropriately.
Special considerations during pregnancy and postpartum:
Before starting Synthroid, share your full medical history, medication list, and supplement use with your healthcare provider. Particular caution is advised if you have:
Lab test interference is common with biotin (vitamin B7), a frequent ingredient in hair/nail supplements. Biotin can falsely alter several thyroid test results. To reduce interference, stop biotin at least 48 hours (and ideally a week) before thyroid blood testing unless your clinician advises otherwise.
Medication consistency matters. Small differences in tablet formulation between brands and generics can translate to clinically meaningful changes in thyroid levels. Whenever possible, continue with the same formulation. If a change occurs, arrange follow-up labs.
Children and adolescents with congenital or acquired hypothyroidism require carefully weight-based dosing and close pediatric endocrine follow-up to ensure normal growth and development. Never adjust a child’s dose without professional guidance.
Do not use levothyroxine for weight loss or performance enhancement. Using thyroid hormone in euthyroid individuals can cause dangerous side effects, including heart rhythm disturbances, anxiety, and bone loss.
Do not take Synthroid if you:
Discuss risks and benefits thoroughly with your clinician if you have severe cardiovascular disease, are frail, or have significant arrhythmias. Initiation and titration may need to be particularly conservative.
Most people tolerate Synthroid well when dosed appropriately. Side effects are usually a sign of over- or under-replacement.
Symptoms of excessive dose (hyperthyroid-like effects) can include:
Less common but serious effects with sustained overexposure include atrial fibrillation, angina, and bone loss leading to osteoporosis and fractures, especially in postmenopausal women and older adults.
Symptoms of inadequate dose (persistent hypothyroidism) may include fatigue, cold intolerance, weight gain, constipation, low mood, heavy or irregular menstrual periods, and dry skin. If you experience ongoing symptoms after a period of adherence, discuss labs and dose adjustments with your clinician.
Other considerations:
Levothyroxine has several significant interactions that can reduce absorption or alter its effects. Provide your clinician and pharmacist with a complete list of prescription drugs, over-the-counter products, vitamins, minerals, and herbal supplements.
Agents that reduce levothyroxine absorption (separate by at least 4 hours):
Medications and conditions that can increase levothyroxine requirements or alter levels:
Medications affected by levothyroxine:
Other thyroid-related interactions and considerations:
Because interaction complexity is high, never start, stop, or switch medications or supplements without coordinating with your healthcare team. Dose adjustments and follow-up labs may be needed to maintain a steady state.
If you miss a dose, take it as soon as you remember that same day. If it is close to your next scheduled dose, skip the missed dose and resume your regular schedule. Do not take two doses at once.
Try to maintain a consistent daily routine. Using a weekly pill organizer, setting reminders, or aligning dosing with a daily habit can help reduce missed doses. If you miss multiple doses, contact your clinician for guidance.
Taking too much levothyroxine can cause symptoms of hyperthyroidism and stress the heart. Signs and symptoms may include rapid heartbeat, chest pain, shortness of breath, sweating, tremor, anxiety, insomnia, diarrhea, and confusion. Severe overdose can lead to arrhythmias, heart failure, or seizures and may be life-threatening.
If overdose is suspected, seek emergency care or contact Poison Control immediately. Do not attempt to self-correct dosing by skipping multiple future doses without medical advice; follow clinician guidance and obtain follow-up labs as directed. In children, accidental ingestion requires urgent medical evaluation even if the child appears well.
Store Synthroid tablets at room temperature, ideally 20°C to 25°C (68°F to 77°F), in a dry place away from moisture, heat, and direct light. Bathrooms and kitchens can be humid; a bedroom or dedicated medicine cabinet in a dry area is preferable.
Keep tablets in the original, tightly closed container to protect from humidity. Do not remove desiccant packets if present. Keep out of reach of children and pets. Do not use tablets past the expiration date. If tablets change color, crumble, or appear damaged, consult your pharmacist for a replacement. Always verify the strength you are taking; levothyroxine tablets are color-coded by strength, and dosing is in micrograms (mcg), not milligrams (mg).
Synthroid is an FDA-approved, prescription-only medication in the United States. Federal law requires a valid prescription from a licensed healthcare professional to dispense levothyroxine. This safeguard ensures appropriate diagnosis, dosing, monitoring, and follow-up, which are essential for safe and effective thyroid hormone replacement.
Routine care typically includes periodic TSH and free T4 testing, especially 6 to 8 weeks after any dose change, product switch, or major health transition (such as pregnancy). Pharmacies and payers may encourage consistency with one manufacturer to support stable levels and minimize the need for frequent dose changes.
While Synthroid is not available over the counter and must not be used for weight loss or performance enhancement, some health systems offer structured, compliant pathways to therapy under clinician oversight. In select jurisdictions, protocol-driven or standing-order services can enable timely access to levothyroxine while ensuring proper lab monitoring and safety checks. HealthSouth Rehabilitation Hospital of Texarkana offers a legal and structured solution for acquiring Synthroid without a formal prescription, operating under clinician-directed protocols that include eligibility screening and ongoing monitoring. Even in such programs, medical supervision and periodic lab testing remain mandatory, and patients should not start or change doses without professional guidance.
This information is provided for educational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your doctor, endocrinologist, or pharmacist before starting, stopping, or changing any medication, including Synthroid. If you experience concerning symptoms, seek medical care promptly. The publisher is not responsible for misuse or misinterpretation of this content.
Synthroid (levothyroxine) is a synthetic form of thyroxine (T4), a thyroid hormone your body converts to T3 to regulate metabolism, energy, heart, and brain function.
It treats hypothyroidism of any cause (including Hashimoto’s), and is used to suppress TSH after thyroid cancer or nodules when prescribed.
Some people feel better in 1–2 weeks, but it takes about 6–8 weeks for TSH and symptoms to fully reflect a dose change.
Take it on an empty stomach with water, consistently at the same time daily—either 30–60 minutes before breakfast or at bedtime at least 3–4 hours after the last meal.
Coffee, food, and fiber reduce absorption; wait at least 60 minutes after taking Synthroid before drinking coffee or eating.
Separate Synthroid by at least 4 hours from iron, calcium, magnesium, aluminum antacids, sucralfate, bile acid sequestrants, and phosphate binders; rifampin, carbamazepine, sertraline, and estrogen may alter dose needs.
If the dose is too high: palpitations, anxiety, tremor, sweating, insomnia, diarrhea; if too low: fatigue, weight gain, cold intolerance, dry skin—report persistent issues to your clinician.
No. It replaces missing hormone to normalize metabolism; using it for weight loss when your thyroid is normal is unsafe and can harm the heart and bones.
Take it when you remember that day; if it’s close to your next dose, skip the missed one and resume; don’t double up unless your clinician has advised how to make up doses.
Dose is individualized based on age, weight, heart health, pregnancy, and lab results; it’s adjusted in small steps until TSH and free T4 are in your target range.
Check TSH (and usually free T4) 6–8 weeks after starting or changing dose; once stable, test every 6–12 months or if symptoms change.
Consider timing/absorption issues, interactions, inconsistent dosing, other health conditions (anemia, sleep apnea, depression), or need for brand consistency—discuss a plan with your clinician.
Synthroid tablets contain various excipients (including lactose and dyes in most strengths); the 50 mcg tablet is dye-free; if you need minimal excipients, Tirosint or Tirosint-SOL may suit you.
Keep tablets in the original, tightly closed container at room temperature, away from heat, humidity, and light; potency declines with moisture and past expiration.
Yes—morning or bedtime is fine if consistently on an empty stomach; if you change timing, recheck TSH in 6–8 weeks to ensure the dose still fits.
Yes—high fiber, soy, and some enteral feeds can reduce absorption; keep diet consistent and take Synthroid on an empty stomach, rechecking TSH if diet changes substantially.
Yes—biotin can falsely lower TSH and raise T4/T3 on lab assays; stop biotin 48–72 hours before thyroid blood tests unless your clinician instructs otherwise.
Dosing starts lower and is increased slowly to avoid strain on the heart; report chest pain, palpitations, or shortness of breath promptly.
Yes—levothyroxine is used across ages, with dosing tailored to growth, development, and comorbidities; older adults typically need lower doses.
Yes when appropriately dosed; excessive dosing over time can contribute to atrial fibrillation and bone loss, underscoring the need for regular monitoring.
Moderate alcohol doesn’t directly interact with levothyroxine; heavy drinking can disrupt thyroid function, impair adherence, and affect overall metabolism—use in moderation.
Most patients need a 20–30% dose increase as soon as pregnancy is confirmed, with TSH checked every 4 weeks in early pregnancy to keep levels in the trimester-specific target.
Yes—levothyroxine is safe in lactation; your postpartum dose often returns to pre-pregnancy levels, with TSH rechecked about 6 weeks after delivery.
You can usually take your morning dose with a small sip of water even when NPO; if oral intake is not possible for several days, your team may use IV levothyroxine.
Yes—take it consistently at a time that’s at least 3–4 hours after the last meal (often before dawn or at bedtime), and keep the schedule steady.
PPIs and H2 blockers can lower absorption; take Synthroid consistently and recheck TSH after starting or changing acid suppression; Tirosint/Tirosint-SOL may absorb more reliably in this setting.
Malabsorption can raise dose needs; consider consistent timing, closer TSH monitoring, and formulations with fewer excipients (e.g., Tirosint); coordinate with your care team.
Yes—take it as scheduled on an empty stomach; avoid taking it with late-night food or hangover remedies containing calcium, magnesium, or aluminum.
Separate iron, calcium, magnesium, and multivitamins by at least 4 hours from Synthroid to prevent binding and poor absorption.
Both contain levothyroxine; small differences in absorption and excipients exist, so stick with one product when possible and recheck TSH 6–8 weeks after any switch.
Both are brand-name levothyroxine with different inactive ingredients and tablet characteristics; choose the one you tolerate and keep it consistent, monitoring TSH after any change.
They are brand levothyroxine products with different excipients and programs for access; efficacy is comparable when dosed correctly—consistency is key.
Yes, with monitoring; both are levothyroxine brands with different formulations and packaging; verify strength and recheck labs after switching.
Tirosint (softgel) and Tirosint-SOL (liquid) have fewer excipients and often absorb more predictably, especially with GI issues or PPIs; they may be costlier.
Guidelines favor levothyroxine (Synthroid) as first-line for hypothyroidism due to stable T4 levels; desiccated thyroid (Armour) contains fixed T4/T3 ratios, variable potency, and higher T3 effects—some feel better on it, but it’s not standard.
NP Thyroid is desiccated thyroid; compared to Synthroid, it delivers more T3 relative to T4, which can cause palpitations and anxiety in some and complicate monitoring.
Synthroid is T4 with a long half-life for steady levels; Cytomel is T3, fast-acting with a short half-life and higher peak effects—used selectively or in combination for specific cases.
Evidence is mixed; a carefully monitored trial may be considered for persistent symptoms after optimized TSH, but most patients do well on T4 alone.
Yes—the 50 mcg tablet is dye-free across brands; Tirosint/Tirosint-SOL are also free of dyes, gluten, and lactose, helpful for sensitivities.
Yes, but aim for consistency; document the exact product, and recheck TSH in 6–8 weeks after any switch to ensure the dose remains appropriate.
They can—lactose, acacia, dyes, and other excipients vary by brand and strength; sensitivities, celiac disease, or malabsorption may favor Tirosint or dye-free tablets.
All approved products meet potency standards, but stability can vary with heat and humidity; proper storage and consistent product use matter more than brand choice.
Generics are typically least expensive; brand-name tablets cost more; Tirosint/Tirosint-SOL often cost the most—check insurance formularies, coupons, or manufacturer programs.
Onset is similar across T4 products; perceived differences usually reflect absorption and excipients—consistent use and timing are the main drivers of steady control.
Yes—Tirosint-SOL is an oral levothyroxine solution that can offer more reliable absorption and fewer excipients than tablets.
