Levothyroxine Side Effects and Safety: What the FDA Record Shows

Levothyroxine Side Effects are documented on the FDA prescribing label, and reported separately by patients and doctors to the FDA’s adverse event system. This page sets out what the official record actually says about Levothyroxine: what it is approved to treat, what the label warns about, its recall history, and what the reported side effects are — along with what those figures do and do not mean.

What Levothyroxine Is Prescribed For, and Where Levothyroxine Side Effects Come From

According to the FDA label, ypothyroidism Levothyroxine sodium tablets are 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 Levothyroxine sodium tablets are indicated in adult and pediatric patients, including neonates, as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer. […]

Two separate official sources describe levothyroxine side effects. The prescribing label records what was observed in clinical trials, where the drug was compared against a control group. The FDA’s adverse event database records what patients and clinicians have reported since approval, which is a much larger but far less controlled picture. Both appear below, and they answer different questions.

The FDA has revised this label recently. The label’s own record of recent major changes reads: Dosage and Administration, Important Considerations for Dosing ( 2.2 ) 2/2024 Dosage and Administration, Monitoring TSH and/or Thyroxine (T4) Levels ( 2.4 ) 2/2024 A recent revision usually means new safety information was added.

The FDA Boxed Warning on Levothyroxine

A boxed warning is the most serious warning the FDA requires on a prescription label. It does not mean the medicine should not be used. It means there is a specific risk serious enough that the FDA requires it to appear at the very top of the prescribing information, so that prescribers weigh it deliberately for each patient.

Prescribers see this warning every time they consult the label. If it concerns you, it is a reasonable thing to raise at your next appointment and ask how it applies to your own situation.

Warnings Beyond the Common Levothyroxine Side Effects

The label’s warnings and precautions section describes risks the FDA requires prescribers to weigh. For Levothyroxine it covers: erious risks related to overtreatment or undertreatment with levothyroxine sodium tablets: Titrate the dose of levothyroxine sodium carefully and monitor response to titration. (5.1) Cardiac adverse reactions in the elderly and in patients with underlying cardiovascular disease: Initiate levothyroxine sodium at less than the full replacement dose because of the increased risk of cardiac adverse reactions, including atrial fibrillation.

(2.3 , 5.2 , 8.5) Myxedema coma: Do not use oral thyroid hormone drug products to treat myxedema coma. (5.3) Acute adrenal crisis in patients with concomitant adrenal insufficiency: Treat with replacement glucocorticoids prior to initiation of levothyroxine sodium treatment. (5.4) Worsening of diabetic control: Therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control after starting, changing, or discontinuing thyroid hormone therapy. […]

These are the risks the FDA has judged significant enough to state formally, and they sit apart from the routine levothyroxine side effects most people ask about. They apply to different patients to very different degrees, which is why the same medicine can be routine for one person and unsuitable for another.

Levothyroxine Side Effects Listed on the FDA Label

The label’s adverse reactions section records what was observed in clinical trials: dverse reactions associated with levothyroxine sodium therapy are primarily those of hyperthyroidism due to therapeutic overdosage [see Warnings and Precautions (5) and Overdosage (10) ]. They include the following: General: fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating Central nervous system: headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia Musculoskeletal: tremors, muscle weakness, muscle spasm Cardiovascular: palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest Respiratory: dyspnea Gastrointestinal: diarrhea, vomiting, abdominal cramps, elevations in liver function tests Dermatologic: hair loss, flushing, rash Endocrine: decreased bone mineral density Reproductive: menstrual irregularities, impaired fertility Seizures have […]

Trial data is the most reliable source for how common levothyroxine side effects are, because the people taking the drug were compared against people who were not. A symptom that appeared just as often in the control group is not caused by the medicine.

Reported Levothyroxine Side Effects in the FDA Database

Who the Label Says Should Take Extra Care

Contraindications. The label states that Levothyroxine should not be used in certain situations: evothyroxine sodium tablets are contraindicated in patients with uncorrected adrenal insufficiency [see Warnings and Precautions (5.4) ]. Uncorrected adrenal insufficiency. (4)

Interactions with other medicines. ee full prescribing information for drugs that affect thyroid hormone pharmacokinetics and metabolism (e.g., absorption, synthesis, secretion, catabolism, protein binding, and target tissue response) and may alter the therapeutic response to levothyroxine sodium. […]

Older adults. 8.5 Geriatric Use Because of the increased prevalence of cardiovascular disease among the elderly, initiate levothyroxine sodium at less than the full replacement dose [see Dosage and Administration (2.3) and Warnings and Precautions (5.2) ] . Atrial arrhythmias can occur in elderly patients. Atrial fibrillation is the most common of the arrhythmias observed with levothyroxine overtreatment in the elderly.

Your pharmacist can check your full medicine list against this in a couple of minutes, including anything bought over the counter, and that check is free.

Levothyroxine Recall History

The FDA enforcement database records 96 recall entries involving Levothyroxine products (10 Class I, 84 Class II, 2 Class III). A recall almost always concerns specific manufactured batches rather than the medicine itself, and different manufacturers of the same generic drug have separate recall records.

The FDA classifies recalls by how serious the potential consequence is. Class I means a reasonable probability of serious harm or death; Class II means temporary or reversible harm is possible; Class III means the product breaks a regulation but is unlikely to cause harm.

If a batch you have was recalled, the pharmacy that dispensed it is the fastest way to find out and to get a replacement. Do not simply stop taking a prescribed medicine because a recall notice exists — the recall may not affect your batch, and stopping can carry its own risk.

Is Levothyroxine the Subject of Litigation?

We are not tracking consolidated federal litigation over Levothyroxine. It is a widely prescribed medicine, and the information on this page is drawn from the FDA label and public safety data rather than from any legal claim.

If You Are Worried About Levothyroxine Side Effects

Concern about levothyroxine side effects is a good reason to have a conversation, and not a reason to act alone. Do not stop taking a prescribed medicine, or change how you take it, because of anything you read here. Talk to the prescriber or pharmacist who knows your medical history first. Stopping some medicines abruptly carries risks of its own, and your prescriber can tell you whether that applies to yours.

Write down what you have noticed and when it started before the appointment. Not everything that happens while taking a medicine is one of its levothyroxine side effects, and a specific account — what changed, when, and how often — is what lets a clinician tell the difference.

You can also report a side effect directly to the FDA through MedWatch. Reports from patients are part of how safety signals are detected, and filing one takes a few minutes.

Frequently Asked Questions

What are the most commonly reported levothyroxine side effects?

In FDA reports, the most frequently mentioned are fatigue, nausea, headache. The label’s own adverse reactions section, drawn from clinical trials, is the better guide to how common a side effect actually is, because reports to the FDA are not collected in a way that supports rates.

Has Levothyroxine been recalled?

There are 96 recall records for Levothyroxine products, the most recent dated 2026-07-08. Recalls generally affect specific manufactured batches rather than the medicine as a whole. Your pharmacy can tell you whether a batch you have was affected.

Does Levothyroxine have a boxed warning?

Yes. The boxed warning is reproduced above. It is the most serious warning the FDA requires, and it exists so that prescribers weigh a specific risk for each patient rather than overlooking it.

Do the FDA report numbers tell me how common these levothyroxine side effects are?

No. Reports are unverified, anyone can file one, and the total mostly reflects how many people take the medicine and how much attention it is getting. A high count is not evidence of danger, and a low one is not evidence of safety. Clinical trial data on the label is the source that supports rates.

Where can I check levothyroxine side effects for the exact product I have?

DailyMed holds the current FDA label for every marketed product, searchable by the name on your packaging. Different manufacturers and formulations of the same medicine can have slightly different labels, so checking the one you actually have is worth the two minutes.

Official Sources

• DailyMed (National Library of Medicine) — the current FDA prescribing label for every product
• FDA Adverse Event Reporting System dashboard — the public report data summarised above
• FDA recalls and safety alerts — current recall notices
• FDA MedWatch — how to report a side effect yourself

Related Guides

• All Drug Safety Profiles
• Drug Safety Explainers
• Product Recalls
• Active Case Pages

Medical and legal disclaimer. This page summarises publicly available FDA data about Levothyroxine and is general information, not medical advice, and not legal advice. It is not a substitute for the judgement of a clinician who knows your medical history. Nothing here states that Levothyroxine caused any illness or injury in any individual. Adverse event reports are unverified and do not establish causation.

FDA labels are revised regularly; confirm current information on DailyMed or with your pharmacist. Do not stop taking a prescribed medicine, or change how you take it, because of anything you read here. Talk to the prescriber or pharmacist who knows your medical history first.