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Levothyrox Side Effects

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Common Levothyrox Side Effects


The most commonly reported Levothyrox side effects (click to view or check a box to report):

Fatigue (216)
Nausea (181)
Headache (180)
Dyspnoea (152)
Dizziness (144)
Asthenia (137)
Product Substitution Issue (133)
Alopecia (131)
Pain (128)
Malaise (128)
Diarrhoea (128)
Blood Thyroid Stimulating Hormone Increased (121)
Pruritus (111)
Vomiting (107)
Anxiety (105)
Insomnia (101)
Hypothyroidism (100)
Arthralgia (95)
Weight Increased (94)
Feeling Abnormal (91)

➢ More



If you or someone in your family has experienced a serious side effect to a health product, you are encouraged to report the experience to your health care professional (e.g. physician, pharmacist). You could also complete a copy of the side effect reporting form or report your side effect to FDA.

Levothyrox Side Effects Reported to FDA



Levothyrox Side Effect Report#9995717
Alopecia, Urticaria, Product Substitution Issue
This is a report of a 34-year-old female patient (weight: NA) from US, suffering from the following health symptoms/conditions: NA, who was treated with Levothyroxine 0.075 Mg (75 Mcg) Tabs (dosage: NA, start time:
Feb 01, 2014), combined with:
  • Aspirin
and developed a serious reaction and side effect(s): Alopecia, Urticaria, Product Substitution Issue after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Levothyroxine 0.075 Mg (75 Mcg) Tabs treatment in female patients, resulting in Alopecia side effect.
Levothyrox Side Effect Report#9995657
Pulmonary Embolism, Thyroiditis, Malaise, Syncope, Platelet Count Decreased, Tachycardia, Dilatation Ventricular, Deep Vein Thrombosis, Deep Vein Thrombosis
This report suggests a potential Levothyrox Pulmonary Embolism side effect(s) that can have serious consequences. A 20-year-old female patient (weight: NA) from FR was diagnosed with the following symptoms/conditions: thyroiditis,contraception and used Levothyrox (dosage: NA) starting 200811. After starting Levothyrox the patient began experiencing various side effects, including: Pulmonary Embolism, Thyroiditis, Malaise, Syncope, Platelet Count Decreased, Tachycardia, Dilatation Ventricular, Deep Vein Thrombosis, Deep Vein ThrombosisAdditional drugs used concurrently:
  • Adepal
  • Propranolol (propranolol) (propranolol)
The patient was hospitalized. Although Levothyrox demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Pulmonary Embolism, may still occur.
Levothyrox Side Effect Report#9995643
Hypophosphataemia, Hypothyroidism, Condition Aggravated, Depression, Vitamin D Deficiency
This Hypophosphataemia problem was reported by a health professional from NL. A 47-year-old female patient (weight: NA) was diagnosed with the following symptoms/conditions: hypothyroidism,anaemia. On NS this consumer started treatment with Levothyroxine (dosage: NA). The following drugs were being taken at the same time:
  • Ferric Carboxymaltose
When using Levothyroxine, the patient experienced the following unwanted symptoms/side effects: Hypophosphataemia, Hypothyroidism, Condition Aggravated, Depression, Vitamin D DeficiencyThe patient was hospitalized.Although all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Hypophosphataemia, may become evident only after a product is in use by the general population.
Levothyrox Side Effect Report#9995361
Palpitations, Asthenia, Hypoaesthesia, Dizziness
This Palpitations side effect was reported by a consumer or non-health professional from US. A 39-year-old female patient (weight:NA) experienced the following symptoms/conditions: NA.The patient was prescribed Levothyroxine (drug dosage: NA), which was initiated on
Jan 15, 2014. Concurrently used drugs: NA..After starting to take Levothyroxine the consumer reported adverse symptoms, such as: Palpitations, Asthenia, Hypoaesthesia, DizzinessThese side effects may potentially be related to Levothyroxine.
Levothyrox Side Effect Report#9994663
Decreased Appetite, Asthenia, Weight Decreased, Anhedonia, Ageusia, Hyperthyroidism, Atrial Fibrillation
This is a report of a 76-year-old male patient (weight: NA) from US, suffering from the following health symptoms/conditions: hypothyroidism, who was treated with Levothyroxine (dosage: NA, start time:
Mar 05, 2012), combined with: NA. and developed a serious reaction and side effect(s): Decreased Appetite, Asthenia, Weight Decreased, Anhedonia, Ageusia, Hyperthyroidism, Atrial Fibrillation after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Levothyroxine treatment in male patients, resulting in Decreased Appetite side effect. The patient was hospitalized.
Levothyrox Side Effect Report#9980046
Blood Thyroid Stimulating Hormone Increased
This report suggests a potential Levothyroxine Blood Thyroid Stimulating Hormone Increased side effect(s) that can have serious consequences. A female patient (weight: NA) from US was diagnosed with the following symptoms/conditions: hypothyroidism and used Levothyroxine (dosage: NA) starting
Jan 09, 2014. After starting Levothyroxine the patient began experiencing various side effects, including: Blood Thyroid Stimulating Hormone IncreasedAdditional drugs used concurrently: NA. Although Levothyroxine demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Blood Thyroid Stimulating Hormone Increased, may still occur.
Levothyrox Side Effect Report#9970204
Angioedema, Ear Pain, Stress, Hypersensitivity
This Angioedema problem was reported by a consumer or non-health professional from US. A 66-year-old female patient (weight: NA) was diagnosed with the following symptoms/conditions: hypothyroidism,hypertension. On NS this consumer started treatment with Levothyrox (dosage: NA). The following drugs were being taken at the same time:
  • Bisoprolol
When using Levothyrox, the patient experienced the following unwanted symptoms/side effects: Angioedema, Ear Pain, Stress, HypersensitivityAlthough all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Angioedema, may become evident only after a product is in use by the general population.
Levothyrox Side Effect Report#9970193
Abortion Spontaneous, Maternal Exposure During Pregnancy
This Abortion Spontaneous side effect was reported by a consumer or non-health professional from RS. A 32-year-old female patient (weight:NA) experienced the following symptoms/conditions: hypothyroidism.The patient was prescribed Levothyroxine (levothyroxine) (levothyroxine Sodium) (drug dosage: NA), which was initiated on NS. Concurrently used drugs: NA..After starting to take Levothyroxine (levothyroxine) (levothyroxine Sodium) the consumer reported adverse symptoms, such as: Abortion Spontaneous, Maternal Exposure During PregnancyThese side effects may potentially be related to Levothyroxine (levothyroxine) (levothyroxine Sodium).
Levothyrox Side Effect Report#9970171
Caesarean Section, Nausea, Pre-eclampsia, Headache, Maternal Exposure During Pregnancy, Induced Labour, Foetal Heart Rate Abnormal
This is a report of a 28-year-old female patient (weight: NA) from BE, suffering from the following health symptoms/conditions: thyroidectomy, who was treated with Levothyroxine(levothyroxine) (levothyroxine Sodium) (dosage: NA, start time: NS), combined with: NA. and developed a serious reaction and side effect(s): Caesarean Section, Nausea, Pre-eclampsia, Headache, Maternal Exposure During Pregnancy, Induced Labour, Foetal Heart Rate Abnormal after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Levothyroxine(levothyroxine) (levothyroxine Sodium) treatment in female patients, resulting in Caesarean Section side effect.
Levothyrox Side Effect Report#9970004
Blood Thyroid Stimulating Hormone Increased
This report suggests a potential Levothyrox (levothyroxine Sodium) (100 Microgram, Tablet) (levothyroxine Sodium) Blood Thyroid Stimulating Hormone Increased side effect(s) that can have serious consequences. A 65-year-old female patient (weight: NA) from FR was diagnosed with the following symptoms/conditions: NA and used Levothyrox (levothyroxine Sodium) (100 Microgram, Tablet) (levothyroxine Sodium) (dosage: NA) starting
Oct 21, 2013. After starting Levothyrox (levothyroxine Sodium) (100 Microgram, Tablet) (levothyroxine Sodium) the patient began experiencing various side effects, including: Blood Thyroid Stimulating Hormone IncreasedAdditional drugs used concurrently:
  • Victrelis ( Boceprevir) Capsule (2400 Mg (800 Mg, 3 In 1 D), Oral)
  • Viraferonpeg (peginterferon Alfa-2b) (injection) (peginterferon Alfa-2b) (120 Mcg, Cycle, Subcutaneous)
  • Rebetol (1 Gm (2-1-3) , Oral)
  • Exforge (amlodipne W/valsartan) (amlodipine, Valsartan)
  • Seroplex (escitalopram Oxalate) (escitalopram Oxalate)
Although Levothyrox (levothyroxine Sodium) (100 Microgram, Tablet) (levothyroxine Sodium) demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Blood Thyroid Stimulating Hormone Increased, may still occur.
Levothyrox Side Effect Report#9969655
Diverticulitis, Renal Failure, International Normalised Ratio Increased, Dyskinesia, Abdominal Pain, Leukocytosis, Muscle Twitching, Muscle Spasms, Grimacing
This Diverticulitis problem was reported by a pharmacist from US. A 77-year-old female patient (weight: NA) was diagnosed with the following symptoms/conditions: NA. On NS this consumer started treatment with Levothyroxine (dosage: NA). The following drugs were being taken at the same time:
  • Allopurinol (allopurinol)
  • Diltiazem Cd
  • Famotidine (famotidine)
  • Furosemide (furosemide)
  • Paroxetine (paroxetine)
  • Warfarin (warfarin)
  • Levofloxacin (levofloxacin)
  • Metronidazole (metronidazole) (500 Mg, 1 In 8 Hr, Intravenous)
When using Levothyroxine, the patient experienced the following unwanted symptoms/side effects: Diverticulitis, Renal Failure, International Normalised Ratio Increased, Dyskinesia, Abdominal Pain, Leukocytosis, Muscle Twitching, Muscle Spasms, GrimacingThe patient was hospitalized.Although all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Diverticulitis, may become evident only after a product is in use by the general population.
Levothyrox Side Effect Report#9958910
Product Substitution Issue, Blood Thyroid Stimulating Hormone Abnormal
This Product Substitution Issue side effect was reported by a consumer or non-health professional from US. A 61-year-old female patient (weight:NA) experienced the following symptoms/conditions: secondary hypothyroidism.The patient was prescribed Levothyroxine (drug dosage: NA), which was initiated on
Aug 27, 2012. Concurrently used drugs:
  • Fluocinolone (synalar)
.After starting to take Levothyroxine the consumer reported adverse symptoms, such as: Product Substitution Issue, Blood Thyroid Stimulating Hormone AbnormalThese side effects may potentially be related to Levothyroxine.
Levothyrox Side Effect Report#9951098
Insomnia, Anxiety, Feeling Jittery, Middle Insomnia, Myalgia, Muscular Weakness, Headache, Blood Thyroid Stimulating Hormone Increased, Abdominal Pain Upper
This is a report of a 71-year-old female patient (weight: NA) from US, suffering from the following health symptoms/conditions: thyroid disorder, who was treated with Levothyroxine Sodium (dosage: Unk, start time: NS), combined with: NA. and developed a serious reaction and side effect(s): Insomnia, Anxiety, Feeling Jittery, Middle Insomnia, Myalgia, Muscular Weakness, Headache, Blood Thyroid Stimulating Hormone Increased, Abdominal Pain Upper after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Levothyroxine Sodium treatment in female patients, resulting in Insomnia side effect.
Levothyrox Side Effect Report#9932908
Myocardial Infarction, Product Quality Issue, Chest Pain, Vomiting, Musculoskeletal Stiffness
This report suggests a potential Levothyrox Myocardial Infarction side effect(s) that can have serious consequences. A 62-year-old female patient (weight: NA) from FR was diagnosed with the following symptoms/conditions: NA and used Levothyrox (dosage: NA) starting NS. After starting Levothyrox the patient began experiencing various side effects, including: Myocardial Infarction, Product Quality Issue, Chest Pain, Vomiting, Musculoskeletal StiffnessAdditional drugs used concurrently:
  • Crestor (rosuvastain)
  • Stagid (metformin Embonate)
  • Fluoxetine (fluoxetine)
  • Coversyl
Although Levothyrox demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Myocardial Infarction, may still occur.
Levothyrox Side Effect Report#9925240
Renal Failure Acute
This Renal Failure Acute problem was reported by a physician from US. A 78-year-old female patient (weight: NA) was diagnosed with the following symptoms/conditions: NA. On
May 07, 2012 this consumer started treatment with Levothyroxine Sodium (dosage: NA). The following drugs were being taken at the same time:
  • Clopidogrel
  • Insulin Glargine
  • Insulin Glargine
  • Vitamin B6
  • Calcium
  • Isovue 370
  • Aspirin
When using Levothyroxine Sodium, the patient experienced the following unwanted symptoms/side effects: Renal Failure AcuteThe patient was hospitalized.Although all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Renal Failure Acute, may become evident only after a product is in use by the general population.
Levothyrox Side Effect Report#9924900
Accidental Exposure To Product
This Accidental Exposure To Product side effect was reported by a physician from Country Not Specified. A male patient (weight:NA) experienced the following symptoms/conditions: NA.The patient was prescribed Levothyroxine (drug dosage: NA), which was initiated on NS. Concurrently used drugs: NA..After starting to take Levothyroxine the consumer reported adverse symptoms, such as: Accidental Exposure To ProductThese side effects may potentially be related to Levothyroxine. The patient was hospitalized.
Levothyrox Side Effect Report#9924898
Accidental Exposure To Product
This is a report of a 15-year-old female patient (weight: NA) from Country Not Specified, suffering from the following health symptoms/conditions: NA, who was treated with Levothyroxine (dosage: 4.5-9.0 Mg Once, start time: NS), combined with: NA. and developed a serious reaction and side effect(s): Accidental Exposure To Product after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Levothyroxine treatment in female patients, resulting in Accidental Exposure To Product side effect. The patient was hospitalized.
Levothyrox Side Effect Report#9924877
Accidental Exposure To Product
This report suggests a potential Levothyroxine Accidental Exposure To Product side effect(s) that can have serious consequences. A male patient (weight: NA) from Country Not Specified was diagnosed with the following symptoms/conditions: NA and used Levothyroxine (dosage: NA) starting NS. After starting Levothyroxine the patient began experiencing various side effects, including: Accidental Exposure To ProductAdditional drugs used concurrently: NA.The patient was hospitalized. Although Levothyroxine demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Accidental Exposure To Product, may still occur.
Levothyrox Side Effect Report#9924874
Accidental Exposure To Product
This Accidental Exposure To Product problem was reported by a physician from Country Not Specified. A female patient (weight: NA) was diagnosed with the following symptoms/conditions: NA. On NS this consumer started treatment with Levothyroxine (dosage: 1.8-4.8 Mg Once). The following drugs were being taken at the same time: NA. When using Levothyroxine, the patient experienced the following unwanted symptoms/side effects: Accidental Exposure To ProductAlthough all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Accidental Exposure To Product, may become evident only after a product is in use by the general population.
Levothyrox Side Effect Report#9924872
Accidental Exposure To Product
This Accidental Exposure To Product side effect was reported by a physician from Country Not Specified. A 13-year-old female patient (weight:NA) experienced the following symptoms/conditions: NA.The patient was prescribed Levothyroxine (drug dosage: 4.5-9.0 Mg Once), which was initiated on NS. Concurrently used drugs: NA..After starting to take Levothyroxine the consumer reported adverse symptoms, such as: Accidental Exposure To ProductThese side effects may potentially be related to Levothyroxine. The patient was hospitalized.
Levothyrox Side Effect Report#9924871
Accidental Exposure To Product
This is a report of a 4-year-old male patient (weight: NA) from Country Not Specified, suffering from the following health symptoms/conditions: NA, who was treated with Levothyroxine (dosage: NA, start time: NS), combined with: NA. and developed a serious reaction and side effect(s): Accidental Exposure To Product after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Levothyroxine treatment in male patients, resulting in Accidental Exposure To Product side effect.
Levothyrox Side Effect Report#9924870
Accidental Exposure To Product
This report suggests a potential Levothyroxine Accidental Exposure To Product side effect(s) that can have serious consequences. A 4-year-old female patient (weight: NA) from Country Not Specified was diagnosed with the following symptoms/conditions: NA and used Levothyroxine (dosage: NA) starting NS. After starting Levothyroxine the patient began experiencing various side effects, including: Accidental Exposure To ProductAdditional drugs used concurrently: NA.The patient was hospitalized. Although Levothyroxine demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Accidental Exposure To Product, may still occur.
Levothyrox Side Effect Report#9924868
Accidental Exposure To Product
This Accidental Exposure To Product problem was reported by a physician from Country Not Specified. A male patient (weight: NA) was diagnosed with the following symptoms/conditions: NA. On NS this consumer started treatment with Levothyroxine (dosage: NA). The following drugs were being taken at the same time: NA. When using Levothyroxine, the patient experienced the following unwanted symptoms/side effects: Accidental Exposure To ProductThe patient was hospitalized.Although all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Accidental Exposure To Product, may become evident only after a product is in use by the general population.
Levothyrox Side Effect Report#9923993
Toxicity To Various Agents
This Toxicity To Various Agents side effect was reported by a physician from Country Not Specified. A 3-year-old male patient (weight:NA) experienced the following symptoms/conditions: NA.The patient was prescribed Levothyroxine (drug dosage: NA), which was initiated on NS. Concurrently used drugs: NA..After starting to take Levothyroxine the consumer reported adverse symptoms, such as: Toxicity To Various AgentsThese side effects may potentially be related to Levothyroxine.
Levothyrox Side Effect Report#9915874
Deep Vein Thrombosis, Dyspnoea, Palpitations, Oedema Peripheral, Hepatic Pain
This is a report of a 66-year-old female patient (weight: NA) from FR, suffering from the following health symptoms/conditions: NA, who was treated with Levothyrox (dosage: NA, start time: 201202), combined with:
  • Peginterferon Alfa-2a
  • Ribavirin
and developed a serious reaction and side effect(s): Deep Vein Thrombosis, Dyspnoea, Palpitations, Oedema Peripheral, Hepatic Pain after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Levothyrox treatment in female patients, resulting in Deep Vein Thrombosis side effect. The patient was hospitalized.


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The appearance of Levothyrox on this list does not mean that FDA has concluded that the drug has the listed risk. It means that FDA has identified a potential safety issue, but it does not mean that FDA has found a causal relationship between the drug and the listed risk.

What are common Levothyrox Side Effects for Women?

Women Side EffectsReports
Fatigue 192
Headache 160
Nausea 153
Dizziness 127
Alopecia 122
Pain 115
Asthenia 114
Dyspnoea 114
Product Substitution Issue 114
Malaise 110

What are common Levothyrox Side Effects for Men?

Men Side EffectsReports
Dyspnoea 37
Nausea 28
Fatigue 24
Asthenia 23
Diarrhoea 23
Pruritus 23
Pyrexia 21
Anaemia 20
Blood Thyroid Stimulating Hormone Increased 20
Headache 20

Track Your Side Effects

Note Your Observations

It is really important to keep track of your health symptoms, right from the time you start a new medicine. You can do it any way you prefer: in a notebook, in a computer file or using our online tool. You should also note down any other medicines you are taking at the same time, because there could be an interaction between these medicines.

Why Your Notes are Important

Your notes could be helpful in several ways:

  • You can use them to remind you of details that may alert your health care professional(s) to a problem
  • You will have a record to refer to in the future, in case you are ever prescribed the same medicine again

  • Log Form

    You can use the following log form to write down important information, like the date and time you experienced a side effect and your symptoms, how strong the symptoms were, and any other medicines you were using.

    Medicine Name and Dosage:
    Side Effects Scale Date & Time Other Medicine(s) or Treatment(s)
    Scale: 1 = very mild to 10 = very bad

    Side effects reports are analyzed to discover potential health product safety signals. Some important reactions may take an extremely long time to develop or occur infrequently. Continued monitoring of adverse reactions is thus essential to maintain a comprehensive safety and effectiveness profile of health products.

    You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

    Levothyrox reports list potential signals of serious risks and new safety information that were identified using the FDA Adverse Event Reporting System (FAERS).
    FAERS is a database that contains information on adverse event and medication errors reports submitted to FDA by healthcare professionals (such as physicians, pharmacists, nurses and others), consumers (such as patients, family members, layers and others) and manufacturers.

    Discuss Levothyrox Side Effects

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    How Effective is Levothyrox for You?

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    Levothyrox Safety Alerts, Active Ingredients, Usage Information

    NDC0378-1800
    TypeHUMAN PRESCRIPTION DRUG
    Proprietary NameLevothyroxine Sodium
    Namelevothyroxine sodium
    Dosage FormTABLET
    RouteORAL
    On market since20021101
    LabelerMylan Pharmaceuticals Inc.
    Active Ingredient(s)LEVOTHYROXINE SODIUM
    Strength(s)25
    Unit(s)ug/1
    Pharma Classl-Thyroxine [EPC],Thyroxine [Chemical/Ingredient]

    More About Levothyrox

    Side Effects reported to FDA: 3801

    Levothyrox safety alerts: 2004

    Reported deaths: 215

    Reported hospitalizations: 1145

    Levoxyl (levothyroxine sodium)

    Audience: Endocrinologists and other healthcare professionals

    FDA and King Pharmaceuticals notified healthcare professionals of revisions to the PRECAUTIONS, ADVERSE REACTIONS and DOSAGE AND ADMINISTRATION sections of labeling, describing reports of choking, gagging, tablets stuck in throat and dysphagia while taking Levoxyl. These reports have predominately occurred when Levoxyl tablets were not taken with water. It is recommended that Levoxyl tablets be taken with a full glass of water.

    [September 17, 2004 - Letter - King Pharmaceuticals]

    Latest Levothyrox clinical trials