Common Synthroid Side Effects


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

Fatigue (466)
Alopecia (297)
Headache (269)
Dizziness (265)
Nausea (255)
Weight Increased (238)
Feeling Abnormal (212)
Insomnia (209)
Palpitations (208)
Anxiety (200)
Blood Thyroid Stimulating Hormone Increased (198)
Diarrhoea (192)
Dyspnoea (187)
Rash (178)
Pain (172)
Pruritus (170)
Asthenia (164)
Arthralgia (160)
Malaise (140)
Chest Pain (130)

➢ 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.

Synthroid Side Effects Reported to FDA



Synthroid Side Effect Report#9994756
Alopecia, Dyspnoea, Memory Impairment, Bone Loss, Hypotonia, Product Substitution Issue
This is a report of a 18-year-old female patient (weight: NA) from US, suffering from the following health symptoms/conditions: thyroid disorder, who was treated with Synthroid (dosage: 175 Mg 1 Pill Daily 4days A Week, start time: 2003), combined with:
  • Vitamin D
and developed a serious reaction and side effect(s): Alopecia, Dyspnoea, Memory Impairment, Bone Loss, Hypotonia, Product Substitution Issue after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Synthroid treatment in female patients, resulting in Alopecia side effect.
Synthroid Side Effect Report#9987988
Uterine Leiomyoma, Product Substitution Issue, Haemoglobin Decreased, Rash, Urticaria, Dermatitis Contact, Flushing, Pain Of Skin, House Dust Allergy
This report suggests a potential Synthroid Uterine Leiomyoma side effect(s) that can have serious consequences. A 61-year-old female patient (weight: NA) from US was diagnosed with the following symptoms/conditions: hypothyroidism and used Synthroid (dosage: NA) starting NS. After starting Synthroid the patient began experiencing various side effects, including: Uterine Leiomyoma, Product Substitution Issue, Haemoglobin Decreased, Rash, Urticaria, Dermatitis Contact, Flushing, Pain Of Skin, House Dust AllergyAdditional drugs used concurrently: NA. Although Synthroid demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Uterine Leiomyoma, may still occur.
Synthroid Side Effect Report#9974997
Asthenia, Skin Lesion
This Asthenia problem was reported by a consumer or non-health professional from US. A 77-year-old female patient (weight: NA) was diagnosed with the following symptoms/conditions: hypothyroidism. On 201309 this consumer started treatment with Synthroid (dosage: NA). The following drugs were being taken at the same time:
  • Mercaptopurine
  • Humira
  • Humira (2 Weeks After The Initial Dose)
  • Humira (4 Weeks After The Initial Dose)
  • Tylenol
  • Alprazolam (As Needed)
  • Atorvastatin
  • Prednisone
When using Synthroid, the patient experienced the following unwanted symptoms/side effects: Asthenia, Skin LesionAlthough all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Asthenia, may become evident only after a product is in use by the general population.
Synthroid Side Effect Report#9963955
Renal Failure, Coeliac Disease
This Renal Failure side effect was reported by a health professional from US. A female patient (weight:NA) experienced the following symptoms/conditions: hypothyroidism,hypertension,diabetes mellitus.The patient was prescribed Synthroid (drug dosage: NA), which was initiated on 1992. Concurrently used drugs:
  • Clonidine
  • Glimepiride
  • Januvia
  • Nifedipine
  • Diovan
.After starting to take Synthroid the consumer reported adverse symptoms, such as: Renal Failure, Coeliac DiseaseThese side effects may potentially be related to Synthroid.
Synthroid Side Effect Report#9948722
Thyroid Cancer, Haemorrhage, Blood Thyroid Stimulating Hormone Abnormal
This is a report of a female patient (weight: NA) from US, suffering from the following health symptoms/conditions: hypothyroidism, who was treated with Synthroid (dosage: NA, start time: 1992), combined with:
  • Multivitamin
  • Calcium
  • Iron
  • Zinc
and developed a serious reaction and side effect(s): Thyroid Cancer, Haemorrhage, Blood Thyroid Stimulating Hormone Abnormal after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Synthroid treatment in female patients, resulting in Thyroid Cancer side effect.
Synthroid Side Effect Report#9933102
Juvenile Myoclonic Epilepsy
This report suggests a potential Synthroid Juvenile Myoclonic Epilepsy side effect(s) that can have serious consequences. A 19-year-old male patient (weight: NA) from US was diagnosed with the following symptoms/conditions: hypothyroidism,growth hormone deficiency and used Synthroid (dosage: NA) starting
Jul 13, 2010. After starting Synthroid the patient began experiencing various side effects, including: Juvenile Myoclonic EpilepsyAdditional drugs used concurrently:
  • Saizen
  • Cortef (250, Tab, If Ill)
  • Doryx
  • Nitropen
Although Synthroid demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Juvenile Myoclonic Epilepsy, may still occur.
Synthroid Side Effect Report#9929270
Body Temperature Decreased, Hypothyroidism, Fatigue, Constipation, Weight Increased
This Body Temperature Decreased problem was reported by a consumer or non-health professional from US. A 51-year-old female patient (weight: NA) was diagnosed with the following symptoms/conditions: autoimmune thyroiditis. On 2013 this consumer started treatment with Synthroid (dosage: One And A Half Tablets To Equal 75mcg/day.). The following drugs were being taken at the same time: NA. When using Synthroid, the patient experienced the following unwanted symptoms/side effects: Body Temperature Decreased, Hypothyroidism, Fatigue, Constipation, Weight IncreasedAlthough all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Body Temperature Decreased, may become evident only after a product is in use by the general population.
Synthroid Side Effect Report#9915270
Coeliac Disease, Failure To Thrive
This Coeliac Disease side effect was reported by a consumer or non-health professional from US. A 13-year-old female patient (weight:NA) experienced the following symptoms/conditions: hypothyroidism.The patient was prescribed Synthroid (drug dosage: NA), which was initiated on 2000. Concurrently used drugs:
  • Vitamin D
.After starting to take Synthroid the consumer reported adverse symptoms, such as: Coeliac Disease, Failure To ThriveThese side effects may potentially be related to Synthroid.
Synthroid Side Effect Report#9914603
Cerebrospinal Fluid Leakage, Cerebrospinal Fluid Leakage, Dural Tear, Cerebrospinal Fluid Leakage, Csf Pressure Increased, Skull Fractured Base, Headache, Balance Disorder, Benign Intracranial Hypertension
This is a report of a female patient (weight: NA) from US, suffering from the following health symptoms/conditions: hypothyroidism,hypertension,gastrooesophageal reflux disease,respiratory tract congestion,depression, who was treated with Synthroid (dosage: NA, start time: 1990), combined with:
  • Cozaar
  • Protonix
  • Singulair
  • Wellbutrin
  • Effexor
  • Multivitamin
  • Aspirin
and developed a serious reaction and side effect(s): Cerebrospinal Fluid Leakage, Cerebrospinal Fluid Leakage, Dural Tear, Cerebrospinal Fluid Leakage, Csf Pressure Increased, Skull Fractured Base, Headache, Balance Disorder, Benign Intracranial Hypertension after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Synthroid treatment in female patients, resulting in Cerebrospinal Fluid Leakage side effect.
Synthroid Side Effect Report#9898033
Blood Thyroid Stimulating Hormone Increased
This report suggests a potential Synthroid Blood Thyroid Stimulating Hormone Increased side effect(s) that can have serious consequences. A male patient (weight: NA) from US was diagnosed with the following symptoms/conditions: hypothyroidism and used Synthroid (dosage: NA) starting NS. After starting Synthroid the patient began experiencing various side effects, including: Blood Thyroid Stimulating Hormone IncreasedAdditional drugs used concurrently: NA.The patient was hospitalized. Although Synthroid demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Blood Thyroid Stimulating Hormone Increased, may still occur.
Synthroid Side Effect Report#9897634
Thyroid Cancer Metastatic, Rash
This Thyroid Cancer Metastatic problem was reported by a consumer or non-health professional from US. A female patient (weight: NA) was diagnosed with the following symptoms/conditions: hypothyroidism,ulcer. On 1959 this consumer started treatment with Synthroid (dosage: NA). The following drugs were being taken at the same time:
  • Protonix
  • Evista
When using Synthroid, the patient experienced the following unwanted symptoms/side effects: Thyroid Cancer Metastatic, RashAlthough all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Thyroid Cancer Metastatic, may become evident only after a product is in use by the general population.
Synthroid Side Effect Report#9890443
Palpitations, Oedema, Alopecia, Product Substitution Issue
This Palpitations side effect was reported by a physician from US. A 34-year-old female patient (weight:NA) experienced the following symptoms/conditions: hypothyroidism.The patient was prescribed Synthroid 125 Mcg (drug dosage: Lifetime), which was initiated on NS. Concurrently used drugs: NA..After starting to take Synthroid 125 Mcg the consumer reported adverse symptoms, such as: Palpitations, Oedema, Alopecia, Product Substitution IssueThese side effects may potentially be related to Synthroid 125 Mcg.
Synthroid Side Effect Report#9887482
Chest Pain, Loss Of Consciousness, Dizziness, Aortic Aneurysm, Intervertebral Disc Protrusion, Osteoarthritis, Osteoporosis
This is a report of a 56-year-old female patient (weight: NA) from US, suffering from the following health symptoms/conditions: hypothyroidism, who was treated with Synthroid (dosage: NA, start time: 1990), combined with: NA. and developed a serious reaction and side effect(s): Chest Pain, Loss Of Consciousness, Dizziness, Aortic Aneurysm, Intervertebral Disc Protrusion, Osteoarthritis, Osteoporosis after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Synthroid treatment in female patients, resulting in Chest Pain side effect.
Synthroid Side Effect Report#9883331
Constipation
This report suggests a potential Synthroid Constipation side effect(s) that can have serious consequences. A 80-year-old male patient (weight: NA) from US was diagnosed with the following symptoms/conditions: hypothyroidism and used Synthroid (dosage: NA) starting 201312. After starting Synthroid the patient began experiencing various side effects, including: ConstipationAdditional drugs used concurrently:
  • Levothyroxine
  • Clonazepam
  • Irbesartan
  • Finasteride
  • Pantoprazole
  • Black Cherry
  • Proair
  • Fish Oil
The patient was hospitalized. Although Synthroid demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Constipation, may still occur.
Synthroid Side Effect Report#9879786
Chest Pain, Malaise, Urticaria, Scar, Weight Increased, Autoimmune Thyroiditis
This Chest Pain problem was reported by a consumer or non-health professional from US. A female patient (weight: NA) was diagnosed with the following symptoms/conditions: NA. On NS this consumer started treatment with Synthroid (dosage: NA). The following drugs were being taken at the same time:
  • Cytomel
  • Armour Thyroid
  • Tirosint
When using Synthroid, the patient experienced the following unwanted symptoms/side effects: Chest Pain, Malaise, Urticaria, Scar, Weight Increased, Autoimmune ThyroiditisThe 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 Chest Pain, may become evident only after a product is in use by the general population.
Synthroid Side Effect Report#9868251
Blood Thyroid Stimulating Hormone Increased, Blood Pressure Systolic Increased, Fatigue, Somnolence, Thyroxine Decreased, Tri-iodothyronine Increased
This Blood Thyroid Stimulating Hormone Increased side effect was reported by a physician from CA. A 61-year-old male patient (weight:NA) experienced the following symptoms/conditions: NA.The patient was prescribed Synthroid (drug dosage: NA), which was initiated on NS. Concurrently used drugs:
  • Thyroid
.After starting to take Synthroid the consumer reported adverse symptoms, such as: Blood Thyroid Stimulating Hormone Increased, Blood Pressure Systolic Increased, Fatigue, Somnolence, Thyroxine Decreased, Tri-iodothyronine IncreasedThese side effects may potentially be related to Synthroid.
Synthroid Side Effect Report#9864016
Fall, Laceration, Contusion, Clavicle Fracture, Madarosis, Alopecia, Unevaluable Event, Blood Calcium Decreased, Tooth Disorder
This is a report of a 77-year-old female patient (weight: NA) from Country Not Specified, suffering from the following health symptoms/conditions: hypothyroidism, who was treated with Synthroid (dosage: NA, start time: NS), combined with: NA. and developed a serious reaction and side effect(s): Fall, Laceration, Contusion, Clavicle Fracture, Madarosis, Alopecia, Unevaluable Event, Blood Calcium Decreased, Tooth Disorder after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Synthroid treatment in female patients, resulting in Fall side effect.
Synthroid Side Effect Report#9857030
Visual Impairment, Insomnia, Hypoaesthesia Oral, Headache, Palpitations
This report suggests a potential Synthroid Visual Impairment side effect(s) that can have serious consequences. A female patient (weight: NA) from US was diagnosed with the following symptoms/conditions: thyroidectomy and used Synthroid (dosage: NA) starting NS. After starting Synthroid the patient began experiencing various side effects, including: Visual Impairment, Insomnia, Hypoaesthesia Oral, Headache, PalpitationsAdditional drugs used concurrently: NA. Although Synthroid demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Visual Impairment, may still occur.
Synthroid Side Effect Report#9856943
Pancreatic Carcinoma, Unevaluable Event, Feeling Abnormal, Hypoaesthesia Oral
This Pancreatic Carcinoma problem was reported by a consumer or non-health professional from US. A female patient (weight: NA) was diagnosed with the following symptoms/conditions: hypothyroidism. On NS this consumer started treatment with Synthroid (dosage: NA). The following drugs were being taken at the same time: NA. When using Synthroid, the patient experienced the following unwanted symptoms/side effects: Pancreatic Carcinoma, Unevaluable Event, Feeling Abnormal, Hypoaesthesia OralAlthough all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Pancreatic Carcinoma, may become evident only after a product is in use by the general population.
Synthroid Side Effect Report#9851196
Abortion Incomplete, Urinary Tract Infection
This Foetal Death side effect was reported by a consumer or non-health professional from BR. A 32-year-old female patient (weight:NA) experienced the following symptoms/conditions: hypothyroidism.The patient was prescribed Synthroid (drug dosage: NA), which was initiated on 201310. Concurrently used drugs: NA..After starting to take Synthroid the consumer reported adverse symptoms, such as: Abortion Incomplete, Urinary Tract InfectionThese side effects may potentially be related to Synthroid.
Synthroid Side Effect Report#9850918
Pneumonia
This is a report of a 92-year-old female patient (weight: NA) from US, suffering from the following health symptoms/conditions: NA, who was treated with Synthroid (dosage: NA, start time: NS), combined with: NA. and developed a serious reaction and side effect(s): Pneumonia after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Synthroid treatment in female patients, resulting in Pneumonia side effect.
Synthroid Side Effect Report#9840387
Abnormal Behaviour, Fatigue, Confusional State
This report suggests a potential Synthroid Abnormal Behaviour 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 Synthroid (dosage: NA) starting 1997. After starting Synthroid the patient began experiencing various side effects, including: Abnormal Behaviour, Fatigue, Confusional StateAdditional drugs used concurrently: NA. Although Synthroid demonstrated significant improvements in a number of clinically relevant cases, troublesome symptoms, such as Abnormal Behaviour, may still occur.
Synthroid Side Effect Report#9835887
Unevaluable Event
This Unevaluable Event 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,diabetes mellitus. On NS this consumer started treatment with Synthroid (dosage: Varying Doses). The following drugs were being taken at the same time:
  • Insulin
When using Synthroid, the patient experienced the following unwanted symptoms/side effects: Unevaluable EventAlthough all drugs are carefully tested before they are licensed for use, they carry side effect risks. Some side effects, such as Unevaluable Event, may become evident only after a product is in use by the general population.
Synthroid Side Effect Report#9823293
Uterine Cancer, Urticaria, Urticaria, Urinary Tract Infection, Pruritus
This Uterine Cancer side effect was reported by a physician from US. A female patient (weight:NA) experienced the following symptoms/conditions: NA.The patient was prescribed Synthroid (drug dosage: NA), which was initiated on 201310. Concurrently used drugs:
  • Cipro
  • Protosel-otc Supplement
.After starting to take Synthroid the consumer reported adverse symptoms, such as: Uterine Cancer, Urticaria, Urticaria, Urinary Tract Infection, PruritusThese side effects may potentially be related to Synthroid.
Synthroid Side Effect Report#9817149
Weight Decreased, Vomiting, Intestinal Ischaemia, Abdominal Pain, Hypophagia, Malabsorption, Blood Thyroid Stimulating Hormone Increased
This is a report of a 78-year-old female patient (weight: NA) from US, suffering from the following health symptoms/conditions: thyroidectomy,hypertension, who was treated with Synthroid (dosage: NA, start time: 1999), combined with: NA. and developed a serious reaction and side effect(s): Weight Decreased, Vomiting, Intestinal Ischaemia, Abdominal Pain, Hypophagia, Malabsorption, Blood Thyroid Stimulating Hormone Increased after the beginning of treatment. This case can indicate the possible existence of increased vulnerability to Synthroid treatment in female patients, resulting in Weight Decreased side effect. The patient was hospitalized.


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The appearance of Synthroid 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 Synthroid Side Effects for Women?

Women Side Effects Reports
Fatigue 404
Alopecia 284
Headache 241
Dizziness 233
Nausea 225
Weight Increased 224
Feeling Abnormal 195
Palpitations 187
Insomnia 181
Anxiety 172

What are common Synthroid Side Effects for Men?

Men Side Effects Reports
Fatigue 58
Blood Thyroid Stimulating Hormone Increased 41
Anxiety 28
Asthenia 28
Dizziness 28
Nausea 27
Headache 26
Insomnia 26
Dyspnoea 24
Rash 24

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.

    Synthroid 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.

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    Synthroid Safety Alerts, Active Ingredients, Usage Information

    NDC 0074-3727
    Type HUMAN PRESCRIPTION DRUG
    Proprietary Name Synthroid
    Name Levothyroxine Sodium
    Dosage Form TABLET
    Route ORAL
    On market since 20020724
    Labeler AbbVie Inc.
    Active Ingredient(s) LEVOTHYROXINE SODIUM
    Strength(s) 137
    Unit(s) ug/1
    Pharma Class l-Thyroxine [EPC],Thyroxine [Chemical/Ingredient]

    Synthroid Dosage, Warnings, Usage.

    Side Effects reported to FDA: 4452

    Synthroid safety alerts: No

    Reported deaths: 202

    Reported hospitalizations: 991

    Latest Synthroid clinical trials