Synthroid: adverse event reports filed with FDA

26,831

reports as suspect product

0.1% of all reports · about 1,193 a year

1,910

reports, 12 months to June 2026

1,140 in the 12 months before

38.1%

marked serious by the reporter

48.4% across the class

6.8%

record death among outcomes, as reported

1,831 reports · not verified by FDA

Reports by month, five years

Reports by the month FDA received them. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.

By year received

2026 covers reports received through June 2026 only.

Reactions recorded in the reports

share of Synthroid reports recording the termmedian drug in l-thyroxine

1. Fatiguetiredness10.2%2,724
2. Drug ineffectivethe medicine did not work as expected9.7%2,595
3. Alopeciahair loss7%1,875
4. Weight increasedweight gain5.8%1,558
5. Feeling abnormalfeeling odd or not right5.3%1,427
6. Headachehead pain5.2%1,396
7. Malaisegeneral feeling of being unwell4.9%1,308
8. Palpitationsawareness of the heartbeat4.6%1,232
9. Nauseafeeling sick4.2%1,135
10. Astheniaweakness or lack of energy4%1,074
11. Painpain, site not specified3.9%1,057
12. Blood thyroid stimulating hormone increased3.9%1,048
13. Dyspnoeashortness of breath3.7%989
14. Anxietyanxiety3.5%947
15. Dizzinesslight-headedness or unsteadiness3.5%932
16. Insomniadifficulty sleeping3.4%919
17. Deaththe patient died; cause not stated by this term3.2%857
18. Weight decreasedweight loss3.1%825
19. Rashskin rash2.9%777
20. Diarrhoealoose or frequent stools2.9%766
21. Hypothyroidismunderactive thyroid2.8%764
22. Adverse drug reactiona harmful or unpleasant reaction reported to a medicine2.8%749
23. Hypertensionhigh blood pressure2.4%657
24. Asthmaasthma2.4%634
25. Falla fall2.4%633
26. Pruritusitching2.3%629
27. Coughcough2.3%624
28. Drug hypersensitivityan allergic-type reaction to a medicine2.3%617
29. Arthralgiajoint pain2.3%607
30. Pneumonialung infection2.1%571

Top 30 of 1,798 MedDRA preferred terms recorded across these reports, with a plain-language gloss where one is available. One report can record several terms. The hollow bar is the median share across the 6 drugs in the l-thyroxine class; it describes the reports, not the patients. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Outcomes recorded

Outcome flags as the reporter set them; a report can carry several, and "other serious" is FDA's own category for serious reports outside the named outcomes. Grey bar: all 51,210 reports in the class. FDA has not verified any outcome and states that the reports "cannot be used to estimate the incidence of these events."

Patients and reporters

Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 89.1% of reports give the United States as the country of the event or reporter.

Reason for use recorded

The indication field is filled in by the reporter and is often blank; shares are of all 26,831 reports.

Drugs most often listed in the same reports

Other products listed in reports where Synthroid is a suspect product, whatever their own role. Co-listing means the two were recorded together; it says nothing about either product's part in the event. Only the 2,500 most-reported names are counted here.

In context

Shares are of reports, not of patients treated. The number of people taking a product is not in the data, so none of these figures is a rate, and differences between columns reflect who takes a product, who reports and how long it has been sold. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Other drugs in the l-thyroxine class

Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." A brand and its generic are separate rows because reporters name them separately.

Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A report counts here when it lists Synthroid as a suspect or interacting product; reports listing it only as a concomitant medication (156,961) are excluded. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.