What the label lists and what reports show
Acetylcysteine side effects
Acetylcysteine's FDA label: “Most common adverse reactions (> 2%) are rash, urticaria/facial flushing and pruritus ( 6.1 ).” FAERS holds 9,369 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is dyspnoea (780 reports).
- Generic listed
Check it at the source: the acetylcysteine FDA label on DailyMed (effective May 6, 2026, Glenmark Pharmaceuticals Inc., USA); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsMost common adverse reactions (> 2%) are rash, urticaria/facial flushing and pruritus ( 6.1 ).
A table the label prints in its adverse reactions section without a title; its column headings name the groups compared
| Treatment Group Number of Patients | 15-minutes n=109 | 60-minutes n=71 |
|---|---|---|
| Cardiac disorders | 5 (5%) | 2 (3%) |
| Gastrointestinal disorders | 16 (15%) | 7 (10%) |
| Immune System Disorders | 20 (18%) | 10 (14%) |
| Respiratory, thoracic and mediastinal disorders | 2 (2%) | 2 (3%) |
| Skin & subcutaneous tissue disorders | 6 (6%) | 5 (7%) |
| Vascular disorders | 2 (2%) | 3 (4%) |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedMost common adverse reactions (> 2%) are rash, urticaria/facial flushing and pruritus ( 6.1 ). To report SUSPECTED ADVERSE REACTIONS, contact Glenmark Pharmaceuticals Inc., USA at 1 (888) 721-7115 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Studies Experience The following clinically significant adverse reactions are described elsewhere in labeling: • Hypersensitivity Reactions [see Warnings and Precautions ( 5.1 )] • Fluid Overload [see Warnings and Precautions ( 5.2 )] Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. In the literature the most frequently reported adverse reactions attributed to intravenous acetylcysteine administration were rash, urticaria and pruritus. The frequency of adverse reactions has been reported to be between 0.2% and 21%, and they most commonly occur during the initial loading dose of acetylcysteine. Loading Dose/Infusion Rate Study In a randomized, open-label, multi-center clinical study conducted in Australia in patients with acetaminophen poisoning, the rates of hypersensitivity reactions between a 15-minute and 60-minute intravenous infusion for the 150 mg/kg loading dose of acetylcysteine were compared. …
Source: FDA drug label, Glenmark Pharmaceuticals Inc., USA, effective May 6, 2026 (SPL set f811ddfc-d7c1-4637-ae81-80c38a77cb80), via openFDA; the full label on DailyMed
What do FAERS reports show?
9,369 reports list acetylcysteine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,754 are coded as a death and 5,080 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 20 reactions below, 5 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Acetylcysteine: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions