What the label lists and what reports show
Macitentan side effects
Macitentan's FDA label: “Most common adverse reactions (more frequent than placebo by ≥3%) are anemia, nasopharyngitis/pharyngitis, bronchitis, headache, influenza, and urinary tract infection ( 6.1 ).” FAERS holds 68,840 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 (11,956 reports).
- Generic listed
- Boxed warning
Check it at the source: the macitentan FDA label on DailyMed (effective April 11, 2025, Actelion Pharmaceuticals US, Inc.); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of OPSUMIT?OPSUMIT can cause serious side effects, including: Serious birth defects. See " What is the most important information I should know about OPSUMIT? " Some medicines that are like OPSUMIT can cause liver problems. Your healthcare provider should do blood tests to check your liver before you start taking OPSUMIT. Tell your healthcare provider if you have any of the following symptoms of liver problems while taking OPSUMIT. nausea or vomiting pain in the upper right stomach tiredness loss of appetite yellowing of your skin or whites of your eyes dark urine fever itching Fluid retention can happen within weeks after starting OPSUMIT. Tell your healthcare provider right away if you have any unusual weight gain or swelling of your ankles or legs. Your healthcare provider will look for the cause of any fluid retention. […]
Source: FDA drug label, Actelion Pharmaceuticals US, Inc., effective April 11, 2025 (SPL set 1e484a50-55db-4b85-8c57-6cd1b0353abd), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (more frequent than placebo by ≥3%) are anemia, nasopharyngitis/pharyngitis, bronchitis, headache, influenza, and urinary tract infection ( 6.1 ).
Table 2: Adverse Reactions
| Adverse Reaction | OPSUMIT 10 mg (N=242) (%) | Placebo (N=249) (%) |
|---|---|---|
| Anemia | 13 | 3 |
| Nasopharyngitis/pharyngitis | 20 | 13 |
| Bronchitis | 12 | 6 |
| Headache | 14 | 9 |
| Influenza | 6 | 2 |
| Urinary tract infection | 9 | 6 |
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, continuedClinically significant adverse reactions that appear in other sections of the labeling include: Embryo-fetal Toxicity [see Warnings and Precautions (5.1) ] Hepatotoxicity [see Warnings and Precautions (5.2) ] Fluid Retention [see Warnings and Precautions (5.3) ] Decrease in Hemoglobin [see Warnings and Precautions (5.4) ] Most common adverse reactions (more frequent than placebo by ≥3%) are anemia, nasopharyngitis/pharyngitis, bronchitis, headache, influenza, and urinary tract infection ( 6.1 ). To report SUSPECTED ADVERSE REACTIONS, contact Actelion at 1-800-526-7736 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trial Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in 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 clinical practice. Safety data for OPSUMIT were obtained primarily from one placebo-controlled clinical study in 742 patients with PAH (SERAPHIN study) [see Clinical Studies (14.1) ]. The exposure to OPSUMIT in this trial was up to 3.6 years with a median exposure of about 2 years (N=542 for 1 year; N=429 for 2 years; and N=98 for more than 3 years). …
Source: FDA drug label, Actelion Pharmaceuticals US, Inc., effective April 11, 2025 (SPL set 1e484a50-55db-4b85-8c57-6cd1b0353abd), via openFDA; the full label on DailyMed
What do FAERS reports show?
68,840 reports list macitentan among the medicines taken, each a report of something that happened, not proof the medicine caused it; 12,527 are coded as a death and 34,017 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 21 reactions below, 6 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?
- Macitentan: 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