Drug class · FAERS comparison
Opioid Agonist side effects compared: 4 drugs, 310,401 FDA adverse event reports
How to read this page. Report counts are not incidence rates: a drug with more reports is usually older, more widely used or more publicised, not more dangerous.
Signals are screened against each product's FDA label on its own page; a term flagged across most of a class usually reflects the shared mechanism or the shared patient population.
Members
| Drug | FAERS reports | Serious | Death outcome | Boxed warning | Top labeled signals | Unlabeled (unassessed) |
|---|---|---|---|---|---|---|
| Morphine (Opium) | 120,577 | 86% | 34,831 | – | – | – |
| Fentanyl (Fentanyl System) | 97,898 | 85% | 27,747 | boxed | Serotonin syndrome; Respiratory depression; Prescription drug used without a prescription | Anaesthetic complication neurological; Delayed recovery from anaesthesia |
| Morphine (Opium) | 74,159 | 87% | 20,345 | – | – | – |
| Fentanyl (Fentanyl System) | 17,767 | 88% | 6,170 | boxed | Dependence; Respiratory arrest; Drug withdrawal syndrome neonatal | Ill-defined disorder; Developmental delay |
Class-wide signals (flagged in at least 2 of 4 members)
| Reaction | Members flagged | Median PRR | Reports (sum) | In label |
|---|---|---|---|---|
| Vaginal flatulence | 4/4 | 150.0 | 423 | 0/4 members' labels |
| Female genital tract fistula | 4/4 | 19.7 | 501 | 0/4 members' labels |
| Radiculopathy | 4/4 | 14.8 | 571 | 0/4 members' labels |
| Respiratory depression | 3/4 | 20.5 | 1,983 | 2/3 members' labels |
| Neuromuscular block prolonged | 2/4 | 76.8 | 129 | 0/2 members' labels |
| Substance dependence | 2/4 | 62.1 | 160 | 1/2 members' labels |
| Dependence | 2/4 | 53.6 | 8,938 | 1/2 members' labels |
| Neurologic neglect syndrome | 2/4 | 53.4 | 213 | 0/2 members' labels |
| Lupus vulgaris | 2/4 | 51.0 | 438 | 0/2 members' labels |
| Delayed recovery from anaesthesia | 2/4 | 49.2 | 235 | 0/2 members' labels |
| Amnestic disorder | 2/4 | 48.1 | 106 | 0/2 members' labels |
| Learning disorder | 2/4 | 42.9 | 328 | 0/2 members' labels |
| Retinitis | 2/4 | 37.6 | 496 | 0/2 members' labels |
| Procedural hypotension | 2/4 | 36.9 | 149 | 0/2 members' labels |
| Hyperthermia malignant | 2/4 | 35.2 | 264 | 2/2 members' labels |
| Carotid artery thrombosis | 2/4 | 32.5 | 214 | 0/2 members' labels |
| Seronegative arthritis | 2/4 | 31.5 | 271 | 0/2 members' labels |
| Drug withdrawal syndrome neonatal | 2/4 | 31.1 | 2,922 | 1/2 members' labels |
| Hypermobility syndrome | 2/4 | 26.9 | 70 | 0/2 members' labels |
| Accidental death | 2/4 | 22.2 | 304 | 1/2 members' labels |
| Developmental delay | 2/4 | 22.0 | 1,287 | 0/2 members' labels |
| Adjustment disorder | 2/4 | 20.6 | 215 | 0/2 members' labels |
| Bone erosion | 2/4 | 18.5 | 541 | 0/2 members' labels |
| Temperature regulation disorder | 2/4 | 17.4 | 340 | 0/2 members' labels |
| Substance use disorder | 2/4 | 14.5 | 391 | 0/2 members' labels |
Member-specific signals (flagged in exactly one drug)
| Reaction | Drug | Reports | PRR | Label screen |
|---|---|---|---|---|
| Grip strength | Morphine | 102 | 223.3 | No label text to screen |
| Presbyacusis | Fentanyl | 144 | 185.8 | Not in label — unassessed |
| Inspiratory capacity decreased | Fentanyl | 99 | 120.4 | Not in label — unassessed |
| Anaesthetic complication neurological | Fentanyl | 309 | 110.0 | Not in label — unassessed |
| Victim of homicide | Fentanyl | 134 | 66.5 | Not in label — unassessed |
| Speech disorder developmental | Fentanyl | 138 | 59.3 | Not in label — unassessed |
| Learning disability | Morphine | 1,171 | 48.1 | No label text to screen |
| Pleural thickening | Fentanyl | 112 | 42.0 | Not in label — unassessed |
| Adjustment disorder with depressed mood | Morphine | 253 | 40.5 | No label text to screen |
| Pleural fibrosis | Fentanyl | 164 | 40.4 | Not in label — unassessed |
| Intensive care unit acquired weakness | Fentanyl | 60 | 39.8 | Labeled (related wording) |
| Vision abnormal neonatal | Morphine | 79 | 39.8 | No label text to screen |
| Dislocation of vertebra | Morphine | 273 | 39.5 | No label text to screen |
| Deep vein thrombosis postoperative | Morphine | 208 | 33.5 | No label text to screen |
| Multiple drug overdose accidental | Morphine | 74 | 32.9 | No label text to screen |
| Propofol infusion syndrome | Fentanyl | 94 | 32.8 | Not in label — unassessed |
| Respiratory arrest | Fentanyl | 737 | 32.1 | Labeled adverse reaction |
| Proctitis | Fentanyl | 74 | 32.0 | Not in label — unassessed |
| Drug withdrawal syndrome | Morphine | 13,752 | 31.8 | No label text to screen |
| Emotional distress | Morphine | 16,962 | 28.1 | No label text to screen |
| Porphyria acute | Morphine | 123 | 27.6 | No label text to screen |
| Attention deficit hyperactivity disorder | Fentanyl | 92 | 26.7 | Not in label — unassessed |
| Bradycardia foetal | Fentanyl | 89 | 26.0 | Not in label — unassessed |
| Ill-defined disorder | Fentanyl | 1,288 | 25.5 | Not in label — unassessed |
| Bronchopulmonary aspergillosis allergic | Morphine | 115 | 24.8 | No label text to screen |
Common questions
Which opioid agonist has the most FDA adverse event reports?
Morphine has the most FAERS co-reports in this class (120,577), followed by Fentanyl (97,898). Report volume tracks how widely and how long a drug has been used, and how much attention it has had, far more than its risk.
Which side effects are shared across opioid agonist drugs?
Reaction terms flagged in at least half of the 4 members include vaginal flatulence, female genital tract fistula, radiculopathy, respiratory depression, neuromuscular block prolonged. A term shared across a class usually reflects the shared mechanism (or the shared patient population) rather than one product.
Does a FAERS signal mean the drug causes the reaction?
No. These are disproportionality signals from voluntary reports with no denominator. Each is screened against the FDA label (known vs unlabeled) on the drug pages; causality needs temporality, dose-response, plausibility and trial or cohort evidence.
Sources: openFDA FAERS pair statistics (OpenPV build 2026-09-14), FDA labels via openFDA, seriousness and death counts from openFDA count queries. Generated 2026-10-08. Not medical advice.