Maropitant (Cerenia) is, by volume of use, probably the antiemetic every small-animal practice reaches for most often. The FDA approved the injectable for the prevention and treatment of acute vomiting in dogs on January 29, 2007, added the cat indication on May 16, 2012, and added the intravenous route in January 2016. In nearly two decades on the market it has built a reputation as well tolerated — so when an owner asks whether Cerenia has side effects, the honest answer is that they are infrequent at the label dose, and that the public FDA data, read carefully, is mostly a lesson in how to separate a drug's real signals from the noise of the sick population it is given to.

To put real numbers on what actually gets reported, VetMedGuide analyzed the FDA Center for Veterinary Medicine (CVM) public adverse-event database, a June 2026 extract of 1.34 million reports. We identified reports naming maropitant and tabulated their reactions, outcomes, and history. The headline finding is counterintuitive and worth stating up front: the single most-reported reaction for an anti-nausea drug is vomiting. That is not a side effect of maropitant — it is a lack-of-efficacy signal, and understanding why is the key to reading every other number in the dataset.

The FDA's standard caveat applies throughout: spontaneous reports do not establish causation or true event rates, and "a report involving maropitant" means the drug was being given when the event was recognized, not that the drug caused it.

How we identified reports

Maropitant is recorded by active ingredient rather than brand, and the ingredient name "maropitant" maps cleanly to Cerenia (and its generic Emeprev). Working from the event-level file so each report is counted once, the June 2026 extract holds 15,784 reports naming maropitant — 11,243 in dogs and 3,514 in cats, with a small number listed as human exposures (201) or unclassified. The reports come in roughly equally from veterinarians (6,530), other health-care professionals (3,315), and owners (1,939), which matters: the data is not just post-marketing surveillance from clinics, it is owner-driven too.

Reporting has climbed steadily across the drug's life — from a few hundred reports a year in 2007–2011 to over 1,700 in 2024 and 1,956 in 2025. That curve tracks adoption rather than any safety change: more practices using a drug in more patients produces more reports, including more reports that have nothing to do with the drug.

Why vomiting is the #1 reaction, and what the death count means

The top reported reactions across all reports are vomiting (3,817), lethargy (3,304 across two coding variants), anorexia (2,034), diarrhea (1,846), and then death by euthanasia (1,685) and death (1,506). Outcomes were recorded as euthanized in 1,522 reports and died in 1,779 — about 3,301 reports with a fatal outcome, or roughly 21% of the total.

Read at face value that looks alarming for a "safe" drug. It is not, once you account for who gets maropitant. This is a drug given to animals that are already vomiting — patients with pancreatitis, kidney disease, gastrointestinal obstruction, toxin ingestion, parvoviral enteritis, sepsis, or chemotherapy-induced nausea. Those underlying diseases are what kill the animal; maropitant is just present in the chart. The vomiting "reaction" is the original symptom continuing because the underlying cause is still active — a treatment-failure marker, not an adverse effect. The FDA codes "lack of efficacy" separately, and it appears in 1,399 reports, but the residual vomiting that does not get coded that way tells the same story.

This is the central caution for anyone reading spontaneous-report data on a supportive-care drug: background disease swamps drug signal. A drug given to the sickest patients will always accumulate death and serious-illness reports that say more about the patients than about the drug. The serious-flag rate — 7,473 of 15,784 reports marked serious, about 47% — reflects the same thing. It does not mean maropitant causes a serious event half the time.

The real drug-attributable signals

Strip away the disease noise and the reports that line up with drug harm are exactly what the label already describes. The most clinically important is injection-site reactions: 538 reports of injection-site pain, 268 of injection-site swelling, plus smaller numbers of abscess (79), lump (76), necrosis (68), and bruising. The Cerenia label lists "pain/vocalization upon injection" as the most frequent post-approval event in dogs and "pain/vocalization upon injection" among the top events in cats, and the cat-target-safety study submitted for the 2012 approval found that subcutaneous maropitant at label doses causes injection pain and that the sting is dose-related — higher motion-sickness doses and colder (refrigerated) injectable sting more, which is why warming the syringe before injection is standard practice.

The other on-label signals are all present in the data: lethargy and sedation, anorexia and reduced appetite, ataxia, hypersalivation, and rare allergic or anaphylactoid reactions. Fever (881 reports) and elevated liver enzymes (ALT elevated in 1,207 reports, ALP in 793) appear too, but in a vomiting population these are more plausibly part of the underlying illness than maropitant effects; the label notes hepatic changes in lab studies and recommends caution in liver disease, which is the prudent read.

Cat-specific points

Cats make up about one in five maropitant reports (3,514 of 15,784), and their reaction profile is similar to dogs but with less diarrhea: vomiting (669), anorexia (507), lethargy (444), and then the death-and-euthanasia outcomes reflecting the same sick-population effect. The cat-specific safety story is injection pain — the FDA's cat approval study explicitly documented that subcutaneous maropitant causes pain at the injection site and increased the need for restraint, which is why many clinicians give the cat dose subcutaneously with the injectable warmed, or use the slower IV route where appropriate. Injectable maropitant is the only FDA-approved form for cats; the tablet is approved for dogs only and is used extra-label in cats.

What to take into the exam room

• Cerenia's safety reputation holds. The reports that look scary — the vomiting and the death counts — are confounded by the sick population the drug is given to, not evidence of drug harm at label doses.
• Manage injection-site sting proactively, especially in cats and at the higher motion-sickness dose. Warm the injectable before subcutaneous administration; this single step addresses the most common real, drug-attributable complaint.
• Persistent vomiting after maropitant is a signal to keep looking, not to re-dose. The drug controls nausea well; if it is not working, the underlying cause (obstruction, pancreatitis, metabolic disease) needs workup.
• Use caution in liver disease, per label, and watch the rare allergic/anaphylactoid reaction — both are consistent with the post-approval data.

Sources

• FDA CVM, animal adverse-event database (public extract, June 2026); analysis by VetMedGuide. The FDA cautions that spontaneous reports do not establish causation or true event rates. https://www.fda.gov/animal-veterinary/safety-health/reporting-animal-drug-and-device-side-effects-and-product-problems
• Cerenia (maropitant citrate) injectable solution prescribing information, DailyMed (post-approval adverse events for dogs and cats; injection-site reactions; "cases of death (including euthanasia) have been reported"). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6aeda328-97c9-4868-8ecb-b3a4dcdbc0a0
• Cerenia (maropitant citrate) tablet prescribing information, DailyMed (post-approval experience revised May 2019; ineffectiveness and death reports). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3bc065ce-09d6-4131-a5a0-dca3909e0bc8
• FOI Summary, NADA 141-263, Cerenia (maropitant citrate) injectable solution, original approval January 29, 2007 (dogs). https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/818
• FOI Summary, NADA 141-263 supplemental approval, Cerenia injectable for cats, May 16, 2012 (cat target-animal safety: injection pain and injection-site reactions at label doses). https://downloads.regulations.gov/FDA-2012-N-0002-0017/attachment_1.pdf
• FOI Summary, NADA 141-263 supplemental approval, Cerenia injectable IV route for dogs and cats, January 11, 2016. https://downloads.regulations.gov/FDA-2016-N-0002-0007/content.pdf