This page is not veterinary advice. Paw Multiverse is not a veterinary practice. We cannot examine, diagnose or treat your animal. There are no medicines here, no doses, no home remedies and no treatment steps, on purpose. If your pet is unwell, has swallowed something, or has changed in a way you cannot explain, ring your vet or your nearest emergency clinic and let them decide. Full disclaimer.
This is the poisoning that starts with kindness. The dog is limping, the cat has been off its back leg for a day, and there is a packet of painkillers in the drawer that would sort a person out in twenty minutes.
It does not work that way, and the reason is specific rather than vague. Two enzyme systems that humans rely on to handle these drugs work differently in dogs and barely work at all in cats. That is what this page is about, along with the published thresholds and their limits.
If a tablet has already gone in, do not read to the end first. Use the tool, then ring.
Human painkiller exposure, against the figures MSD publishes
This reports what one veterinary reference publishes. It is not an assessment of your animal, it is not a reason to wait, and it will never tell you your pet is fine. Every result ends at a phone call.
It is printed on the blister strip or the box. Take the box with you.
Count the strip rather than trusting memory, and count part-chewed tablets as whole ones.
Figures read on 4 August 2026 from the MSD Veterinary Manual entry on toxicoses from human analgesics in animals. The source is named against every figure in the result. It was written for clinicians and not about your animal.
Ibuprofen: five bands, and the one that surprises people
The MSD Veterinary Manual entry on toxicoses from human analgesics, read on 4 August 2026, publishes five separate figures for ibuprofen in dogs. They are set out in the tool above and in the table below.
| Exposure | What MSD reports | Note |
|---|---|---|
| “8-16 mg/kg every 24 hours for 30 days” | Gastric ulceration or erosions | This is the band that catches people out, because it is far lower than the others and it is about repetition rather than a single accident. |
| “100-125 mg/kg” acute single dose | Vomiting, diarrhoea, nausea, abdominal pain, anorexia | A single event. |
| “175-300 mg/kg” | Renal failure | |
| Above “400 mg/kg” | CNS effects described as seizures, ataxia, listlessness and coma, plus renal and gastrointestinal signs | |
| Above “600 mg/kg” | Described as potentially lethal | |
| Cats, any of the above | “Cats are susceptible to ibuprofen toxicosis at approximately half the dose required to cause toxicosis in dogs.” | The word is approximately. It is not a precise conversion and we have not treated it as one. |
The first row is the one worth sitting with. It describes ulceration from a dose an owner might reasonably think of as small, given daily. That is not an accident scenario. That is somebody trying to help an arthritic dog with what is in the bathroom cabinet, which is a thing that happens constantly and which almost never gets written about, because emergency pages are written about emergencies.
MSD gives the mechanism: “NSAIDs inhibit cyclooxygenase (COX) enzymes (COX-1 and COX-2), thereby blocking the synthesis of prostaglandins.” Prostaglandins are not only inflammatory messengers. They also maintain the mucous barrier in the stomach and help regulate blood flow through the kidney. Block them for long enough and those two organs are the ones that pay.
Paracetamol: why cats are a different animal entirely
For paracetamol, MSD publishes a figure for dogs and two for cats. In dogs, “clinical signs of acute acetaminophen toxicosis are not observed unless the dose exceeds 100 mg/kg”. In cats, toxicosis occurs at “40-50 mg/kg”, and then the sentence that matters most on this page: “some cats, however, have been reported to develop clinical signs at 10 mg/kg”.
Ten. That is an order of magnitude below the canine figure, in an animal that weighs a fraction of a dog. A single ordinary human tablet is a serious event for a cat and the arithmetic in the tool above will show you why in about two seconds.
The reason is not mysterious. MSD states that cats “have low glucuronyl transferase activity and therefore have limited capacity for glucuronidation”. Glucuronidation is the main route by which the liver attaches a handle to certain compounds so the body can get rid of them. When that route is narrow, the drug goes down an alternative path that produces reactive metabolites, and those metabolites oxidise haemoglobin into methaemoglobin, which cannot carry oxygen. MSD notes that this “turns mucous membranes brown or muddy in color”.
We are not going to tell you to go and look at your cat’s gums and decide something. Colour changes belong to a vet with a light and a comparison. If you want to understand what a clinician is looking at and why, our page on gum colour explains the reasoning without turning it into a home test.
Correcting something this site used to say
An earlier version of this page said that paracetamol is lethal for cats at any dose. That is not what the source says, and overstating a danger is a way of losing an owner’s trust at the exact moment they need to believe you.
What MSD actually publishes is a toxicosis range of 40 to 50 mg/kg with clinical signs reported in some cats as low as 10 mg/kg. That is a terrifying figure without any embellishment. It also means the dose matters, which means the count matters, which means taking the box to the vet matters. “Any dose is lethal” invites an owner to conclude either that all is lost or that the warning is hysterical. Neither helps the cat.
human tablet swallowed
|
+------+------+
| |
ibuprofen paracetamol
| |
v v
COX-1 and limited glucuronidation
COX-2 blocked in cats (MSD)
| |
v v
prostaglandin reactive metabolites
synthesis falls |
| v
v haemoglobin oxidised
stomach lining to methaemoglobin;
and renal blood mucous membranes
flow affected brown or muddy (MSD)
| |
+--------+--------+
|
v
RING THE VET. BOTH BRANCHES.
TAKE THE BOX.
The counting problem
Every figure on this page is per kilogram, which means it depends on two numbers you are estimating under stress: what the animal weighs and how many tablets are gone.
Weight is the easier one. Use the last figure from the vet if you have it, and say it is from a while ago. Guessing high on weight makes the calculated dose look smaller, so if you are unsure, guess low on weight rather than high.
Tablets are harder. Count the strip rather than trusting your memory of how full the box was. Count a chewed fragment as a whole tablet, because you cannot know what was swallowed and what was spat out. If tablets were loose in a bag, assume the worst and say so. None of this is a reason to spend ten minutes reconstructing events. The box in your hand at the clinic is worth more than a precise number arrived at slowly.
What we could not source
We could not find, in the source we read, a level of either drug described as acceptable for either species. Every figure on this page is a level at which harm has been reported.
We could not find a precise cat conversion for ibuprofen. MSD says approximately half and we have left it at approximately half rather than doing the arithmetic and presenting it as a fact.
We could not source figures for other human analgesics such as naproxen, aspirin or the opioid-containing combination products, from the entry we read. If one of those is involved, the tool above cannot help you and the phone call matters more.
We could not source anything about timing of onset for either drug from this entry, which is a real gap. For the other poisonings on this site we can tell you how the hours unfold. Here we cannot, and we would rather say so than borrow a timeline from a weaker source.
We could not source any at-home step, and there is none on this page.
Printable: the two minutes before you ring
Ticks are held until you reload. Print it and keep it with the medicine box.
Have in your hand
Facts about the animal
Do not
Prevention, for later
Related pages
Other published thresholds, each with its source and read date attached: the grape and raisin checker, the onion and garlic checker, the xylitol checker and the chocolate calculator. The poison control directory and the poison control directory cover the rest of the house. If you are in the middle of it, my dog ate something, my cat ate something and the triage helper are the pages for right now, and before you call the vet will help you say it clearly.
