Litter Box Problems - Marking, Toileting and Medicine

Because something has changed. The awkward part is that the thing which changed is very often not the thing the household assumes, and the published guidance starts in a place most people get to last.

If the cat in question is a kitten who has only just arrived, read this alongside New Kitten: The First 30 Days. Most of the problems described below are prevented rather than fixed, and they are prevented in the first month by tray arithmetic, placement and substrate - which is where that page starts.

Rule one, and it is not negotiable

Merck's chapter on behaviour problems of cats puts it without qualification: "With house soiling in cats, the first step is always to exclude medical problems." Read 4 August 2026. It adds that any condition affecting urine control, or the ability to reach the box, can contribute.

That sentence exists because house soiling is not a behaviour with a behavioural cause by default. It is a sign with a long differential behind it. Several of the things on that list are painful. One of them, urinary obstruction in a male cat, is fatal within a day or two.

It also explains why household troubleshooting so often fails. A new litter, a moved tray, a second box: all sensible responses to a preference problem, all useless for a cat that hurts when it urinates. Worse than useless, in fact, because they consume the days in which something else is developing.

Rule two: decide which of the two behaviours you are looking at

Merck separates them explicitly: "Urine marking must be differentiated from undesirable toileting." Read 4 August 2026. It distinguishes them on three features. Posture, standing with the tail up for marking against squatting for toileting. Volume, a small amount against a full void. Surface, vertical against horizontal.

This distinction is worth more than anything you could buy, because the two problems share almost nothing beyond the smell. Marking is communication. Toileting outside the box is either a rejection of the box or an inability to use it. Treat one as the other and you will run the same failed experiment for months.

WHICH ONE IS IT

  Find the deposit. Ask three questions.

  1. Posture, if seen?   standing, tail up    -> marking
                         squatting            -> toileting

  2. How much?           a small amount       -> marking
                         a full void          -> toileting

  3. What surface?       vertical: wall,      -> marking
                         door, sofa side
                         horizontal: floor,   -> toileting
                         carpet, bed, bath

  Two out of three pointing the same way is usually enough to
  describe it accurately on the phone. Accuracy is the point.

  Merck, behaviour problems of cats, read 4 August 2026.

Rule three: punishment pushes the wrong way

Merck is unusually direct: "Positive punishment is contraindicated because it increases fear and anxiety in an already anxious animal." Read 4 August 2026.

Notice the phrase already anxious. That is not a general appeal to kindness. It is a claim about the population of cats that soil indoors. If anxiety is part of the cause, adding fear is not a neutral intervention that happens to fail. It is an intervention that pushes in the wrong direction.

There is a second, more mechanical problem. A cat scolded near its tray has learned something about the tray, not about the carpet. Anything unpleasant delivered in the vicinity of the box teaches avoidance of the box.

The box itself, using the specifications Merck gives

Where Merck is specific about the environment, the specifics are physical rather than pharmaceutical, and we are happy to reproduce them, because they describe furniture.

Feature	What Merck says
How many	"At least two litter boxes should be available in every core area where cats that get along are housed"
How big	The box should be "at least 1½ times the length of the cat from tip of the nose to base of the tail"
How clean	"Litter boxes should be hygienic and scooped at least daily"
Where	"Away from food and water, quiet"
Which litter	Determine "which litter type and box type are preferred by offering the cat choices"

All read 4 August 2026. Two of those rows deserve comment.

The size specification is the one most households fail without knowing. Trays are designed to fit bathrooms, not cats. Measure the cat from nose to tail base, then measure the tray against that figure. A large cat in a standard tray is being asked to turn, dig and cover in a space it does not fit in, and its objection is entirely reasonable.

The phrase "in every core area" is doing quiet work too. It is not a total for the house. It is a statement about each region a cat treats as its own, which in a house with stairs is not the same as one utility room with two trays lined up in it.

The preference trial, which is the only real experiment here

Merck does not recommend a litter type. Its method is to let the cat tell you, by "offering the cat choices". That is genuinely testable, and hardly anyone runs it properly, because they change one thing every few weeks and lose track of what they changed.

The log below runs it as a side by side comparison instead. Put out two trays at once, differing in exactly one property, and record which gets used. Then move to the next property. It is slow and unglamorous and it produces an answer rather than an opinion.

The map is more useful than it sounds

Those last two rows are the ones people skip and later wish they had not. A dated map turns an impression into evidence, and it answers the questions a vet or a behaviourist will ask and you will otherwise have to guess at. Always the same room. Near a window. Near the door the other cat uses. Started the week the builders arrived, or the week the tray was moved.

Merck names stress and social conflict among the contributors, and conflict between cats expresses itself spatially. A cat being blocked from a corridor does not file a complaint. It relieves itself somewhere else, and the somewhere else is the clue.

What we could not source

• Covered against uncovered. Merck offers a method, not a verdict. We found no statement declaring either better, so the trial treats it as a variable to test.
• Cleaning products for soiled areas. Enzymatic cleaners are recommended everywhere online. Nothing we read named a product type, so this page names none.
• Litter depth. Not addressed. Included as a trial variable rather than a recommendation.
• Liners, mats and self cleaning trays. Not addressed at all.
• Medication. Merck's behaviour material includes pharmacological options. We have named none and will not. That is a prescribing conversation with a vet who has examined the cat.
• Timeframes. Nothing on how long a trial should run or how long improvement takes.
• Cats that were never reliable. The guidance is framed around a change in behaviour. A cat that has never used a box consistently may be a different problem, and we found nothing to build that section on.

Questions people actually ask

He is doing it out of spite because I went away.

Nothing in the veterinary material supports spite as a mechanism, and the framing does real harm, because it leads directly to punishment, which Merck says is contraindicated. Absence, disruption and a changed routine are all plausible stressors, and stress is named as a contributor. That is a different sentence, and a more useful one.

She is spayed, so it cannot be marking.

Merck does not restrict marking to entire cats, and the three tests it gives, posture, volume and surface, make no mention of neutering. Use the tests rather than the assumption.

Two cats, three trays. Is that enough?

Merck's phrasing is at least two boxes in every core area where cats that get along are housed. The operative word is area, not house. And the qualifier about cats that get along carries an implication about cats that do not.

It only ever happens on the bed.

Horizontal surface, and if it is a full void that points at toileting rather than marking on Merck's criteria. It also has a less comfortable reading, because bedding is soft, absorbent and smells strongly of you, and cats that are unwell or frightened seek exactly that. Tell the vet where, not just that.

Should I shut her in one room with a tray?

We are not giving you a confinement protocol. We found none we could quote, and it is the kind of intervention that is either the correct first step or a serious mistake depending on the cause. Ask the vet, who by then will have ruled the medical causes in or out.

How long before I know whether a change worked?

No source we read gave a figure, so neither will we. What we will say is that the dated map is what makes any answer possible. Without it, three weeks of slow improvement and three weeks of nothing feel identical in hindsight.

Related pages

Other cat material here: onions and garlic, both of which describe a delayed poisoning households rarely connect to a meal, and grapes, an honest account of very thin evidence. Plants that share a room with a cat: spider plant and snake plant. Food index: can cats eat, or the whole set at can my pet eat. If something is urgent, find an emergency vet.

How we sourced this page

One document, fetched and read on 4 August 2026. We are naming it as a single source deliberately, because implying broader backing than we have would be the same failure we criticise elsewhere on this site.

• Merck Veterinary Manual, Behavior Problems of Cats. Used for the instruction to exclude medical problems first, the differentiation of marking from toileting on posture, volume and surface, the contraindication of positive punishment and its stated reason, the box number, size, hygiene and location specifications, the method of determining litter preference by offering choices, and the naming of stress and social conflict as contributors.