Why late symptoms still matter for a 4 kg cat
Even though your cat seems fine now, three pills of sertraline for her size could still cause delayed reactions. SSRIs like this one can take time to fully affect the nervous system, and symptoms might not show until the drug reaches peak levels in her body. The fact she hasn't vomited yet is good, but neurological signs often appear later.
Watch for subtle changes like excessive grooming, hiding more than usual, or refusing food—these can precede more obvious signs. Confine her to a quiet room where you'll notice if she starts pacing or seems unable to settle. Late-appearing tremors or seizures would mean immediate vet care is needed, even days after ingestion.
The overheating risk you might not notice
Cats on SSRIs can develop dangerously high body temperatures without obvious panting. Feel her ears and paws periodically—if they're hotter than usual or she's lying on cool surfaces, serotonin syndrome might be affecting her temperature regulation. Normal cat body temperature ranges between 101-102.5°F; anything above 103°F warrants an emergency visit.
Check her gums too—bright red or pale gums when she's not exercising suggest circulation changes. Serotonin syndrome can cause blood pressure swings that aren't visible externally. If she's less playful or vocal than usual, that counts as a behavior change worth reporting to your vet.
Two days in—what cleared and what lingers
By now, most of the sertraline will have left her bloodstream, but its effects on brain chemistry can persist. The drug's half-life means trace amounts remain active in her system. What you're watching for now are secondary effects—has the medication altered her appetite or sleep patterns in ways that could lead to dehydration or weakness?
Offer small amounts of water frequently and note how much she drinks. Cats hiding discomfort may still use the litter box normally, so check for diarrhea or unusually small clumps. Any twitching during sleep could indicate neurological irritation that needs assessment.
When "fine" stops being fine
Some owners mistake lethargy for recovery when it's actually worsening toxicity. A cat lying quietly may seem better than one pacing, but if she's less responsive to sounds or treats, that's concerning. Test her awareness by rattling her favorite toy—she should at least turn her head.
Record her resting breathing rate (normal is 20-30 breaths per minute) when she's truly asleep, not just dozing. Rapid or shallow breathing this long after ingestion suggests complications. If she has any pre-existing heart conditions, even mild ones you've never treated, call your vet for advice now—don't wait for visible distress.
The step-by-step response, from the first minute to the vet visit, is in our Human Stress and Anxiety Medication Poisoning in Dogs and Cats emergency guide.