Antidepressants (SSRIs, SNRIs, tricyclics)

How Much Is Dangerous

Varies considerably by the specific drug and formulation involved, but even a single dropped or accessible pill represents a meaningful dose for a small cat and should be treated as a genuine exposure requiring veterinary attention, not a trivial event to simply monitor at home.

Symptoms

• Agitation, vocalization, or unusual restlessness beyond the cat's normal behavior
• Dilated pupils
• Muscle tremors
• Elevated body temperature
• Increased heart rate
• Vomiting
• Seizures in significant overdoses, particularly associated with tricyclic antidepressants specifically
• Abnormal heart rhythm, especially with tricyclic antidepressants given their additional cardiac-conduction effects

Time to Symptoms

Often within 1–4 hours of ingestion, though the exact timeline and symptom pattern varies somewhat depending on the specific drug class and formulation (immediate-release versus extended-release) involved.

First Aid Steps

• Contact a veterinarian or emergency animal hospital promptly
• Bring the medication packaging so the exact drug, strength, and formulation can be identified — this genuinely changes both the urgency and the specific treatment approach
• Keep the cat in a calm, quiet, dimly-lit space while arranging transport to care, since sensory overstimulation can measurably worsen serotonin syndrome signs in the interim

What Not To Do

• Do not store medication in easily-knocked-over weekly pill organizers or leave bottles open on nightstands or bedside tables — this is a very commonly reported real-world source of accidental pet ingestion across many medication categories, not just antidepressants specifically
• Do not wait to see if mild agitation resolves on its own — this class of medication is well known for being able to progress from mild to severe relatively quickly, and early veterinary involvement changes the trajectory

Veterinary Treatment

Decontamination if caught early, IV fluids, active cooling measures if body temperature is significantly elevated, medication to control agitation and seizure activity, and continuous ECG (heart rhythm) monitoring — particularly important for tricyclic antidepressant ingestions given their specific cardiac effects. Cyproheptadine, a serotonin antagonist medication, may be used specifically to counteract significant serotonin syndrome when it develops.

Toxic Compound

SSRIs and SNRIs work by increasing serotonin activity within the nervous system; an overdose amplifies this effect into serotonin syndrome — a state of excessive serotonergic activity producing agitation, dangerously elevated body temperature, and cardiovascular effects acting together. Tricyclic antidepressants carry an additional, separate concern: direct effects on cardiac electrical conduction and an increased seizure risk beyond what's seen with newer antidepressant classes. Notably, some antidepressant formulations are reported to be unusually palatable to cats — a genuinely unfortunate combination with a medication class that carries real toxicity risk, and part of why accidental ingestion of this drug category is reported more often than might be expected given how these medications are typically stored.