🚨 If symptoms are present — go to emergency vet NOW. ASPCA Poison Control: (888) 426-4435 (24/7)

🧠

HIGH RISK

Antidepressant Poisoning in Dogs

Antidepressants — including SSRIs like fluoxetine (Prozac) and sertraline (Zoloft), SNRIs like venlafaxine (Effexor), and tricyclic antidepressants (TCAs) like amitriptyline — are among the top 10 most common toxicoses reported in dogs. These medications can cause a dangerous condition called serotonin syndrome, as well as cardiovascular effects. Any ingestion should be treated as an emergency.

✓ Vet ReviewedReviewed by Dr. Mara Voss, DVM · Updated 2026

📞 Call ASPCA Poison Control — (888) 426-4435

A $95 consultation fee applies to ASPCA Poison Control calls.

⚡ Immediate Actions

1Call your vet or ASPCA Poison Control (888) 426-4435 immediately.
2Note the exact medication name, strength, and number of pills missing.
3Do not induce vomiting without professional guidance — some TCAs have seizure risk.
4Monitor body temperature — hyperthermia is a serious sign of serotonin syndrome.
5Go to an emergency vet immediately if your dog is seizing, collapsing, or has a very high temperature.

Symptoms & Timeline

Mild serotonin effects

Excess synaptic serotonin overstimulates 5-HT1A and 5-HT2A receptors throughout the nervous system. Stimulation of 5-HT2A receptors in the spinal cord and brainstem drives muscle hyperexcitability (tremors), while autonomic 5-HT effects dilate pupils and accelerate heart rate.

Restlessness and agitation
Dilated pupils
Vocalization
Muscle tremors
Rapid heart rate

Moderate (serotonin syndrome)

As serotonin excess intensifies, thermoregulation breaks down — skeletal muscle rigidity generates massive metabolic heat without the normal homeostatic cooling response. Hyperthermia above 104°F (40°C) damages cells directly. GI serotonin receptors (particularly 5-HT3 and 5-HT4) drive the nausea and diarrhea.

Hyperthermia (elevated body temperature)
Rigid muscles
Incoordination
Vomiting and diarrhea

Severe

In TCA ingestion, the tricyclic molecule blocks fast sodium channels in myocardial cells, widening the QRS complex and creating conditions for fatal ventricular arrhythmias. SSRIs at extreme doses can also trigger seizures through serotonin-mediated cortical hyperexcitability. Hyperthermia from sustained muscle rigidity precipitates multi-organ failure.

Seizures
Cardiac arrhythmias (especially with TCAs)
Collapse
Respiratory failure

How Antidepressants — SSRIs, SNRIs, TCAs (Prozac, Zoloft, Effexor, Elavil) Affects Dogs

SSRIs and SNRIs block the reuptake of serotonin in nerve synapses, increasing serotonin levels. In dogs, excess serotonin causes serotonin syndrome — a potentially life-threatening constellation of neuromuscular, autonomic, and cognitive abnormalities. TCAs also block norepinephrine reuptake and have significant anticholinergic effects, plus sodium channel blocking effects in the heart, which can cause dangerous arrhythmias even in small doses. Cats are more sensitive to these drugs than dogs, but dogs are still at significant risk.

What Your Vet Will Do at the Clinic

Antidepressant toxicosis is managed by addressing three simultaneous threats: excess serotonin, hyperthermia, and (for TCAs) cardiac arrhythmias. Cyproheptadine, an antihistamine with serotonin antagonist properties, competes with serotonin at 5-HT receptors, attenuating the neuromuscular and autonomic storm. Methocarbamol or diazepam relaxes the rigid muscles, directly addressing the primary heat source. Active cooling — ice packs, cool IV fluids, fans — is critical when body temperature exceeds 104°F, since hyperthermia above 108°F causes irreversible neurological damage. For TCA poisoning, sodium bicarbonate is the antidote mechanism: alkalinizing the blood shifts sodium channel kinetics, reducing TCA binding and narrowing the dangerous wide QRS complex on ECG. Activated charcoal is high priority for TCAs because of their prolonged GI absorption window.

Step-by-step protocol:

1Decontamination: induced emesis if recent ingestion and dog is not yet symptomatic
2Activated charcoal — especially important for TCAs
3Cyproheptadine (serotonin antagonist) for serotonin syndrome management
4Muscle relaxants (methocarbamol) for tremors and rigidity
5IV fluids and temperature regulation (cooling if hyperthermic)
6Cardiac monitoring: ECG essential for TCA ingestion
7Sodium bicarbonate for TCA-induced cardiac arrhythmias
8Seizure management with diazepam or phenobarbital as needed

Frequently Asked Questions

My dog ate my Prozac (fluoxetine). How dangerous is it?

Fluoxetine toxicity in dogs depends heavily on the dose and your dog's weight. SSRIs have a relatively wide therapeutic index but can still cause serious serotonin syndrome at overdose levels. Call ASPCA Poison Control or your vet with the mg strength and how many pills may have been ingested.

What is serotonin syndrome in dogs?

Serotonin syndrome is a potentially life-threatening reaction caused by excess serotonin activity. Symptoms include muscle rigidity, tremors, hyperthermia (fever), rapid heart rate, agitation, and in severe cases seizures and collapse. It requires emergency treatment.

Are tricyclic antidepressants (TCAs) more dangerous than SSRIs for dogs?

Yes, TCAs (amitriptyline, clomipramine, doxepin) are generally more acutely dangerous than SSRIs in dogs due to their additional anticholinergic effects and direct cardiac toxicity. TCA poisoning can cause fatal heart arrhythmias and should always be treated as a critical emergency.

🛡️ Emergency vet bills average $1,500–$5,000

Most US dog owners pay out of pocket. Pet insurance can cover 70–90% of unexpected emergency costs.

Lemonade Pet — Get a Quote Spot Pet Insurance

Sponsored · EverDogParent earns a referral fee if you purchase a plan

🐾