Can dogs eat coffee?
Toxic. No. Caffeine is a methylxanthine, the same class of compound as the theobromine in chocolate, and the chocolate thresholds are stated in combined methylxanthines for that reason.
How much is dangerous?
The chocolate calculator on this site works in total methylxanthines and covers caffeine alongside theobromine. Coffee grounds and used tea bags are the usual source, because dogs raid trash cans, and the caffeine content of grounds varies too much to publish one figure.
Why it does harm
Caffeine acts on the same pathway as theobromine — adenosine receptor blockade and increased intracellular calcium — producing cardiac and central nervous system overstimulation. The ASPCA groups coffee, caffeine and chocolate together for exactly this reason. Merck gives the half-life in dogs as 4.5 hours for caffeine against 17.5 hours for theobromine, so caffeine clears faster; that is a difference in duration, not a claim that either is milder.
What to look for
- Restlessness, pacing and hyperactivity
- Vomiting and diarrhea
- Panting and increased thirst
- Racing or irregular heartbeat
- Tremors and seizures at higher doses
What to do
- Call a vet with the source, the amount and your dog’s weight.
- Grounds and tea bags concentrate what is left after brewing, so a raided trash can is worse than a spilled mug.
- Caffeine pills and pre-workout powders are a different order of magnitude again. Treat those as an emergency.