There are a lot of foods and drinks that are outright dangerous for dogs, chief among them chocolate (the very first thing your vet warns about, in fact), coffee, and any caffeinated drink… like tea, for example. Thus, the answer to the question, can dogs drink tea, is no; but some might say that they have dogs that drink tea, and they’re none the worse for wear. These owners are ignorant. It’s like asking if the sky is blue. At first, you’d think it’s a commonsensical question, until you realize the sky changes colors depending on the time of day. It’s the same with tea. You “can” make your dogs drink tea and have him survive, but all-in-all, as the sky is “generally” blue, tea is “generally” dangerous.
It Depends…? No, You Simply Shouldn’t
As far as your vet is concerned, the answer is still, “No.” There are pet owners who make their dogs drink tea, especially cold tea. However, vets advocate against this, and it’s more than just the fact that tea can stain teeth; tea has harmful caffeine in it. The same way certain dogs are fed milk chocolate (not as dangerous as pure chocolate, but still dangerous), it’s also not advisable to feed dogs tea, whether it’s green tea or black tea.
Caffeine when consumed in huge quantities is fatal to the dog, and you might have to feed them some sort of vomiting medicine to get that caffeinated drink or substance out before they metabolize it; after all, there’s no antidote to it. If you’re adventurous and ignorant, you “can” feed your dog non-pure chocolate and tea, but like with smoking, that’s just asking for trouble.
Caffeine poisoning symptoms include the following: Fits, muscle tremors, heart palpitations, rapid breathing, restlessness (like in a sugar rush), and bleeding (it’s especially fatal once bleeding occurs, or it may already be too late). Tea doesn’t contain as much caffeine as coffee, cocoa, cola, certain medicines and drugs, beans, and grounds, but why risk it? It’s better to err on the side of caution.