The short answer: It is not recommended.
The long answer: Pizza is defined as “a dish of Italian origin consisting of a flat, round base of dough baked with a topping of tomato sauce and cheese, typically with added meat or vegetables.” The ingredients used play a big part in determining if the pizza is safe for your dog to eat. Common ingredients such as cheese, cooked ripe tomatoes, and bell peppers are good for him. But on the flip side, the salt and oil used in the crust as well as toppings such as garlic, onions, and mushrooms are harmful for your dog.
What to do if your dog accidentally eats pizza: Determine how much your dog has consumed and what ingredients were in the slice he ate. Keep tabs on his condition.
Look out for pale gums, lack of energy or coordination, anemia, lethargy, drooling, nausea, weakness, vomiting, increased heart rate, labored breathing, discolored urine, and abdominal pain. If the pizza is known to contain ingredients that are toxic for him, take him to the veterinarian immediately.
In summary: Though it’s tempting to throw your dog a slice of greasy pizza, some of its ingredients and toppings may cause more harm than good to his body. If you really want to give him pizza, it would be best to make one on your own and top it with chopped vegetables and cooked meats that are guaranteed to be safe for him.