While dogs can have basil to enjoy health benefits discussed above, basil shouldn’t replace healthy dog food. In fact, basil should only be used to supplement dog food. What's more, it should be given sparingly; otherwise, your dog can suffer some of the side effects discussed below: Digestive problems: As mentioned above, basil should be given in small quantities. Giving your dog too much herbs can cause digestive system problems like diarrhea, stomach upset, and vomiting. This is a common side effect due to dog's sensitivity towards herbs. Skin problems: Your dog can develop skin problems because of eating too much basil. If you enjoy feeding your dog human foods and you put a lot of basil in your food, your dog can suffer skin problems like itchiness. Allergy effects: Some dogs are allergic to basil and herbs in general. As a result, some precaution is necessary when giving your dog basil for the first time. Basil is common in human foods. If you feed your dog basil on its own or as part of a snack or bite of human food, observe them for allergies. Common effects of allergies in dogs include sneezing, swelling, hives, diarrhea, vomiting and itchy ears. Allergies should be reported immediately to your vet. Severe side effects like breathing problems can be lethal to your dog. It's worth noting that the digestive system of dogs is designed for a carnivorous diet. Dogs that eat a lot of plant-based foods tend to suffer serious problems.