Vomiting and diarrhea may come together as a pair of gastrointestinal problems, or they may happen separately. Dogs with an upset stomach sometimes eat grass. Observe what type of grass your dog is eating. Dogs that just wanted to chew 'salad' prefer new grass, while older, tougher grass is more likely to help the dog vomit.

Diarrhea may smell and look different depending on the cause. Puppies with parvo may pass some digested blood, which gives their diarrhea a distinctive odor. A dog with pancreatic problem that is not digesting fats well may have grayish, smelly diarrhea. No matter how gross and disgusting the stuff is, you should save a sample for your vet. A fecal sample cna help your vet identify parasites, test for diseases such as parvovirus, and check for blood in stool. A small amount is all that is needed.
Chronic diarrhea (lasting more than a week) can be a sign of a metabolic disease such as pancreatic insufficiency or can be related to cancer. Work up for a chronic diarrhea problem can require blood work, special X-rays and possibly biopsies and endoscopy (examination of the stomach and intestines with a special scope).

Some vomiting triggered in the brain centers where nausea originates. Dogs that get car sick have this type of vomiting. Most vomiting originates in the gastrointestinal tract, usually the stomach. If your dog eats something bitter or irritating, his body may want to get rid of it, causing the dog to vomit. Illnesses that disrupt the tract, such as parvo, will also cause vomiting. Vomiting can also occur as part of a generalized problem such as a neuromuscular disease. Dogs may vomit occasionally just from a mild upset stomach. Some medications are designed to stimulate vomiting when your dog has eaten a foreign object or something unhealthy such as chocolate or certain poisons. Always check with your vet before making your dog throw up. There are certain poisons that do more damage if they are vomited back up, such as petroleum distillates and certain acids and alkalis.

f your dog vomits once or twice but can keep water down and feels fine otherwise, you can keep an eye on him at home. Holding off on food for a day or so may help you dog recover from vomiting and diarrhea. He needs fluids, though, so if he can't keep water down, you need to contact your vet. This is even more crucial in puppies and older dogs. After a day with no food, you should start back with a bland diet and gradually work over to your dog's regular diet. Your vet can provide special prescription bland foods or guide you to homemade substitutes.