The NOW Foods L-glutamine is one of the products that we recommend from a brand that we trust. In the Dog Cancer Survival Guide, Dr. Dressler states that glutamine can be beneficial for your dog as it ensures that your dog has the necessary fuel to rebuild the tissues that were injured from vomiting and diarrhea. Glutamine can correct these deficiencies and it ensures that your dog heals as quickly as possible.
If your dog has brain cancer, do not give them glutamine (it actually feeds your dog's brain cancer growth BEFORE it gets to your dog's normal tissues!).
You should always check with your vet if your dog is having medical issues and before using glutamine as it is a potent supplement and it's not safe for all dogs.
You may also want to review page 147 in the Dog Cancer Survival Guide, for information on glutamine and the correct dosage for your dog! :-)