Both you and your dog manufacture your own glutamine, a "conditionally essential" amino acid. The National Institutes of Health defines a conditionally essential amino acid as one that is essential only in times of illness and stress. If your pup is under the weather, your vet may recommend a glutamine supplement to give him a boost.
Getting a Boost from Glutamine
Though it's only conditionally essential, glutamine plays a part in maintaining a healthy immune system and digestive tract. Sometimes a dog's glutamine reserves become depleted -- infection, trauma, strenuous exercise and surgery are some common causes of glutamine depletion -- and a glutamine supplement can be just what the vet orders. Because of its beneficial effects on the digestive tract, the vet may recommend a glutamine supplement for a dog with digestive issues such as inflammatory bowel disease. As well, it's sometimes helpful for dogs undergoing treatment for cancer, as the supplement can help with gastrointestinal side effects of treatment, as well as can potentially help boost the immune system.
Glutamine is not recommended for a dog with epilepsy, as it may work against epilepsy medication. Though a prescription is not required for glutamine, you should discuss the supplement with your vet -- supplements aren't highly regulated, so your vet will be able to advise you on dosage requirements and may recommend a reputable brand.