Like any other supplement, consuming too much L-Glutamine can have some side effects. Thankfully, being a food derivative that the body itself produces, a slight increase does not do too much harm, apart from some minor side effects. The regular dosage for it varies depending on the reason for consumption. Its side effects are hearing problems, chest pain, sore throat, flu symptoms apart from nausea, vomiting, stomach pain. Also, check for swelling in the hands or feet, headache, tiredness, mild rash or itching. Dry mouth and runny nose are also something a few people might experience. The more severe effects could be liver disease along with difficulty in thinking or confusion, Mania, a mental disorder and Seizures in some cases.