Alguns artigos ressaltam a instabilidade da molécula de glutamina em sua forma livre (l-glutamina) principalmente em contato com a agua. A glutamina se decompõe em ácido piroglutâmico e amônia, ambos tóxicos ao organismo.
"The excess glutamate at the neuron acts as a poison; at high enough levels, the nerves exposed to glutamate can be completely and permanently damaged, so that they are no longer capable of transmitting signals. Thus, while glutamate is a major component of the body, and an essential part of the nervous system, high levels localized in the nerve cells can be quite toxic, and this is readily demonstrated in animal models.
Glutamate levels in the blood increase slightly with high doses of supplemental glutamine administration (e.g., 15 grams in a single dose), but not with moderate doses (e.g., 5 grams in a single dose).
It is not known whether modification of dietary intake of glutamine and glutamate will have any effect on the degenerative brain disorders, since the mechanisms by which high glutamate content occurs in the brain may not be dependent on blood glutamate levels. However, the situation remains unclear and questions have been raised for the case that would most likely involve alterations in blood levels: weakness of the blood brain barrier after surgery, which would allow the blood glutamate to influence the central nervous system levels and potentially exacerbate the brain edema that occurs.
Until more is known about glutamine supplementation in relation to these brain diseases, it is recommended that patients who have nerve-damaging, chronic neurological diseases, such as ALS and multiple sclerosis, and those who have had recent neurological surgeries (such as for brain tumors) limit their intake of supplemental glutamine. A modest glutamine supplement level of about 5-10 grams/day is likely to have some benefit in relation to muscle wasting, immune responsiveness, or intestinal disorders, without promoting increased glutamate levels in the blood. Even 10 grams of glutamine is a small amount compared to the total body reserves that are already present, and studies show no significant glutamate increases in the blood after consuming such amounts. The higher levels of glutamine administration, commonly in the range of 15-30 grams per day, might be reserved for patients who do not suffer from these neurological diseases."