Along with multi-vitamins and creatine, glutamine is considered a foundational fitness supplement. Its benefits are also well known: better immune system, increased exercise recovery, and optimal muscle growth.
But how much is known about glutamine side effects?
Consider this statement from a user on the Bodybuilding.com forums:
“Ive recently taken glutamine for about 6 days, and now i am getting stomach problems causing a laxitive type effect.”
What harm, if any, does glutamine cause?
Possible Side Effects
Interestingly, a brief internet search quickly reveals not much is known about glutamine side effects.
WebMD, for example, states, “Glutamine is possibly safe for most adults and children when taken by mouth, but the potential side effects of glutamine are not known.”
However, just because potential glutamine side effects aren’t known, doesn’t mean there aren’t any. Glutamine may not be harmful in and of itself, but it might cause a reaction with a preexisting condition.
Pregnancy and breast-feeding: Glutamine has not been studied enough to determine its effects on infants. Consequently, experts recommend “stay on the safe side and avoid use.”
Hepatic Encephalopathy: (severe liver disease with difficulty thinking): Some believe glutamine worsens this condition. According to experts at the University of Maryland Medical Center, people with kidney disease, liver disease, or Reye Syndrome should not take glutamine.
Monosodium glutamate (MSG) Sensitivity: Monosodium glutamate is the salt form of glutamic acid. Although generally recognized as safe, it may cause an allergic reaction in some individuals. If you are sensitive to MSG, you may be sensitive to glutamine as well.
Mania: Mania is a mental disorder which may be worsened by increased glutamine levels.
Seizures: There is some concern glutamine increases the likelihood of seizures. Although this has not been fully tested on human subjects, animal study results are enough to warrant caution.
Cancer therapy: According to some laboratory studies, glutamine stimulates tumor growth. University of Maryland Medical Center experts explain, “Much more research is needed before it is known whether it is safe to use glutamine if you have cancer. If you are receiving chemotherapy, you should never add supplements to your regimen without consulting your physician.
Dangerous Side Effects
Because individual responses to supplements vary widely, there may be some side effects which require medical attention.
According to the Mayo Clinic, you should immediately check with your doctor if you experience blood in urine, chills, dizziness, and other serious side effects.
Additionally Kalpana Kumari, biotechnology and zoology expert, states excess glutamine intake leads to a rise in liver enzymes. Over-consumption of glutamine leads to psychological disorders due to excess of by-products glutamate and ammonia.
More Common Side Effects
While glutamine’s more dangerous side effects are intimidating, consumers should note these side effects are also rare.
Glutamine’s typical side effects are much milder in nature, and are usually the result of taking high dosages. These include cough or hoarseness, frequent urge to defecate, and straining while passing a stool.
Complaints from glutamine users on fitness forums typically involve upset stomach.
Bitter aftertaste can also be considered a common glutamine side effect. Most glutamine powders are flavorless, but have an unpleasant and bitter flavor when mixed with only water. This side effect may be avoided by mixing glutamine with a protein shake or smoothie.
Is Glutamine Safe?
While all the potential side effects of glutamine aren’t known, it is regarded as safe to use.
However, you should always err on the side of caution, and consult your doctor before using glutamine, especially if you are taking any medications or have a medical condition.
Remember that any dangerous glutamine side effects are less common, and glutamine is often consumed without any problems.
-  “Glutamine.” WebMD.
-  “Glutamine.” University of Maryland Medical Center.
-  Mebane AH. “L-Glutamine and Mania.” Am J Psychiatry. 1984 Oct;141(10):1302-3.
-  Eid T, Ghosh A, Wang Y, Beckström H, Zaveri HP, Lee TS, Lai JC, Malthankar-Phatak GH, de Lanerolle NC. “Recurrent seizures and brain pathology after inhibition of glutamine synthetase in the hippocampus in rats.” Brain. 2008 Aug;131(Pt 8):2061-70. doi: 10.1093/brain/awn133. Epub 2008 Jul 6.
-  “Glutamine (Oral Route).” Mayo Clinic.
-  Kumari, Kalpana. “Glutamine Side Effects.” Buzzle.com.
-  “http://forum.bodybuilding.com/showthread.php?t=433977&page=1”