A review article published in Assumption University Journal of Technology claims that consumption of monosodium glutamate (MSG) can lead to a variety pf health conditions.

David Tin Win at Assumption University Bangkok, Thailand lists in his review the health conditions that are influenced by MSG including 

Cardiac

Arrhythmias 

Extreme rise or drop in blood pressure 

Rapid heartbeat (tachycardia), Angina 

Circulatory

Swelling Muscular 

Flu-like achiness, Joint pain, Stiffness 

Neurological

Depression

Dizziness, Light-headedness, Loss of balance 

Disorientation, Mental confusion 

Anxiety, Panic attacks 

Hyperactivity, Behavioral problems in children 

Lethargy, Sleepiness, Insomnia 

Migraine headache. Numbness or paralysis 

Seizures, Slurred speech 

Gastrointestinal

Diarrhea 

Nausea/vomiting 

Stomach cramps 

Irritable bowel, Bloating 

Respiratory

Asthma, Shortness of breath 

Chest pain, Tightness 

Runny nose, Sneezing 

Skin

Hives or rash. Mouth lesions 

Temporary tightness or partial paralysis 

(numbness or tingling) of the skin Flushing 

Urological

Swelling of prostate Nocturia 

Visual

Blurred vision, Difficulty focusing

How to avoid MSG?

MSG renders a unique taste called umami (the fifth taste).   MSG may not show up in the ingredient list but still can be found in the food you eat.  As long as the food you eat tastes savory (yammy), it more likely than not contains MSG.  So if you want to avoid ingesting too much MSG, avoid foods that taste too yammy.