© Used with Peter Tsai's very kind permission.

There has been so much written on this topic both from those who are convinced that it causes significant incidence of various symptoms in people to those who simply blow it off. It's a situation without a satisfactory explanation to those whose experience is that they suffer when exposed to MSG. They often complain of a sense of being classified as  the "worried well".

MSG is really not unnatural. The manufacture of the product is synthetic for sure but its origins are natural. It occurs quite widely in a number of foods. The form of the compound be it the free acid glutamic acid or the substituted compound Mono-sodium Glutamate may occur spontaneously and is a product of the surrounding pH. The chemical characteristics are well known and easily looked up.

The "scientific evidence" seems to be overwhelmingly conclusive of the innocuous interpretation.  Various clinical studies have been conducted whereby volunteers admitting that they have a reaction to MSG and others stating that they had no reactions were included in various trials.

MSG was administered by various modes for example in capsules and by IV infusion. Placebos were set up scientifically and the trials were conducted by the operators without knowing either the status of the volunteers wrt sensitivity or whether or not an individual was being administered the placebo or the MSG.
The trials were conducted with full resuscitation facilities and specialist medical staff onboard. The trials were deemed ethical by the relevant ethics committees.  There was no direct input from vested commercial interests whatsoever. There may have been financial support by some of the suppliers of the MSG product but checks and balances made sure that there was no introduced bias (corruption if you like) in the design or the analyses of the data.
The analysis of the results showed no significant difference between the groups receiving MSG vs the placebo and no significant difference between the sensitised individuals and the non-sensitive individuals.
The conclusions \ suggest that no observable difference could be seen within the trial(s) conducted.

The compound is used extremely widely in Asia and other places. Most households would have a bottle of the condiment sitting there with the salt and fish sauce ready to add. It's used in salads and in cooked savoury dishes and enhances umami. It's not used as a thickener as some have suggested. The quantity generally used is in the 100 mgm range per 4 servings. There are very few stories of sensitivity around but at the same time there is the same awareness that it may not be innocuous and slowly Asian peoples, particularly urbanites, are not adding MSG to their own food preparations.  Restaurants are quite familiar with the request for "No MSG please" and have been for at least 10 years, even street stalls accept without hesitation this request. At the same time I have seen the waiter take the order but the cook add it to the food. In some cases the waiter is also the cook.

So what is the "Chinese Restaurant Syndrome" caused by? We simply don't know. It's looking as if MSG isn't the culprit but the weight of complaints of the various symptoms shouldn't be ignored, it has to be discovered. Maybe it's too early to throw out the MSG cause absolutely but it's not the likely single or only cause.