Some people say that food with MSG, a flavor enhancer, gives them headaches. This idea started with one doctor's letter in 1968.

Later, scientists tested it carefully. People did not know if they were getting real MSG or a fake. When people ate MSG with food, it did not cause problems. Many foods, like tomatoes and cheese, already have the same natural substance.

The link between MSG and headaches began in 1968, when a doctor wrote a short letter to a medical journal. He described feeling numb and weak after eating at Chinese restaurants and suggested several possible causes, including MSG. Many similar personal stories followed, but they were not scientific tests.

In 2000, researchers carried out a double-blind study with 130 people, all of whom believed they reacted to MSG. Neither the participants nor the researchers knew who received MSG and who received a placebo. Some people reported symptoms after taking large amounts of MSG without food, but the reactions were not repeated in later tests. When MSG was taken with food, no reactions were found.

The link between monosodium glutamate and headaches can be traced to a 1968 letter in a leading medical journal, in which a physician described numbness, weakness, and palpitations after meals at Chinese restaurants and listed MSG among several possible causes. A flood of anecdotes followed, yet anecdotes cannot separate a substance's effects from expectation. Double-blind, placebo-controlled trials address this problem. In a multicenter study published in 2000, 130 participants, all of whom believed they were sensitive to MSG, received either MSG or a placebo without knowing which.

Large doses taken without food produced slightly more symptoms than the placebo, but the responses were infrequent, inconsistent, and not reproducible on retesting; when MSG was taken with food, no reactions appeared. A 2016 systematic review of headache studies found no difference when MSG was consumed with meals, while noting that positive results from studies using concentrated solutions may reflect failed blinding, because MSG's distinctive taste can reveal it. One author of that review belonged to a glutamate industry group, a potential conflict of interest. Meanwhile, the U.S. FDA classifies MSG as generally recognized as safe.