Does MSG give you headaches? Only in the studies where you could taste it

Claim

MSG AND HEADACHES?

Catch

NOT PROPERLY BLINDED

Verdict

MOSTLY A NON-EVENT

The evidence: Obayashi and Nagamura published "Does monosodium glutamate really cause headache? A systematic review of human studies" in the Journal of Headache and Pain in 2016 (17:13; DOI 10.1186/s10194-016-0639-4). It included every human study of MSG administration and headache incidence, and — this is the key methodological move — separated studies where MSG was given with food from studies where it was given without food. The reason matters: glutamate kinetics differ substantially between the two conditions, and there is prior evidence that the symptom pattern itself differs.

The finding, in the review's own words: "Of five papers including six studies with food, none showed a significant difference in the incidence of headache except for the female group in one study. Of five papers including seven studies without food, four studies showed a significant difference."

The catch: "Many of the studies involved administration of MSG in solution at high concentrations (over 2%). Since the distinctive MSG is readily identified at such concentrations, these studies were thought not to be properly blinded. Because of the absence of proper blinding, and the inconsistency of the findings, we conclude that further studies are required to evaluate whether or not a causal relationship exists between MSG ingestion and headache."

That is the whole story in three sentences. Headaches showed up in the trials where participants could taste the MSG and therefore knew they had been given it. They did not show up in the properly blinded trials where the MSG was mixed into food.

The supporting studies point the same way. A 2013 double-blind crossover study (14 healthy subjects, 150 mg/kg MSG for 5 days) did find more headaches on MSG (8 of 14 vs 2 of 14 on placebo, P = 0.041) — but that dose was delivered in a strongly flavoured solution, and the authors noted it produced a distinct "MSG symptom complex" of headache, sweating and tingling. A 1997 double-blind challenge study in 61 people who self-identified as MSG-sensitive found 36.1% reacted to MSG versus 24.6% to placebo — a difference that was not statistically significant (P = 0.324) — with an apparent threshold dose of about 2.5 g. And the 2016 review notes that the "symptom complex" is real for the minority who experience it; what is contested is how many people that is, and whether ordinary food-level exposure produces it.

Bottom line: if you get a reaction to MSG, that is real and worth taking seriously. But the honest summary of the human literature is that properly blinded, food-based studies do not reproduce the syndrome, and the studies that do are ones the reviewers judged to be unblinded. Nobody has ever said MSG in food is dangerous for everyone — that is a different claim, and it is not what the evidence shows either way.

SOURCES

1. Obayashi Y, Nagamura Y. "Does monosodium glutamate really cause headache? A systematic review of human studies." J Headache Pain. 2016;17:13. DOI: 10.1186/s10194-016-0639-4. PMID 27189588. PMCID PMC4870486.
2. Shimada A, Cairns B, Vad N, et al. "Headache and mechanical sensitization of human pericranial muscles after repeated intake of monosodium glutamate (MSG)." J Headache Pain. 2013;14:2. DOI: 10.1186/1129-2377-14-2. PMID 23565943. PMCID PMC3606962.
3. Yang W, Drouin M, Herbert M, et al. "The monosodium glutamate symptom complex: assessment in a double-blind, placebo-controlled, randomized study." Am J Clin Nutr. 1997;66(5):1069–1072. DOI: 10.1016/s0091-6749(97)80008-5. PMID 9215242.

Disclaimer: For information only, not medical advice. This short describes population-level research on MSG and headache, not a diagnosis. If you get headaches after eating, that is worth discussing with your doctor — and if you react to MSG, the main practical step is usually to identify and avoid it in your own diet.