Understanding the Truth: Can MSG Make You Feel Bad the Next Day?

November 10, 2025 •

6 min read

While the FDA classifies MSG as "generally recognized as safe," persistent myths suggest it can cause adverse health effects. A key question that lingers is, can MSG make you feel bad the next day? This article separates fact from fiction, exploring the science behind reported symptoms and the more likely culprits for your post-meal malaise.

Quick Summary

Reports of feeling unwell the day after consuming MSG are common, but scientific evidence shows most potential symptoms, if they occur, manifest within hours and are not severe. Discomfort is more often related to high sodium, fat, and processed ingredients in meals.

Key Points

MSG Is Not Harmful for Most: The FDA and other regulatory bodies confirm that MSG is safe for consumption in standard dietary amounts for the general population.
Symptoms Are Immediate, Not Delayed: Any adverse reactions, known as MSG symptom complex, are typically mild and occur within hours of consumption, not the following day.
Blame High Sodium and Fat: Next-day discomfort like headaches and bloating is more likely caused by the high sodium, calorie, and fat content of many processed meals that also contain MSG.
Context and Dosage Matter: Clinical evidence suggests reactions are most often tied to extremely high, unrealistic doses of MSG consumed on an empty stomach, rather than a normal serving within a meal.
Separating Cause and Effect: The perception that MSG is the culprit can be a psychological 'nocebo' effect, distracting from other, more obvious dietary factors impacting your health.
Track Your Triggers: If you suspect MSG sensitivity, keeping a food diary is the most effective way to identify a pattern, but be aware of other ingredients that could be the real source of your symptoms.
Sensitivity is Rare: A very small percentage of the population reports MSG sensitivity, and controlled studies have not been able to consistently and reproducibly trigger reactions.

The Science Behind the MSG Controversy

Monosodium glutamate (MSG) is the sodium salt of glutamic acid, an amino acid found naturally in many foods like tomatoes, mushrooms, and cheese. It has been used for over a century as a flavor enhancer, adding a savory 'umami' taste to food. The controversy surrounding MSG originated with anecdotal reports in the late 1960s, which led to the popular, though largely unsubstantiated, concept of 'Chinese Restaurant Syndrome'. Today, numerous health organizations, including the US Food and Drug Administration (FDA), classify MSG as 'generally recognized as safe' (GRAS).

How MSG Affects the Body: The Immediate and Short-Term Picture

For the vast majority of people, consuming MSG in typical food amounts has no adverse effects. However, a small subset of the population reports a constellation of temporary symptoms known as MSG symptom complex. These symptoms, which may occur within two hours of consuming MSG, include:

Headaches or a tightening sensation in the head
Facial pressure or flushing
Sweating
Numbness, burning, or tingling in the face, neck, or other areas
Nausea
Drowsiness or fatigue
Chest pain or palpitations

Importantly, these reactions are typically mild, self-limiting, and resolve on their own, usually within a few hours. They are also generally linked to consuming high doses of MSG—3 grams or more—without food, which is far more than the average person consumes in a day. While there have been some anecdotal reports of delayed reactions like angioedema (swelling) persisting for longer periods, conclusive scientific evidence supporting widespread delayed effects is lacking.

The Truth About the "Next Day" Feeling

So, if MSG reactions are typically short-lived, why might you feel bad the day after eating a meal with MSG? The most likely explanation is not the MSG itself, but rather the overall composition of the meal. Foods containing added MSG are often highly processed, high in sodium, and rich in fat.

High Sodium Intake: Many of the most common complaints associated with a 'next day' feeling, such as bloating, thirst, and headaches, are classic signs of excess sodium consumption. A salty meal, like many restaurant dishes, can lead to dehydration and discomfort the following day.
Processed Ingredients: Meals with MSG are frequently part of a larger, more complex matrix of processed ingredients. These can include flavorings, preservatives, and high amounts of sugar or unhealthy fats, all of which can contribute to digestive upset and a general feeling of sluggishness.
Overeating: The 'umami' flavor that MSG enhances can contribute to increased appetite and palatability, potentially leading to overeating. A larger-than-normal portion of a heavy, rich meal can easily cause indigestion and discomfort that lasts well into the next day.

MSG vs. High-Sodium, Processed Foods

It is often difficult for individuals to isolate the effects of MSG from the effects of a typical restaurant or processed meal. The following table compares the typical symptoms and timelines.


Feature	MSG Symptom Complex (In Sensitive Individuals)	High-Sodium / Processed Meal Side Effects
Onset of Symptoms	Typically within 2 hours of consumption.	Can begin during the meal and last for many hours, including the next day.
Common Symptoms	Headache, flushing, sweating, facial pressure, numbness.	Bloating, thirst, dehydration, headache, fatigue, lethargy, digestive issues.
Primary Cause	Potential sensitivity to a high bolus dose of MSG (typically without food).	High intake of sodium, fat, and calories in a single meal.
Resolution	Usually resolves within a few hours.	May persist overnight and into the next morning, particularly feelings of bloating and sluggishness.

What to Do If You Suspect MSG Sensitivity

If you believe you may be sensitive to MSG, the best course of action is to track your diet carefully. Keeping a detailed food diary of what you eat, along with any symptoms you experience and their timing, can help you identify a potential link. However, this can be complicated by the presence of natural glutamate in many foods and the fact that many processed ingredients contain hidden forms of glutamate, such as hydrolyzed vegetable protein, yeast extract, and soy extracts.

For those who notice a consistent pattern, a dietary elimination can be helpful. This involves avoiding all foods with added MSG for a period and then reintroducing them to see if symptoms recur. Working with a healthcare provider or a registered dietitian can provide a more controlled approach. Remember, in most cases, the discomfort is likely caused by the overall dietary habits rather than the MSG alone. It is easy to blame a single, controversial ingredient, when the true culprit is often a combination of factors in a highly palatable, yet unhealthy meal.

Conclusion

In conclusion, the idea that consuming MSG will reliably make you feel bad the next day is a persistent health myth. While a small number of sensitive individuals may experience mild, short-term reactions within hours of eating a very large, unrealistic dose, these symptoms rarely persist until the following day. The feeling of post-meal discomfort or a 'food hangover' is far more often attributable to the high sodium content, excessive fat, and overall processed nature of many dishes that also happen to contain MSG. By focusing on overall dietary patterns and paying attention to total sodium and processed food intake, you are more likely to solve the mystery behind your next-day discomfort. The FDA and other major health bodies continue to affirm the safety of MSG in typical consumption levels. Learn more about MSG safety on the FDA website.

Key Takeaways

Scientific Consensus: Health authorities like the FDA consider MSG safe when consumed at typical dietary levels.
Symptoms are Immediate: Reported symptoms from MSG symptom complex generally occur within two hours and are temporary, not lasting until the next day.
High-Dose Trigger: Adverse reactions are typically associated with unrealistically large doses of pure MSG consumed without food, not with small amounts in meals.
Sodium is the Culprit: The high sodium, fat, and calorie content of processed and restaurant foods containing MSG are the most common cause of next-day bloating, thirst, and headaches.
Nocebo Effect: For some, the belief that MSG is harmful can contribute to perceived symptoms, a phenomenon known as the nocebo effect.
Individual Sensitivity is Rare: Reproducible MSG sensitivity has been difficult to demonstrate in controlled clinical studies.

FAQs

Question: What exactly is MSG symptom complex? Answer: MSG symptom complex is a term for a set of temporary and mild symptoms—such as headaches, flushing, and sweating—that some people report experiencing within a couple of hours of consuming MSG.

Question: How long do MSG symptoms last? Answer: For those who experience symptoms, they are typically mild and short-term, resolving on their own within a few hours. Severe, long-lasting reactions are extremely rare and not consistently linked to MSG in a reproducible manner.

Question: Is MSG sensitivity a real food allergy? Answer: No, MSG sensitivity is not a true food allergy. Allergies involve an immune system reaction, whereas MSG sensitivity is considered a food intolerance.

Question: Can MSG cause a headache the next day? Answer: A headache experienced the next day is highly unlikely to be from MSG. MSG-related headaches, for those sensitive, typically occur shortly after consumption and resolve quickly. Next-day headaches are more often caused by dehydration from high-sodium foods.

Question: Why do people think MSG causes problems? Answer: The perception of harm comes from decades of anecdotal reports, cultural stigma tied to 'Chinese Restaurant Syndrome', and early, flawed studies using excessive doses. Controlled studies have struggled to confirm a link in the general population.

Question: How can I tell if a highly processed meal is making me feel bad, not the MSG? Answer: Try a simple dietary experiment. Compare how you feel after a low-sodium, low-fat meal with natural sources of glutamate (like Parmesan cheese or tomatoes) versus a high-sodium, high-fat processed meal with added MSG. Pay close attention to timing and the specific type of discomfort.

Question: What are some hidden sources of glutamate in food? Answer: Beyond labeled MSG, ingredients like hydrolyzed vegetable protein, autolyzed yeast extract, soy extract, and protein isolates contain free glutamate and can trigger symptoms in highly sensitive individuals, though conclusive evidence is limited.

Frequently Asked Questions

Scientific evidence does not support a causal link between MSG consumption and a next-day headache. Any headaches reported in sensitive individuals usually occur within a couple of hours and are a short-term effect. Next-day headaches and thirst are more often associated with high-sodium meals.

MSG symptom complex refers to a group of mild and temporary symptoms—such as headaches, flushing, sweating, and facial pressure—that a very small percentage of the population may experience shortly after consuming MSG.

To determine the true cause, it is best to examine the meal as a whole. Pay attention to its sodium, fat, and calorie content. Foods with MSG often contain high levels of these, which are more common causes of next-day discomfort. A food diary can help you identify patterns.

No, MSG sensitivity is considered a food intolerance rather than a true allergy. A food allergy involves an immune system response, which does not happen with MSG reactions. This is why reactions are generally milder and resolve on their own.

Yes, it is possible for a small number of people to have a sensitivity to MSG, but controlled studies have failed to consistently prove this link, especially when MSG is consumed with food. Any reactions tend to be mild and temporary.

Common symptoms can include headaches, flushing, sweating, facial pressure or tightness, tingling, and numbness. These are typically short-lived and occur within a few hours.

For most people, no. The reactions observed in some studies occurred with very high doses of MSG (3 grams or more) taken without food. A typical portion of food with added MSG contains significantly less than this amount.

Not necessarily. Many restaurant dishes contain other high-sodium, high-fat ingredients or natural sources of glutamate, such as aged cheeses, that can cause similar or worse symptoms. Focus on overall dietary balance rather than isolating MSG.