Throwing up everything you eat usually points to one of a handful of causes, ranging from a short-lived stomach bug to a condition that slows your digestion to a near halt. The key to narrowing it down is timing: how soon after eating the vomiting starts, how long it’s been going on, and what other symptoms come with it.
Short-Term Causes: Infections and Food Poisoning
If this started suddenly in the last day or two, an infection is the most likely explanation. Viral gastroenteritis (the “stomach flu”) and bacterial food poisoning account for the vast majority of acute vomiting episodes. The difference between them often comes down to speed. Staph food poisoning, for example, can trigger nausea and vomiting as quickly as 30 minutes after eating contaminated food, especially items like deli meats, pastries, or sandwiches that were handled after cooking. Norovirus, the most common cause of stomach bugs, takes longer: symptoms typically appear 12 to 48 hours after exposure and include watery diarrhea alongside the vomiting.
Salmonella infections can take anywhere from 6 hours to 6 days to show up, often from undercooked poultry, eggs, or unpasteurized juice. E. coli is slower still, with symptoms appearing 3 to 4 days later and frequently involving bloody diarrhea. If you recently ate shellfish, especially raw oysters, both Vibrio bacteria (symptoms within 24 hours) and norovirus are common culprits.
Most of these infections resolve on their own within a few days. The real danger is dehydration, which can set in fast when you’re losing fluids from both ends.
Medications That Cause Persistent Nausea
If you recently started a new medication, that’s worth considering before looking for other causes. GLP-1 receptor agonists, the class of drugs used for diabetes and weight loss (including semaglutide, dulaglutide, and liraglutide), are especially notorious. In a large cross-sectional study, about 23% of patients on these medications reported nausea and vomiting. Dulaglutide and liraglutide had higher rates than semaglutide. Antibiotics, chemotherapy drugs, opioid painkillers, and certain antidepressants can also make it difficult to keep food down. If the vomiting started within days of beginning a new prescription, talk to your prescriber about adjusting the dose or switching.
Gastroparesis: When Your Stomach Empties Too Slowly
Gastroparesis is one of the more common reasons people throw up everything they eat over weeks or months rather than days. The muscles of the stomach don’t contract normally, so food sits there far longer than it should. You might feel full after just a few bites, bloated, and nauseated, then vomit food that you ate hours earlier, sometimes partially undigested.
Diabetes is the leading known cause, but many cases have no identifiable trigger. Gastroparesis is diagnosed with a gastric emptying study: you eat a small meal containing a harmless tracer, and imaging tracks how quickly it leaves your stomach. If more than 60% of the meal remains at 2 hours, or more than 10% is still there at 4 hours, the diagnosis is confirmed. Treatment typically focuses on dietary changes (smaller, more frequent, low-fat, low-fiber meals) and medications that help the stomach contract more effectively.
Gallbladder Problems
If vomiting tends to happen after fatty or greasy meals specifically, your gallbladder may be involved. Gallstones can block the bile duct, causing intense pain in the upper right abdomen that radiates to the back or shoulder blade. This pain, called biliary colic, typically appears within a couple of hours after eating a high-fat meal and improves within a few hours. Nausea and vomiting often accompany the pain. If this pattern sounds familiar, an ultrasound can usually confirm or rule out gallstones quickly.
Bowel Obstruction
A physical blockage in the small intestine is less common but more urgent. The pain is crampy and colicky at first, coming in waves as the bowel tries to push contents past the obstruction. If the blockage worsens, the pain can become constant and severe. Blockages higher up in the intestine cause significant vomiting with less abdominal bloating, while lower blockages produce more distension. One clue: early on, your stomach may make loud, high-pitched gurgling sounds. In more severe cases, those sounds disappear entirely. A bowel obstruction is a medical emergency, particularly if you’ve had prior abdominal surgery, which is the most common risk factor.
Cyclic Vomiting Syndrome
Some people experience intense episodes of vomiting that come and go in a predictable pattern, with stretches of feeling completely fine in between. This is cyclic vomiting syndrome, and it’s more common than most people realize. The diagnostic criteria require at least two acute-onset episodes in six months, each occurring at least a week apart and lasting less than a week, with no vomiting between episodes. Many people with this condition have a personal or family history of migraines, and the episodes can be triggered by stress, sleep deprivation, or menstruation. Between episodes, you feel normal, which is what distinguishes it from most other causes on this list.
Pregnancy and Hyperemesis Gravidarum
If pregnancy is a possibility, it’s worth ruling out even if you haven’t missed a period yet. Morning sickness affects up to 80% of pregnant people, usually starting around week 6. For most, it’s manageable. But a severe form called hyperemesis gravidarum causes relentless vomiting that leads to weight loss of more than 5% of body weight and significant dehydration. This condition requires medical treatment. If you’re pregnant and losing weight, unable to keep any fluids down, or feeling dizzy and weak, don’t wait it out.
Food Reactions Beyond Allergies
Classic food allergies cause symptoms within minutes, but a less well-known reaction called food protein-induced enterocolitis syndrome (FPIES) triggers severe vomiting 1 to 4 hours after eating a trigger food. Common triggers include milk, soy, eggs, grains like oat and rice, and shellfish. Unlike a typical allergic reaction, FPIES doesn’t cause hives or throat swelling. Instead it causes repeated vomiting, pale skin, low energy, and sometimes a drop in body temperature. The delayed timing makes it tricky to identify: you may not connect the vomiting to something you ate hours earlier, especially if the trigger is a food you eat regularly.
How to Rehydrate When You Can’t Keep Anything Down
The most immediate risk from vomiting everything you eat is dehydration and electrolyte loss. The instinct to gulp water or sports drinks after throwing up can actually make things worse. Sports drinks, juice, and soda contain too much sugar relative to sodium, which increases the amount of water your intestines pull into the gut rather than absorb, potentially worsening diarrhea and fluid loss. Plain broth has the opposite problem: too much sodium without enough sugar for your intestines to absorb it efficiently.
Oral rehydration solutions (sold as Pedialyte and similar products) are specifically formulated with equal ratios of glucose and sodium, which is the combination your small intestine absorbs most effectively. The approach that works best is small, frequent sips rather than large gulps. Start with a tablespoon every few minutes. If that stays down for 15 to 20 minutes, gradually increase. Trying to drink a full glass at once when your stomach is already irritated will likely trigger another round of vomiting.
Once you’ve kept clear fluids down for several hours, reintroduce bland, low-fat foods in small portions. If you can’t keep even small sips of fluid down for more than 12 hours, or you notice signs of dehydration like dark urine, dizziness when standing, or a dry mouth with no saliva, that’s the point where you need medical attention rather than home management.