Headache and nausea together usually point to migraine, but the combination can also signal dehydration, low blood sugar, carbon monoxide exposure, infections, or medication side effects. The two symptoms travel together so often because the brain’s pain-processing pathways are directly wired to the nausea center in the brainstem. When one activates, the other frequently follows.
Figuring out what’s behind your symptoms depends on timing, intensity, and what else is going on in your body and environment. Here are the most common explanations and the details that help you tell them apart.
Migraine Is the Most Common Cause
Migraine is the single most likely reason you’re feeling both headache and nausea at the same time. Nausea is so central to migraine that the International Classification of Headache Disorders lists it as one of the core diagnostic features. A headache qualifies as migraine when it comes with nausea and/or vomiting, or with sensitivity to light and sound. You don’t need all of these, just one pairing.
Migraine headaches are typically throbbing, often on one side, and get worse with physical activity. They last anywhere from 4 to 72 hours. The nausea can be mild queasiness or severe enough to cause vomiting, and it often makes eating or drinking feel impossible. Some people also experience an “aura” beforehand: visual disturbances like flashing lights or zigzag lines, or tingling in the face or hands.
There’s also a connection between migraine and your digestive system that goes deeper than just feeling queasy. During a migraine attack, the stomach slows down significantly. This delayed emptying (called gastroparesis) is one reason oral medications sometimes don’t work well mid-attack: the pills sit in your stomach instead of being absorbed. Research published in Frontiers in Neurology found that this sluggish stomach function isn’t limited to active attacks. Many migraine sufferers show signs of delayed gastric emptying even between episodes, suggesting a chronic gut-brain link.
Vestibular Migraine: When Dizziness Joins In
If your headache and nausea come with dizziness, a spinning sensation, or trouble with balance, you may be dealing with vestibular migraine. This variant produces vertigo episodes that range wildly in duration: about 30% of people have episodes lasting minutes, 30% experience hours-long attacks, and another 30% deal with symptoms stretching over several days. A small percentage have attacks lasting only seconds, though these tend to repeat with head movement or visual stimulation.
The vertigo can show up as a false sense that you’re moving, that the room is spinning, or as dizziness triggered by busy visual environments like grocery store aisles or scrolling on your phone. Nausea and motion sickness sensitivity are common companions. Some people get the vertigo without any headache at all, which makes this condition easy to miss.
Dehydration and Low Blood Sugar
Before assuming something serious, consider the basics. Dehydration is one of the most common reasons for a headache-nausea combo, especially if you’ve been sweating, drinking alcohol, or simply haven’t had enough water. When your body loses fluid, blood volume drops, and the brain’s blood vessels respond in ways that trigger pain. The nausea comes from the overall metabolic stress your body is under.
Low blood sugar works similarly. Skipping meals or going too long without eating causes your blood glucose to drop, and the brain, which depends heavily on glucose, protests with a headache. Nausea, shakiness, and lightheadedness often come along for the ride. Eating something and drinking water may resolve both symptoms within 20 to 30 minutes if this is the cause.
Caffeine Withdrawal
If you recently cut back on coffee, tea, or energy drinks, caffeine withdrawal is a strong candidate. Withdrawal headaches can start within 12 hours of your last caffeine intake and typically peak between 20 and 51 hours after stopping. They can persist for up to 9 days. The headache is usually dull, widespread, and often comes with nausea, fatigue, difficulty concentrating, and irritability.
This happens because caffeine narrows blood vessels in the brain. When you stop consuming it, those vessels dilate, increasing blood flow and pressure in ways that cause pain. Even modest daily habits of one to two cups can be enough to trigger withdrawal if you suddenly stop.
Infections and Illness
Viral infections are another frequent cause. A stomach bug (gastroenteritis) produces nausea and vomiting as its primary symptoms, but headache often tags along due to dehydration, inflammation, and fever. The flu, COVID-19, and sinus infections can all produce both symptoms simultaneously.
With sinus infections, the headache tends to concentrate around the forehead, cheeks, or behind the eyes, and worsens when you bend forward. The nausea in these cases often comes from postnasal drip irritating the stomach, combined with the general malaise of fighting an infection. If you also have fever, body aches, or congestion, an infection is the most likely explanation.
Carbon Monoxide Exposure
This one is less common but important to recognize because it can be life-threatening. Carbon monoxide is an odorless, colorless gas produced by gas stoves, furnaces, generators, and car exhaust. According to OSHA data, exposure at 400 parts per million produces frontal headache and nausea within 1 to 2 hours. At higher concentrations, these symptoms hit faster: 1,600 ppm causes headache, nausea, and dizziness within 20 minutes.
The key clue is context. If your symptoms started after using a gas appliance, running a generator, or being in a poorly ventilated space, and especially if other people in the same location feel sick too, get outside immediately and call emergency services. Carbon monoxide poisoning mimics many common illnesses, which is why it’s sometimes called “the great imitator.”
Medication Side Effects
Many common medications list headache and nausea among their side effects. Birth control pills, antibiotics, blood pressure medications, and anti-inflammatories like ibuprofen (especially on an empty stomach) can all trigger both. Overusing pain relievers themselves can paradoxically cause what’s known as a rebound headache, where taking headache medication more than two or three days a week leads to more frequent headaches, often with nausea.
If your symptoms started around the same time as a new medication or a dosage change, that connection is worth noting and discussing with whoever prescribed it.
Electrolyte Imbalances
Your body depends on a careful balance of sodium and other electrolytes to function properly. When sodium drops below its normal range (a condition called hyponatremia), headache, nausea, muscle cramps, and confusion can develop. This can happen from drinking excessive amounts of water without replacing electrolytes, prolonged vomiting or diarrhea, or certain medications that affect fluid balance.
On the other end, when sodium climbs too high (hypernatremia, typically from severe dehydration), nausea, muscle weakness, and restlessness are common. Severe symptoms of low sodium, like seizures or loss of consciousness, generally occur when levels fall significantly below normal, but milder symptoms like headache and nausea can appear with moderate drops.
Increased Pressure Inside the Skull
A less common but serious cause is elevated pressure inside the skull, a condition called idiopathic intracranial hypertension. It most often affects younger women, particularly those who are overweight. The headache can mimic migraine and varies widely in character. Visual symptoms are a hallmark: blurred vision, brief episodes of vision “greying out” (especially with position changes), and sometimes double vision.
The greying-out episodes are usually brief, lasting only seconds, and tend to occur when standing up or bending over. If you’re experiencing headaches with any visual changes, that combination warrants prompt medical evaluation, as untreated cases can lead to permanent vision loss.
Warning Signs That Need Urgent Attention
Most headache-and-nausea episodes resolve on their own or respond to rest, hydration, and basic pain relief. But certain features signal something potentially dangerous. Clinical guidelines use a checklist of red flags to identify headaches that need immediate investigation:
- Thunderclap onset: pain that reaches maximum intensity within seconds to minutes, often described as the “worst headache of your life”
- Neurological changes: confusion, altered consciousness, personality shifts, seizures, weakness on one side, or difficulty speaking
- Fever with neck stiffness: suggests possible meningitis
- New headache pattern after age 50: raises concern for conditions like giant cell arteritis or mass lesions
- Progressive worsening: headaches that have been escalating in frequency or severity over weeks
- Worsening with coughing, straining, or exertion: can indicate structural problems
- Positional component: headaches that dramatically change when lying down versus standing up
Any of these features alongside headache and nausea calls for same-day medical evaluation. A sudden, explosive headache with vomiting is a medical emergency, as it can indicate a ruptured aneurysm or brain bleed that requires immediate treatment.