What Is Cyclic Vomiting Syndrome (CVS)?

Cyclic Vomiting Syndrome (CVS) is a chronic functional disorder of unknown cause, characterized by recurrent episodes of severe nausea and vomiting. Episodes may also be accompanied by abdominal pain, headaches or migraine-like symptoms, and profound exhaustion. Between episodes, individuals typically return to their normal state of health.

CVS most often begins in childhood, but it can persist into adulthood or, in some cases, first appear later in life. During an episode, vomiting may occur repeatedly over hours or days, often at very frequent intervals. Episodes tend to follow a similar pattern for each individual and usually resolve spontaneously.

The Four Phases of CVS

CVS is commonly described as progressing through four distinct phases:

1. Inter-episode phase
   A symptom-free period during which the person feels relatively well.

2. Prodromal phase
   The early warning phase, when the person senses that an episode is about to begin.

3. Vomiting (emetic) phase
   Marked by intense and persistent nausea, repeated vomiting, and other acute symptoms.

4. Recovery phase
   Begins as nausea subsides and ends when appetite, oral intake, energy, and overall well-being return to normal.

Historical Background

CVS was first described in medical literature in the early 19th century. Early clinical observations, many of which remain relevant today, helped establish the defining features of the condition. Modern research suggests that CVS is a disorder of the brain–gut axis, involving neuroendocrine pathways in individuals with an underlying susceptibility. Renewed scientific interest in CVS in the late 20th century led to international collaboration and conferences dedicated to the condition.

Who Is Affected?

CVS can begin at any age, but onset most commonly occurs between 3 and 7 years of age. The course of the condition varies widely, lasting from months to many decades. Although CVS has traditionally been considered a pediatric disorder, adult-onset CVS is now recognized as more common than previously believed.

Females are affected slightly more often than males. Many individuals with CVS have a personal or family history of migraine and/or motion sickness, although this is not universal.

General Characteristics of Episodes

Episodes often begin during the night or in the early morning hours. They are characterized by relentless nausea with repeated vomiting or retching. The nausea is typically severe and unrelieved by vomiting, resolving only when the episode ends.

Affected individuals may appear pale, weak, and withdrawn. Additional symptoms can include abdominal pain, headache, low-grade fever, diarrhea, and dizziness. Repeated vomiting may irritate the esophagus and, in some cases, lead to small amounts of bleeding. Without prompt treatment, prolonged vomiting can result in dehydration and electrolyte imbalance, which may become life-threatening.

CVS is distinct from ordinary vomiting illnesses in both intensity and persistence. For many patients, the defining feature is that the vomiting does not stop on its own for prolonged periods.

Typical Symptoms During an Episode

Common symptoms reported during CVS episodes include:

• Severe, continuous nausea
  Often described as overwhelming and unrelieved by vomiting.

• Repeated vomiting and retching
  Vomiting may occur many times per hour, especially early in the episode.

• Marked pallor
  Skin may appear unusually pale.

• Abdominal pain
  Frequently centered around the upper abdomen or navel and sometimes severe.

• Headache or migraine-like pain

• Low-grade fever

• Diarrhea
  Particularly near the onset of an episode.

• Extreme fatigue or altered responsiveness
  Some patients describe a state of confusion and profound exhaustion while remaining conscious and aware.

• Dizziness and weakness

• Excessive salivation or spitting
  Swallowing saliva may worsen nausea.

• Intense thirst
  Even though fluids often provoke further vomiting.

• Dehydration and electrolyte imbalance
  Many patients require intravenous fluids during severe episodes.

• Blood in vomit
  Usually due to irritation or small tears in the esophagus.

• Unusual or protective behaviors
  Such as lying in a fetal position, avoiding light, withdrawing socially, or compulsive drinking of small amounts of fluid.

• Relief with hot baths or showers
  Many patients report temporary symptom relief with prolonged exposure to hot water.

Hot Bathing and Cannabis Use

Prolonged hot bathing or showering has been reported both in CVS and in cannabinoid hyperemesis syndrome (CHS). While cannabis use is associated with increased frequency of hot bathing behaviors, studies have shown that this behavior also occurs in CVS patients who do not use cannabis. Therefore, hot bathing alone should not be considered diagnostic of cannabis-related vomiting.

When to Seek Medical Care for Dehydration

Severe dehydration requires urgent medical attention. Warning signs include:

• extreme thirst

• dark-colored urine

• infrequent urination

• dizziness, faintness, or lethargy

• dry skin

Infants, children, older adults, and people who cannot clearly communicate symptoms are at increased risk. Warning signs in these groups include lack of tears, dry mouth, sunken eyes, reduced urine output, unusual drowsiness or irritability, and fever.

Untreated severe dehydration can lead to serious complications, including organ damage, shock, or coma.

How Often Do Episodes Occur?

The frequency of CVS episodes varies widely between individuals but tends to remain relatively consistent for each person over time. Episodes may occur anywhere from a few times per year to many times per month. On average, individuals experience around a dozen episodes annually, though some experience far more.

Between episodes, people with uncomplicated CVS are typically symptom-free, with a clear “on-off” pattern. About half of patients show a strong, predictable cyclic pattern to their episodes.