What is the most likely diagnosis and appropriate management for a 29‑year‑old woman who experiences a single morning emesis and uses cannabis each night before bedtime?

Cannabinoid Hyperemesis Syndrome (CHS)

This 29-year-old woman with daily nighttime cannabis use and isolated morning vomiting most likely has early-phase Cannabinoid Hyperemesis Syndrome, and the definitive treatment is complete cannabis cessation combined with amitriptyline 75–100 mg nightly for symptom control. 1, 2

Diagnostic Assessment

The clinical presentation strongly suggests CHS based on the following criteria from the American Gastroenterological Association:

• Cannabis use pattern: Nightly use meets the diagnostic threshold of ≥4 times per week, which is present in 97.4% of CHS cases 2, 3
• Morning-predominant vomiting: The cyclic, morning-only pattern is characteristic of CHS and distinguishes it from other vomiting syndromes 2
• Age and demographics: At 29 years, she matches the typical CHS patient profile (mean age ~30 years) 1

Critical Questions to Confirm Diagnosis

Ask specifically about:

• Hot-water bathing behavior (taking prolonged hot showers or baths for symptom relief)—reported by 71% of CHS patients and serves as a strong bedside diagnostic indicator 1, 2
• Duration of cannabis use (CHS typically requires ≥1 year of regular use, with mean onset after 6.6 years) 1, 2
• Weight loss or decreased appetite, which are core gastrointestinal manifestations 2
• Abdominal pain (present in 85% of cases) 2

Mandatory Exclusions Before Confirming CHS

Perform immediately:

• Urine pregnancy test—pregnancy is a life-threatening differential that must be ruled out in all reproductive-age women with vomiting 2
• Lipase level to exclude pancreatitis 1, 2
• Physical examination for signs of bowel obstruction (distension, absent bowel sounds) or acute abdomen 1, 2

The differential diagnosis after structural exclusions includes cyclic vomiting syndrome (CVS), gastroparesis, rumination syndrome, and functional nausea/vomiting syndrome, but the cannabis use pattern makes CHS most likely 1

Acute Symptom Management

First-line acute treatment:

• Topical capsaicin 0.1% cream applied to the abdomen—provides rapid relief by activating TRPV1 receptors and is readily available 1, 2, 4

Second-line antiemetics if capsaicin fails:

• Haloperidol or olanzapine (antipsychotics)—most efficacious based on case series showing complete symptom relief 1, 5, 4
• Promethazine or ondansetron as alternatives 1
• Benzodiazepines may provide adjunctive benefit 1, 5

Critical pitfall to avoid:

• Never prescribe opioids—they worsen nausea, provide no benefit for CHS, and carry high addiction risk in this population 1, 2

Definitive Long-Term Management

The only curative intervention is complete cannabis cessation:

• Symptoms resolve after 6 months of total abstinence or after a period equivalent to three typical vomiting cycles 1, 2
• No other therapeutic intervention achieves cure without cessation 2

Pharmacologic support during cessation:

• Amitriptyline: Start 25 mg at bedtime, increase by 25 mg weekly to target dose of 75–100 mg nightly (minimal effective dose for preventing recurrence) 1, 2
• Topical capsaicin 0.1% cream can be continued with monitoring for adverse effects 1

Psychiatric Co-Management

Mandatory referral to psychiatry or psychology:

• Anxiety and depression are present in the majority of CHS patients 1, 2
• Co-management is essential for patients with extensive psychiatric comorbidity or lack of response to standard therapies 1
• Recidivism exceeds 40% even after initial treatment success, requiring sustained behavioral counseling 1, 2

Patient Education and Counseling Challenges

Address the paradoxical perception:

• Many patients believe cannabis relieves their symptoms rather than causes them, obscuring the causal relationship 1, 2
• Patients commonly attribute symptoms to diet, alcohol, or stress instead of cannabis use 1, 2
• Explicit education that cannabis cessation is the only definitive cure is essential 4, 3

Pathophysiologic Mechanism (For Patient Understanding)

High-THC cannabis overstimulates CB₁ receptors in the brain's vomiting center (dorsal vagal complex), paradoxically triggering emesis despite cannabis's usual anti-emetic properties at lower doses 2. Peripheral CB₁ activation also impairs gastric motility and acid secretion, contributing to nausea and weight loss 1, 2.

Prognosis

Complete symptom resolution occurs only with sustained cannabis abstinence—this is both the diagnostic confirmation and the definitive treatment 2, 3. Without cessation, symptoms will continue in cycles, leading to repeated emergency department visits, unnecessary testing, and potential complications from severe dehydration 6, 7.