Why does drinking milk on an empty stomach cause stomach pain?

Drinking milk on an empty stomach may cause abdominal pain due to intestinal spasms or gastrointestinal allergy. It could also be caused by lactose intolerance in the patient.

1. Intestinal Spasms

Abdominal pain after drinking milk on an empty stomach may result from impaired intestinal absorption, which accelerates intestinal motility and leads to intestinal spasms, causing abdominal pain. Treatment usually involves taking oral medications that protect the intestinal mucosa. If the pain is mild, drinking more hot water and keeping the abdomen warm may be sufficient. If diarrhea occurs, oral administration of smectite powder (montmorillonite) can simultaneously help protect the intestinal mucosa.

2. Gastrointestinal Allergy

Milk itself is a food that commonly triggers gastrointestinal allergies, so abdominal pain and diarrhea may occur after drinking it. Drinking milk on an empty stomach may worsen these symptoms. Patients can relieve abdominal pain through massage or warm compresses. It's best to avoid drinking milk on an empty stomach; instead, consume it with easily digestible foods such as steamed buns, bread, or porridge.

3. Lactose Intolerance

Lactose intolerance may stem from congenital deficiency of lactase or from damage to the intestinal mucosa caused by inflammatory bowel disease, medications, surgery, or other acquired factors, leading to temporary or permanent reduction—or even absence—of lactase activity in the small intestine. As a result, lactose in breast milk or cow's milk cannot be fully digested and broken down, causing symptoms such as abdominal pain, diarrhea, nausea, and vomiting after consuming dairy products. Treatment includes taking probiotics (such as bifidobacteria and lactobacilli) or lactase supplements as directed by a physician, maintaining abdominal warmth, and performing gentle abdominal massage to help alleviate symptoms.

In addition, conditions such as gastroenteritis or gastric ulcers may also cause similar symptoms; therefore, early medical evaluation and treatment are recommended. In daily life, pay attention to dietary habits: when choosing milk products, prefer yogurt or lactose-free milk, and avoid drinking milk on an empty stomach. Diarrhea typically gradually resolves after reducing milk intake, and the prognosis is generally good.