The upset stomach after drinking protein powder may be related to gastrointestinal allergy, indigestion, lactose intolerance and so on, you can take loratadine, mosapride and other treatments. 1. Gastrointestinal allergy: protein powder is an allergen that induces an allergic reaction in the body, leading to stomach discomfort, which can be treated with antihistamines such as loratadine. 2. Indigestion: If your stomach is uncomfortable due to indigestion, you can take a walk to help digestion, or take pro-dynamic drugs such as mosapride to treat it. 3. Lactose intolerance: Patients who are intolerant to lactose may also experience stomach discomfort. It can be treated by supplementing lactase enzyme, or using microbial preparations containing probiotics, such as Bifidobacterium bifidum and Lactobacillus, which can help reduce lactose intolerance. The above drugs are contraindicated in case of allergy and all should be taken as prescribed by the doctor. If the symptoms of stomach discomfort are severe or persist, it is recommended to go to a regular hospital for consultation, to identify the cause of the disease, and then carry out targeted treatment under the guidance of the doctor.