Domperidone, sold under the brand name Motilium among others, is a dopamine antagonist medication which is used to treat nausea and vomiting and certain gastrointestinal problems like gastroparesis (delayed gastric emptying). It raises the level of prolactin in the human body. It may be taken by mouth or rectally.

Side effects may include headache, anxiety, dry mouth, abdominal cramps, diarrhea, and elevated prolactin levels. Secondary to increased prolactin levels, breast changes, milk outflow, menstrual irregularities, and hypogonadism can occur. Domperidone may also cause QT prolongation and has rarely been associated with serious cardiac complications such as sudden cardiac death. However, the risks are small and occur more with high doses. Domperidone acts as a peripherally selective antagonist of the dopamine D₂ and D₃ receptors. Due to its low entry into the brain, the side effects of domperidone are different from those of other dopamine receptor antagonists like metoclopramide and it produces little in the way of central nervous system adverse effects. However, domperidone can nonetheless increase prolactin levels as the pituitary gland is outside of the blood–brain barrier.

Domperidone was discovered in 1974 and was introduced for medical use in 1979. It was developed by Janssen Pharmaceutica. Domperidone is available over-the-counter in many countries, for instance in Europe and elsewhere throughout the world. It is not approved for use in the United States. However, it is available in the United States for people with severe and treatment-refractory gastrointestinal motility problems under an expanded access individual-patient investigational new drug application. An analogue of domperidone called deudomperidone is under development for potential use in the United States and other countries.

There is some evidence that domperidone has antiemetic activity. It is recommended by the Canadian Headache Society for treatment of nausea associated with acute migraine.

Gastroparesis is a medical condition characterised by delayed emptying of the stomach when there is no mechanical gastric outlet obstruction. Its cause is most commonly idiopathic, a diabetic complication or a result of abdominal surgery. The condition causes nausea, vomiting, fullness after eating, early satiety (feeling full before the meal is finished), abdominal pain, and bloating. Domperidone can be used to increase the transit of food through the stomach by increasing gastrointestinal peristalsis and hence to treat gastroparesis. It may be useful in idiopathic and diabetic gastroparesis. However, increased rate of gastric emptying induced by drugs like domperidone does not always correlate well with relief of symptoms.

Domperidone is used off-label in some countries to stimulate lactation or enhance breast milk production, but, as of December 2023, it is not approved for that purpose in any country, and is not approved for use in humans in the United States. Domperidone acts as a peripheral dopamine antagonist and is hypothesized to stimulate prolactin secretion, with a 2003 study supporting that hypothesis.

A 2018 meta-analysis of five randomized controlled trials found that domperidone resulted in a moderate increase of in breast milk volume for mothers of preterm infants with insufficient milk supply. The analysis also indicated that domperidone was well tolerated with no significant difference in maternal adverse events compared to placebo. Domperidone has no officially established dosage for increasing milk supply, but most published studies have used 10 mg three times daily for 4 to 10 days (30 mg per day).

The US Food and Drug Administration (FDA) has expressed concerns about serious adverse side effects and concerns about its effectiveness. The FDA identified serious cardiac adverse events associated with domperidone use in lactating individuals, including arrhythmias, cardiac arrest, and sudden death. Additionally, discontinuation or tapering of domperidone has been linked to severe neuropsychiatric adverse events such as agitation, anxiety, and suicidal ideation. Because of these risks, the FDA strongly cautions against the use of domperidone to enhance lactation.