It is sometimes necessary for the contents of medication capsules to be mixed with certain foods and drinks because children are not always able to swallow the capsules. The compatibility and short-term stability (6h) of melatonin capsules mixed in a variety of liquids and foodstuffs (water, orange juice, semi-skimmed milk, strawberry yogurt, and strawberry jam) were analyzed for degradation. Extraction of melatonin from these common administration vehicles and an analytical assay for the drug and its potential degradation products were developed and validated. The results showed good recovery of melatonin from low- and high-strength capsules for all administration vehicles (between 89% minimum and 111% maximum). The drug was found to be stable in the common liquids and foods tested for up to 6 hours at room temperature (no degradation peak); hence it is unlikely to compromise the results of the Use of Melatonin in Children with Neurodevelopmental Disorders and Impaired Sleep trial.