A prescription drug DUI in Mississippi occurs when an individual operates a vehicle while impaired by legally prescribed medication to the point that driving ability is substantially affected. Law enforcement may rely on observed impairment, field sobriety test results, and toxicology findings to support arrest and charges. The presence of a lawful prescription does not automatically prevent charges if officers conclude impairment occurred, but medical documentation explaining dosing and timing is relevant to defense. In Tchula, as elsewhere in Holmes County, the factual context matters: when the medication was taken, the dosage, and whether alternative explanations for observed behavior exist. Gathering medical records and pharmacy documentation promptly helps clarify whether lawful medical use, rather than criminal impairment, explains the evidence.