In Mississippi, a prescription drug DUI occurs when a driver operates a vehicle while impaired by a legally prescribed medication that affects driving ability. The focus is on impairment rather than mere presence of a substance in the body. Officers and prosecutors evaluate driving behavior, roadside observations, and chemical tests to determine whether the medication materially impaired the driver. Local courts in Lowndes County consider the totality of the circumstances, including timing of medication use and observable signs of impairment. Because the law emphasizes impairment, having a lawful prescription does not automatically prevent charges. What matters is whether the medication affected safe driving. Each case turns on specific facts such as dosing, timing, and the relationship between testing and actual driving. Early collection of medical documentation and review of toxicology timing are important steps to clarify whether impairment at the time of driving can be shown or reasonably disputed in court.