This study investigated 11 psychoactive contaminants in wastewater influents at a municipal wastewater treatment plant in Slovakia between 2015 and 2018, based on 44 samples collected under regular conditions and an additional five samples collected during two music festivals in 2018. In addition, 17 progestagens were analyzed only in 2018 during festival days and their corresponding background days. Seasonal variation in normalized mass loads was generally minor, whereas interannual differences were more pronounced, particularly for psychoactive pharmaceuticals, which showed an overall decrease in 2018. Short-term but substantial increases in contaminant loads were observed during the festivals. During the multi-genre music festival, the normalized mass load of 3,4-methylenedioxymethamphetamine increased by more than 110-fold on the second festival day compared to the pre-festival average, while benzoylecgonine increased approximately 17-fold and dienogest by 1.3-fold. During the country/folk music festival, tramadol loads increased approximately twofold. Principal component analysis explained 70.75% of the total variance using the first two components and revealed a clear separation between festival and background samples. Overall, the results demonstrate that music festivals represent episodic pollution events capable of markedly altering wastewater influent composition over short time periods.