Surveillance of Phenibut in Wastewater During a Brazilian Carnival

Phenibut is a new psychoactive substance (NPS) first synthesized in Russia in 1963 as a derivative of gamma-aminobutyric acid. Originally developed for therapeutic use, it has gained popularity for nonmedical purposes, including recreational and cognitive enhancement. In Brazil, phenibut is uncontrolled and easily purchased online. This study used wastewater-based epidemiology (WBE) to investigate phenibut use patterns in two northeastern Brazilian cities. Composite daily wastewater samples were collected from two treatment plants (WWTPs), Recife (WWTP_A) and Olinda (WWTP_B), during two periods in 2023: Carnival and a reference week. Samples underwent solid-phase extraction (SPE) and analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Phenibut concentrations were converted to population-normalized mass loads (PNMLs, mg/day/1000 inhabitants). The highest phenibut levels and PNMLs (up to 4.06 mg/day/1000 inhabitants) occurred during Carnival at WWTP_A, located in a major tourist area, suggesting recreational use. During the reference week, PNMLs ranged from detection limits to 2.29 mg/day/1000 inhabitants on weekdays, indicating possible functional or cognitive enhancement use. These findings reveal two distinct use patterns: recreational peaks during Carnival weekends and possible functional use on weekdays outside festive periods. This is the first evidence of phenibut detection in Brazilian wastewater and its temporal use patterns. The results highlight WBE's value in monitoring NPS trends and suggest recreational use predominates during large events. This underscores the need for public health attention and regulatory monitoring of uncontrolled substances with abuse potential.