Common Blood Pressure Medication Losartan Breaks Down into Potentially Toxic Compoundsโข in Sunlight, New research Finds
XIAMEN, CHINA – A widely prescribedโ medication for managing high blood pressure, losartan, degrades inโ sunlight-exposed water into byproducts exhibiting both high toxicity and resistance too biodegradation, according to a new study published in Frontiers in environmental Science & Engineering.Researchers investigated the environmental fate of losartan โ(LOS) through halogenation and photolysis, revealing concerning transformationโข pathways and potential risks to aquatic ecosystems.
The study, supported by the National Key R&D Program โof China, the Natural Science Foundation of Xiamen, and the National Natural Science Foundation of China, details how losartan โundergoes reactions with chlorine and bromine-common water disinfectants-accelerated by sunlight. These โprocesses don’t simply eliminate the drug; instead,they create a complex mixture of compounds formed throughโ halogen addition to โthe aromatic ring,hydroxylation,and even ring opening. While the initial breakdown appears rapid, some resulting products persist in the environment โฃand pose a threat to aquatic life.
Researchersโ measured apparent โrate constants (kapp) for chlorination and bromination of losartan. Chlorination rates, measured as kapp, HClO (LOS), ranged โขfrom 0.47 to 8.30 L/(molยทs)โค at pH levels between 5.0 and 8.0.Bromination proved significantly faster, with kapp, HBrO (LOS) values ranging from 8.38 ร 103 to 1.55 ร 105 L/(molยทs) over the same pH โขrange. Losartan degradation occurs via direct photolysis, alongside reactions involving carbonate radicals and โขsingletโ oxygen when exposed to sunlight.The research team’s findings underscore the need for further investigation into the long-term ecological consequences of pharmaceuticalโ runoff and โขthe effectiveness of current โฃwater treatment methods in mitigating theโ formation of these potentially harmful degradation products.โ The full study is available at: https://journal.hep.com.cn/fese/EN/10.1007/s11783-025-1968-9.