A popular class of flea and tick drugs for pets may be affecting insects in the wild.
A newly published study in Environmental Toxicology and Chemistry suggests that widely used flea and tick treatments for pets may have unintended effects beyond household animals. According to the research, these medications could enter natural environments and pose risks to insects that play critical roles in ecosystems.
The study focuses on isoxazoline antiparasitic drugs, a relatively recent class of treatments prescribed by veterinarians around the world to control fleas and ticks in dogs and cats. Introduced in 2013, these medications quickly gained widespread use because they were the first oral treatments capable of protecting pets from both parasites for a month or longer. After treatment, animals pass the active compounds out of their bodies primarily through feces.
Environmental Concerns and Non-Target Species
Regulatory authorities have already raised concerns about what happens to these substances after use. The European Medicines Agency has warned that veterinary parasiticides may enter soil and water systems, although detailed information about how much is released into the environment is still limited. Scientists are particularly focused on how these chemicals might affect organisms that are not meant to be exposed to them.
Isoxazoline drugs are formulated to kill fleas and ticks by targeting their nervous systems. However, the same biological mechanisms can affect other insects if they come into contact with the compounds after excretion. Research increasingly shows that treated pets can introduce these chemicals into outdoor spaces not only through feces, but also through urine and shed hair.
Dung feeding insects are considered especially vulnerable. Species such as flies, dung beetles, and some butterflies are essential for breaking down waste, enriching soil, and helping control pests. When these insects consume feces from treated dogs or cats, they may ingest active drug residues. Scientists note that disruptions to these insect populations could ripple through food webs and reduce the natural processes that keep ecosystems functioning.
Studying Drug Elimination in Pets
French researchers here studied 20 dogs and 20 cats owned by veterinary students and treated with isoxazoline antiparasitic drugs over a three-month period. The investigators collected feces samples from the pets to determine the potential exposure of dung-feeding insects may have to the toxic chemicals.
This study examined isoxazoline fecal elimination in dogs and cats. The researchers detected two of the four active substances in isoxazoline antiparasitic drugs in pet feces after the end of the recommended treatment period. The environmental risk assessment indicated that dung-feeding insects could be highly exposed to isoxazoline parasiticides due to pet medication, with potentially disastrous consequences for environmental lifecycles.
Reference: “Prolonged fecal elimination of isoxazoline antiparasitic drugs in dogs and cats: is there a risk for nontarget species?” by Philippe J Berny, Bernadette España, Julie Auré and Julia Cado, 14 January 2026, Environmental Toxicology and Chemistry.
DOI: 10.1093/etojnl/vgaf285
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