A new study from Sweden is making waves in both the scientific community and among environmental advocates, revealing that anxiety medications commonly used by humans can fundamentally alter the behavior of salmon exposed to these drugs. When traces of clobazam, a prescription drug used to treat anxiety, were introduced to farm-raised salmon, the fish began to display markedly bolder behaviors than their untreated peers. While the consequences might initially appear positive—bolder salmon migrated to the sea more quickly—the broader implications point to serious ecological risks (Newser).
Researchers from the Swedish University of Agricultural Sciences, led by biologist Jack Brand, conducted the study by implanting about 280 farmed salmon with either clobazam, the painkiller tramadol, or no drugs at all. The findings were significant: salmon treated with higher levels of clobazam passed through dangerous hydroelectric turbines two to three times faster than drug-free salmon. According to Brand, “any departure from natural behavior is likely to have potential broad and negative consequences for the population.” This boldness, which at first seems advantageous for migration, may ultimately increase exposure to hazards, particularly in environments drastically altered by human infrastructure—such as Thailand’s Chao Phraya River system, where fish routinely navigate through hydropower dams.
The issue doesn’t stop at clobazam or salmon alone. Recent studies warn that various pharmaceutical pollutants, especially antidepressants like fluoxetine (Prozac), are finding their way into waterways globally, including Southeast Asia. Research reported by Monash University revealed that chronic exposure to even low concentrations of antidepressants can change fish behaviors, disrupt reproduction, and alter social dynamics in aquatic populations (Monash University). For example, male guppies exposed to fluoxetine displayed less cautious and more aggressive behavior, undermining group cohesion and potentially impacting their survival (The Guardian).
For Thailand, these new findings hit close to home. The vast expansion of both aquaculture and pharmaceutical use, combined with often inadequate wastewater treatment, means local rivers and lakes may already contain pharmaceutical residues. As a nation proud of its culinary fisheries—from pla pao (grilled fish) at every night market to the iconic tom yum goong—Thailand is deeply invested in the health of its aquatic ecosystems. Any disruption due to pharmaceutical contaminants could have cascading effects on food security and biodiversity.
Key to the Swedish study is the implication that behavioral changes could extend beyond the confines of artificial hydroelectric settings. Olivia Simmons, a Norwegian biologist not involved with the research, notes that “maybe the bolder fish are spending less time trying to decide if they’re going to go through the scary turbines or not,” accelerating migration but possibly increasing the risks once the salmon reach the open sea. In controlled lab settings, fish with altered behavior due to anxiety medications exhibited reduced schooling—becoming less social—which could make them easier targets for predators and less successful at foraging (Newser).
Pharmaceuticals reach freshwater systems mostly through human waste—either from incomplete metabolism in the body or improper disposal of unused medications. Wastewater treatment plants, including those serving Bangkok and secondary cities, are typically not designed to filter out these micropollutants effectively. As a result, reports from both western countries and Asian urban centers have detected common psychiatric drugs in river sediment and water samples (The Guardian, ABC News).
Historically, Thailand’s rivers have played a central role in food production, transportation, and spiritual life. The presence of unseen pharmacological agents represents a modern challenge, potentially altering ancient migratory patterns of native species like the Mekong giant catfish or the endangered pla buk. In addition to drugs intentionally used during aquaculture to control disease, unintentional contamination from public health sources could combine to magnify these ecosystem disruptions.
The Swedish findings also highlight a crucial gap in environmental risk assessment. Regulations for pharmaceuticals have generally focused on direct human safety, not on the environmental fate of drugs after excretion. Yet, aquatic food webs are intricately interconnected: changes in fish behavior can ripple upstream and downstream, disrupting predator-prey relationships, affecting breeding, and undermining population stability over generations (Monash University).
Looking ahead, international experts warn that these behavioral shifts could manifest in increased mortality rates, reduced reproduction, and even local extinctions. A report by Monash University emphasized that “pollutants affected fish over multiple generations,” pointing to the real risk of heritable effects or cumulative ecological damage (Monash University). Since fish are a mainstay of Thai diets and economies, the consequences could spill over into public health and food security.
What can be done? Experts like Dr. Brand advocate for improved wastewater treatment infrastructure—especially technologies designed to remove pharmaceutical residues—alongside better drug disposal practices. Thai policymakers can take inspiration from initiatives in Europe and Australia, where there is increasing regulation of pharmaceuticals at the source, extended producer responsibility programs, and public education campaigns emphasizing not to flush unwanted medicines down the toilet or sink. On an individual basis, Thais can contribute by returning unused medications to pharmacies or taking advantage of community take-back programs—a step rooted in jai dee (ใจดี), the traditional value of kindness and collective responsibility.
For aquaculture operators in Thailand, incorporating regular water quality testing for pharmaceutical residues may soon become as important as checking for bacteria or heavy metals. Fish farmers should also be aware of the potential behavioral and reproductive changes in their stock, which could affect yields and animal welfare.
In the broader context, these findings remind us of the unseen connections between human health and the environment. The very medicines that grant us peace of mind, when mismanaged, may disturb the delicate balance of aquatic life—potentially changing the flavor, abundance, and cultural significance of Thai fish forever.
Practical recommendations for Thai readers include advocating for stronger regulations on wastewater treatment, safely disposing of unused medications, staying informed about food safety issues, and supporting local research into the impacts of pharmaceutical pollution. As this research develops, policymakers, scientists, and the public must work together to ensure the health of Thailand’s waterways and the generations who depend on them.
Sources:
- Newser: Salmon Grow Bolder on Anxiety Drugs
- Monash University: Antidepressant pollution is rewiring fish behaviour and reproduction
- The Guardian: Prozac in waterways is changing how fish behave, research finds
- ABC News: Pollution from antidepressant production is altering fish behavior and reproductive traits