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Abstract
Fluoxetine, a widely prescribed antidepressant, has been detected at low concentrations (ppt - ppb) in surface water. Mammalian studies indicate that fluoxetine may inhibit the thyroid axis. In larval frogs, increasing levels of thyroid hormones are necessary for metamorphosis to occur, and the presence of fluoxetine in aquatic habitats may have the potential to decrease thyroid hormone levels and delay the completion of metamorphosis. To test this hypothesis, we exposed Xenopus laevis embryos to fluoxetine until the completion of metamorphosis. Metamorphosis was significantly delayed at 50 ppb, a concentration that would not be expected to occur in the environment. Effects at environmentally relevant concentrations included significant reductions in size at metamorphosis, as well as limb malformations. Because decreased survival and reproductive success have been associated with malformations and reduced size at metamorphosis, our findings suggest that the presence of low levels of fluoxetine in aquatic habitats may adversely affect amphibian populations.