Chemical defense is a crucial fitness trait in many organisms, yet its physiological regulation in vertebrate animals is poorly understood. Bufadienolides, the main defensive chemicals of common toads (Bufo bufo), are toxic to predators and other natural enemies, and their synthesis is upregulated by several stressors including predation risk, high competitor density, and pollutants. We hypothesized that bufadienolide production may be stimulated either by corticosterone (CORT), the main glucocorticoid hormone of amphibians, or by the same upstream regulators that stimulate CORT. To test these alternatives, we treated toad tadpoles with 125 nM CORT or 110 µM metyrapone (a CORT synthesis inhibitor that stimulates the upstream regulators by negative feedback) for 2 or 6 days, and then measured their total bufadienolide content. We found that CORT release rates were increased strongly by CORT treatment and less strongly by metyrapone treatment regardless of treatment duration, but only the 6-days treatments affected toxin production. CORT treatment significantly decreased bufadienolide content, and metyrapone treatment showed a similar but weaker effect. These findings suggest that bufadienolide synthesis is not stimulated by CORT; rather, it may respond to stressors via some other regulatory compound that is involved in the stress response. Thus, environmental stress in general, and endocrine disrupting chemicals in specific, may interfere with toxin production, which may affect the fitness of toads and their predators and competitors.