N-Phenylthiourea (Phenylthiocarbamide) is a phenyl ring-containing organothiourea that acts as an EC 1.14.18.1 (tyrosinase) inhibitor, a diphenolase inhibitor, and a non-competitive inhibitor of the PvdP tyrosinase of Pseudomonas, which inhibits melanogenesis, and is able to be used in genetic taste testing.

N-Phenylthiourea acts as a reversible competitive inhibitor of tyrosinase in DOPA oxidation assays (Ki = 0.21 μM), significantly reducing DOPA-chrome formation[1].

In zebrafish embryos, co-treatment with N-Phenylthiourea (100 μM) and HgCl₂ significantly reduced mercury toxicity, with both mortality and hepatic Hg levels decreasing by 60-fold. In contrast, co-treatment with CH₃HgCl increased toxicity, leading to higher mortality and a 2-fold increase in hepatic Hg accumulation. These results indicate that N-Phenylthiourea has opposite modulatory effects on the toxicity of inorganic and organic mercury[2].