Yes, BrdU (Bromodeoxyuridine) is toxic. It is also teratogenic, cytotoxic, and mutagenic. BrdU results in several adverse effects on cells that incorporate it. It increases the length of the cell cycle, alters DNA stability, initiates the formation of teratomas, and triggers cell death. Cells that incorporate BrdU also experience transcriptional, translational, and mitogenic effects. All of these have major consequences on neurogenesis.