A note on global stability for a heroin epidemic model with distributed delay

By using the direct Lyapunov method and constructing appropriate Lyapunov functional, the global stability for the heroin epidemic model with distributed delay is investigated. It is shown that the disease endemic equilibrium of the system is globally asymptotically stable whenever it exists. This improves the related results presented in [J. Liu, T. Zhang, Global behavior of a heroin epidemic model with distributed delay, Appl. Math. Lett. 24 (2011) 1685–1692].