This study investigates the effects of open trade policies-OTP on economic growth for the Economic Community of West African States during 1980-2017 by applying the method of fixed effect with instrumental variables. Unlike several studies, we move from the univariate to the multivariate regression to show how the coefficient of OTP reacts. The univariate regression supports the positive effect of OTP on growth. However, the multivariate regression indicates that OTP reduces significantly growth. Meanwhile, these findings are robust to various econometric techniques. Furthermore, the paper shows the complementarity relationship between OTP and financial development. The results have important policy implications.