For years Colombia has been the world's largest coca producer. Its public management of crops for illicit use has swung between eradication, substitution, and, recently legalization. Forced eradication has been shown to be ineffective, and legalization is an incipient option, so the Peace Agreement puts forward substitution as the path to follow. Yet, what kind of substitution does it suggest? This article analyzes voluntary substitution projects in Peasant Reserve Zones. While some projects have evolved locally due in part to strong peasant associations, they have not gained traction nationally. In general, the difficulties inherent in any business play a role, but there are also structural limitations such as continued fumigations, obligations of prior eradication, the costs of production and transportation due to the lack of infrastructure and public services, and the issue of land rights, which limits peasants' access to the formal funding established by the Peace Agreement.