Methods and compositions useful for enhancing the absorption and/or transport of peptides, peptidomimetics, and other gastrointestinal transport protein substrates through gastrointestinal transport proteins are provided. The methods comprise using hormones such as 5-methoxy-N-acetyltryptamine to increase the transport of the peptides, peptidomimetics, and substrates. The compositions comprise one or more hormones and one or more peptides, peptidomimetics, and other gastrointestinal transport protein substrates.