The present invention provides, inter alia, methods for treating or ameliorating the effects of a disease associated with altered serotonin transporter molecule (SERT) activity in a subject in need thereof. The methods include administering to the subject an effective amount of a 5-HT4 agonist or a pharmaceutically acceptable salt thereof. Pharmaceutical compositions and kits for the same are also provided. The present invention additionally provides methods for treating or ameliorating the effects of elevated serotonin transporter molecule activity in the gastrointestinal tract of a subject in need thereof and a gastrointestinal abnormality associated with autism spectrum disorder in a subject in need thereof.
