A two-compartment capsule includes a body, a diaphragm between which seals off the body and provides a first compartment to hold a first ingredient, and a cap applied to the body whereby a space between the inner portion of the cap and the diaphragm defines a second compartment for holding a second ingredient. This disclosure also provides certain ranges for the volumes of the first compartment and the second compartment, as well as a volume ratio of the first compartment to the second compartment, lengths of the first and second compartments, and the length of contact between a sidewall of the diaphragm and a sidewall of the body. Furthermore, particular ingredients and formulations for the two-compartment capsule where volume is critical for a therapeutic effect are disclosed.