Diltiazem and
verapamil inhibit CYP3A4, and they can therefore raise the peak levels of
buspirone by 3- to 4-fold, which increases the likelihood of adverse effects.
The US manufacturers suggest adjusting the
buspirone dose according to response, while the UK manufacturers suggest starting with
buspirone 2.5 mg twice daily. Information about other
calcium-channel blockers appears to be lacking, but most do not commonly appear to interact by inhibiting CYP3A4.