A compound of formula: ##STR00001## (wherein X, R.sup.1, R.sup.3, R.sup.4, and R.sup.5 are disclosed herein) or a pharmaceutically acceptable salt thereof (a "Thiadiazolylpiperazine Compound"), pharmaceutical compositions comprising a Thiadiazolylpiperazine Compound, and methods for treating or preventing, e.g., pain, depression and anxiety, in a patient comprising administering to a patient in need thereof an effective amount of a Thiadiazolylpiperazine Compound are disclosed.