Humboldt-Universität zu Berlin - Faculty of Language, Literature and Humanities - Galen's Commentary on the Hippocratic Aphorisms

IV.5

ὑπὸ κύνα καὶ πρὸ κυνὸς ἐργώδεες αἱ φαρμακεῖαι.

At the time of the Dogstar or just before it, the use of drugs is troublesome.

The “Dogstar” (Sirius) is the brightest star in the night sky; it was so called because it formed part of the constellation of the Dog (Canis Major). The date of its heliacal rising, in late July – that is, the first day on which it becomes visible in the night sky just before dawn – was associated with the onset of a particularly hot and dry period of the summer, and with the appearance of related pathologies, including mental derangement.

“The use of drugs” (φαρμακεία) refers specifically to the use of purgative drugs. The instruction to avoid them arises from the perception that the body is already “roasted” or “parched” (in our terms, dehydrated) at this season, rendering  further loss of fluids dangerous.