The Compendium of Bheḷa 8.1.11

8.1.11

kanīyasikanīys tu tathā prāṇe kanīyasi | viparītaṃ prayuñjāno na rogānvijayiṣyati ||

in the case of the smallest [age], the smallest dose, and likewise when vitality is lowest. / One who administers the reverse will not conquer diseases;