In Ancient Greek, nepenthe (νηπενθές) was once a medicine to counter or treat sorrow. It is one of the earliest anti-depressants known as it literally means 'not-sorrow' from ne (νη) 'not' and penthos (πένθος) 'grief', 'sorrow' or 'mourning'.
In Homeros' Odyssey (Bk IV:220-281) we find possibly the earliest surviving references to nepenthe: ...εἰς οἶνον βάλε φάρμακον, ἔνθεν ἔπινον,
νηπενθές τ᾽ ἄχολόν τε, κακῶν ἐπίληθον ἁπάντων ('in the wine she put a drug, for them to drink, the nepenthes, which gives the forgetfulness of all evils'). It is not possible to identify it by comparing it to the effects of other well know substances that were used to 'treat' psychological problems, such as opium, cannabis or kyphi, the incense that was used in Ancient Egypt for religious and medical purposes.
While wine was extensively use to lighten peoples minds and hearts, it was also a vehicle for drugs. The Homeric texts gives us two pieces of the puzzle: [a] nepenthe must have been a plant-based substance, since, as Homer says, it is one of those products grown in the Egyptian fields, and [b] it must have been solid, because it was stated that it was put it into wine rather than poured.
Although deadly nightshade (Atropa belladonna) itself was poisonous, combined with opium it produced a sort of twilight sleep that blurred the memory of pain without loss of consciousness. Whether it also would let you forget sorrow is disputed, but if true it would make it a type of laudanum avant la lettre.
Nepenthe had antidepressant properties, much like the golden root (Rhodiola rosea), which is still extensively used today for its antidepressant effects. Did I just solve an age-old mystery? We shall never know the answer.
 Rossi: Homer and Herodotus to Egyptian medicine in Vesalius - 2010
 Kakridis: Nepenthe in Psychiatriki - 2011
 Amsterdam et al: Rhodiola rosea L. as a putative botanical antidepressant in Phytomedicine - 2016