A nepenthes (you will note the word is singular) is a drug or potion that brings welcome forgetfulness of bad memories. It appears in Homer’s Odyssey, in which it was the name of the drug that Paris gave to Helen after he had abducted her to make her forget her old home. It’s from classical Greek nepenthes (pharmakon), “anti-sorrow drug”, where the first word is made up from ne–, not, plus penthos, grief. (The second word is the root of English words such as pharmaceutical.)
Expert plantspeople probably know it best as the botanical name for a genus of tropical carnivorous pitcher plants. As the pitcher plants contain liquid in which the captured insects drown, the botanical name would seem appropriate, though in this case any forgetting is terminal.
Some writers have suggested Homer’s potion was opium. This is one old receipe, which should be enough to make anybody forget anything:
Take of tincture of Opium made first with distilled Vinegar, then with spirit of Wine, Saffron extracted in spirit of Wine, of each an ounce, salt of Pearl and Coral, of each half an ounce, tincture of species Diambræ seven drams, Ambergris one dram: bring them into the form of Pills by the gentle heat of a bath.
The Complete Herbal, by Nicholas Culpeper, 1653.
The word has commonly appeared as nepenthe, lacking its final letter:
“Quaff, oh quaff this kind nepenthe and forget this lost Lenore!”
Quoth the raven, “Nevermore.”
The Raven, by Edgar Allan Poe, 1845.
This is a more recent example:
He was scarcely conscious of her now, for this utterly soft end of a hard day was as soporific as the fabled nepenthe and he could feel himself slipping away, as though his fingertips were relaxing from the edge of the cliff of harsh reality in order that he might drop—drop—through the soft clouds of gathering sleep into the slowly swaying ocean of dreams.
The Robots of Dawn, by Isaac Asimov, 1983.
It would make a wonderful name for some spirituous drink and indeed the owner of an Australian winery has called his enterprise Nepenthe.