Nepenthe has two main meanings:
1. A mythical drug that induces forgetfulness of sorrow and pain: In this sense, an antonym could be remembrance, grief, suffering, or anguish.
2. Anything that brings oblivion or relief from pain: In this sense, an antonym could be awareness, suffering, agony, or pain.
It's important to consider the context in which you are using the word "nepenthe" to choose the most fitting antonym.