Nella Clavinger is the titular 18th-century apothecary, a 41-year-old woman who maintains the shop her late mother established for the treatment of women’s maladies. Though she still offers the healing mixtures her mother sold, Nella also sells poison to scorned and abused women for use against the men who have harmed them. She serves as one of Eliza Fanning’s mother figures, though she self-deprecatingly believes herself too tainted by her work to associate with Eliza and thinks she is at constant risk of “spoiling” her.

From the very beginning of the novel, Nella harbors a great deal of guilt over her work, attributing her mysterious physical illness to the toxins she distributes; she claims that “every poison [she dispenses] [brings] a new wave” (14) of physical pain upon her. She feels as though she is doing a disservice to her mother’s memory by violating one of an apothecary’s primary rules (i.e., not dispensing poison), but she does so anyway after the betrayal she suffered at the hands of her ex-lover Frederick. The discovery that Frederick was married, and that he had used a poison to induce an abortion of their child without her knowledge, irreparably scarring her womb, sets Nella down this path.