Ghost Eaters by Clay McLeod Chapman

Erin hasn’t been able to set a single boundary with her charismatic but reckless college ex-boyfriend, Silas. When he asks her to bail him out of rehab–again–she knows she needs to cut him off. But days after he gets out, Silas turns up dead of an overdose in their hometown of Richmond, Virginia, and Erin’s world falls apart.

Then a friend tells her about Ghost, a new drug that allows users to see the dead. Wanna get haunted? he asks. Grieving and desperate for closure with Silas, Erin agrees to a pill-popping “séance.” But the drug has unfathomable side effects–and once you take it, you can never go back.