Question: does benadryl affect serotonin levels?
Answer: Diphenhydramine, a first-generation antihistamine that acts as an inverse agonist on the H1 receptor [3] may also inhibit the reuptake of serotonin. It is known that SSRIs like Fluoxetine are analogs of diphenhydramine [4]. Although weaker, diphenhydramine does retain some activity at the serotonin receptor.