SSRIs

Fluoxetine, sertraline, paroxetine, citalopram, escitalopram and fluvoxamine block the serotonin transporter, and are selective only in the sense of leaving the other transporters mostly alone. What is not shared is the enzyme profile, and that is where the interactions sit: paroxetine and fluoxetine are strong CYP2D6 inhibitors, so codeine and tramadol — which need that enzyme to become active — are blunted by them; fluvoxamine strongly inhibits CYP1A2; citalopram and escitalopram prolong QT.

The serotonergic risk is the class's own: with an MAOI, with tramadol or with a releaser, serotonin syndrome. The commoner interaction is quieter — an SSRI dulls MDMA's effect, that invites redosing, and the redosing is where the harm is. Stopping is not immediate for all of them either: fluoxetine leaves a long-lived active metabolite behind, and paroxetine's discontinuation is the sharpest.