My girlfriend is on 60mg of cymbalta (duloxetine which is a SNRI) and 5mg of escitalopram (SSRI) would it be safe for her to take 60-100mg of DXM or is this playing with fire (serotonin syndrome)?
The clear answer is no, it's very dangerous to mix DXM with any SSRI or SNRI. You're risking a serotonin syndrom which is potentially lethal. So don't do it!