A couple of times, when I've been too stressed out, a doctor has prescribed me diazepam.

The funny thing about it, is when I take a diazepam tablet, I instantly start to feel better, even though I realise from a pharmacological viewpoint the diazepam could not yet have been absorbed by my stomach and travelled through my blood to reach my brain yet.

Placebo effect happens even for therapies that actually really work.