"There are several drugs which boost norepinephrine, so why is milnacipran any different?"
Well, I have already tried several NRIs:
atomoxetine (Strattera) - uncomfortable feeling during O, brain fog remained
buproprion - made me feel jittery, brain fog remained
ritalin - gave me energy and focus before quickly building up tolerance, did not stop the brain fog
duloxetine - felt like bad flu, could not drive or work, withdrawal symptoms, too sick to accurately gauge brain fog
venlafaxine - felt like bad flu, could not drive or work, bad withdrawal symptoms, too sick to accurately gauge brain fog
The effects of duloxetine and venlafaxine (both SNRIs) were interesting. They made me feel terrible - there was no way that I could take them every day. But my POIS felt a bit different while I was on both drugs.
I read that duloxetine and venlafaxine don't have a powerful effect on norepinephrine at low doses. There was only a substantial norepinephrine reuptake inhibition effect at high doses.
Venlafaxine has potency at serotonin transporters which is about 30-fold greater than that at norepinephrine transporters while milnacipran has a similar potency at each transporter. Thus, at low doses, venlafaxine acts essentially as a SSRI, with significant noradrenergic activity only occurring at higher doses.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819762/Trying milnacipran, I was surprised to find that a low one-off dose was sufficient to completely stop the POIS brain fog that I have been accustomed to for so many years. I attributed this to the powerful effect that milnacipran has on norepinephrine reuptake inhibition.
Milnacipran also has multiple reports that it cured the brain fog of fibromyalgia sufferers.