Hi, all. I have a 20 amp dedicated circuit with a GFCI installed in my downstairs bathroom, with an non-GFCI outlet (load) terminating into my upstairs bathroom. All 12/2.

Can I run a fixture off the load line in between the two outlets, like a light and switch?

Sorry, but that circuit is dedicated for bathroom outlets only.

Thanks for the quick reply. I guess I'll ask another dumb question:

I found a separate circuit running through the bathroom wall that I can tag to a new light and switch. Can I put the GFCI and light switch into the same two gang box for convenience, or is that a no-no?

Sure that is no problem,it is just the outlet circuit for bathrooms are dedicated because of the large wattage hair appliances now used. Now, if a outlet circuit is just for one bathroom, then the light and fan in only that bathroom can be connected to that one outlet circuit.