Thanks a lot! :)
To your questions:
The drugs Rachel takes are basically an anti-depressants, but not the usual ones, they're experimental, not available on the market and of course prescription based. Only people with a known case of deep depressions can get these pills and only if a shrink oversees the process regularily.
Regarding the burned apartment: you can hear about it in the news, I know there are some conspiracy theories that Ellie or Rachel might have something to do with it, but that's not the case ;)
To the rest of the questions: No comment :P
They will be answered in future updates and I'm not going to spoiler anything here^^