I’d never considered taking Theanine WITH coffee. I’ve taken supplements separately.
To mitigate caffeine jitters, and add fat, I use whipping cream in my coffee at home. When at a coffee shop, I use the fattiest cream possible. I only recently found out that you can request heavy cream at Starbucks.
I used to find that overall, most of the supplements sold at Shopper’s Drug Mart were lower quality, but I also haven’t looked in a while. They may have improved, especially since Loblaws carries some better brands and they’re all one company now. I’m in Toronto and have my favourite supplement stores.