I’m a huge fan of Yerba mate, and my psychiatrist fully endorses it as a good way to self-medicate in lieu of prescribed stimulants (I lapse every so often as a result of supply issues, or remembering to fill my prescription issues), or just supplement.
Yerba mate has a high caffeine content compared to black and green teas, but for whatever reason, delivers a really smooth caffeine ride with no jitters or stomach problems (which I get from black tea and usually green tea if I’m taking my meds or haven’t eaten). It’s very nice.
Just make sure you get the actual tea (preferably loose leaf) to make yourself (hot or iced) and not the bottled stuff with lots of added sugar. Also, if you don’t like the grassy taste of Yerba mate, you can go to a good tea shop and get it blended with other things like rosehips.