Hey, I have been taking Lithium for 15 years and never saw all those warnings about caffeine.

But, caffeine may lower lithium serum concentrations by increasing urinary lithium excretion; ie it makes you pee out lithium more.

Personally, I drink 2-3 diet cokes a day. Mostly just make sure that your blood levels are monitored and you will get a feel for it.

PLus caffeine might not make quench your thirst as much as water or other drinks. Watch that you don't start drinking TONS of juice because you might gain weight.