Many good points here on bipolar and caffeine, but it's not always "black and white", bipolar or not, caffeine can have different to no effects on people, it can interfer with some meds.
It also can affect people in positive ways, it's really an individual's physical makeup that will determine one's reaction to the stuff. I, and many others in the world can actually drink a lot of coffee and feel hardly any stimulation, while others can have just about a spoon of it and they feel wired.
There are times when it will have a stimulant effect for me, and then just the opposite, so for me it's not a "definate" problem.
I guess it's like that old saying goes, about things in moderation . . .
Check with your doc, and rule out if it's interacting with your meds, or if you need any changes in your meds. sometimes dosages are more of a culprit than a simple thing like caffeine.

Make mine with a double-shot of espresso,please!

Take care