Can drinking coffee at least once a day increase anxiety? Does coffee increase anxiety? What research has been done on this subject?
There's a lot of studies/articles, but when it comes down to it it's just like any other "drug": it affects each person differently. I drink almost a pot a day, and have since I was around 17/18, and have no worsened conditions if I don't consume coffee. Some months I go with only a cup a day, and others its ~3-4 cups - and nothing changes drastically. As with anything else, especially "drugs", moderation is key. 

This is, of course, anecdotal, so...

Brewing Trouble: Coffee-induced anxiety (WebMD)