Diabetes: Caffeine has been reported to both increase and decrease blood sugar. the downside is that caffeine might be increase the number of low-sugar . So consult the doctor first before drinks for diabetic.
Diarrhea and Irritable bowel syndrome (IBS): Oolong tea contains caffeine. The caffeine in oolong tea, especially when drinks in large amounts , can worsen diarrhea and might worsen symptoms of IBS.