Likely Effective for. Mental alertness. Drinking oolong tea or other caffeinated beverages throughout the day seems to help maintain alertness and mental performance. Combining caffeine with sugar as an "energy drink" seems to improve mental performance better than either caffeine or sugar alone.

Does oolong tea affect sleep?

Shapiro says oolong tea contains l-theanine, an amino acid that's associated with sleep and relaxation. "This is what is responsible for the relaxing effect oolong tea has," she says. ... Of course, oolong also has caffeine, so you'll feel focused, not sleepy.

Is it bad to drink oolong tea before bed?

It is not recommended to drink oolong tea before bed. While generally containing a lower amount of caffeine than its black tea counterpart, there is still enough caffeine in a cup of oolong to possibly disrupt your sleep cycle.