My tongue is very swollen. i just took 1 benadryl (diphenhydramine). how long should it take to work? when should i decide to go to the hospital?

Go To An Urgent Care: A very swollen tongue is a sign of a potentially dangerous allergic reaction. Please get evaluated by a physician right away.

Go soon: I wouldn't mess around with a swollen tongue- this can lead to breathing problems quickly. The real question, after the swelling is addressed, is what caused the swelling, so that it doesn't happen again. Good luck!