Yes, it is generally safe for an adult to take 2 Benadryl tablets at once. The typical adult dose of Benadryl (diphenhydramine) is 1 to 2 tablets (usually 25-50 mg of diphenhydramine) every 4 to 6 hours, not to exceed 6 doses in 24 hours, with a maximum total dose of 300 mg per day. However, it is recommended to take the lowest dose necessary for the shortest time to control symptoms. Avoid taking two doses at exactly the same time if it is more than recommended, and do not exceed the maximum daily limit to prevent serious side effects.

If unsure or if there are underlying health conditions, it is advised to consult a healthcare provider before taking Benadryl.