According to WebMD, there are no drug interactions between Tylenol and Benadryl, so they can be taken at the same time. However, a personal doctor or pharmacist should always be informed, so they can add this information to the medication list.
Tylenol is a brand name for acetaminophen, a type of over-the-counter pain reliever and fever reducer. Benadryl is a brand name for diphenhydramine, an over-the-counter allergy medicine. By themselves, the two medications do not cause any known drug interactions.
Although there are no interactions for them, if a patient is taking other medications in addition to these, these other medicines could result in a drug interaction where there may not have been one previously. For this reason, it is important that a patient's doctor has a correct list of medications being taken at all times.