There is no known drug interaction between No-Doze and Benadryl, so they can be safely taken together. That being said, it is probably best that they not be taken together. No-Doze contains caffeine and is typically taken to stay awake while Benadryl is a sedating antihistamine and is often used to treat insomnia.


Benadryl

Benadryl is a first-generation antihistamine that blocks the binding of histamine to receptors in the body. Histamine is a molecule in the body that triggers allergy side effects, like a runny nose, itching, and a rash. Benadryl is typically used to treat allergic reactions, both mild and severe.


Benadryl can also cause drowsiness and sedation which is why it is commonly used as a sleep aid. 


NoDoz

NoDoz is a caffeine supplement a stimulant typically taken to restore mental alertness and reduce fatigue. This can cause an increase in heart rate and blood pressure, as well as make patients more anxious and cause restlessness. It is recommended that patients with anxiety not take this medication as it can cause an anxiety attack.


Since NoDoz contains a similar amount of caffeine as a cup of coffee, patients should limit their intake of other sources to caffeine to ensure they do not experience side effects.


Taking Benadryl With NoDoz

Benadryl should generally not be taken with no NoDoz as the stimulant effect of NoDoz will be greatly diminished. Conversly, taking NoDoz in the evening with Benadryl may cause insomnia.