It is generally not recommended to take Zyrtec (cetirizine) and Benadryl (diphenhydramine) together because both are oral antihistamines and combining them can increase the risk of side effects such as drowsiness, dizziness, and confusion. Taking both together may also lead to antihistamine overdose, which can cause serious symptoms including fast heartbeat, agitation, and poor coordination. However, in some cases, healthcare providers might advise taking both medications on the same day but at different times—such as using Zyrtec during the day and Benadryl at night for additional allergy relief—but this should only be done under medical supervision. Typically, if you have taken Zyrtec, it is advised to wait at least 24 hours before taking Benadryl, as Zyrtec’s effects last about that long, while Benadryl’s effects last 4 to 6 hours. If there is a need to combine allergy medications or if symptoms persist while taking one allergy medication, consulting a healthcare professional is important for guidance and to explore safer alternatives. Summary:

• Avoid taking Zyrtec and Benadryl together unless directed by a doctor.
• Combining them increases risk of side effects and overdose.
• Wait 24 hours after taking Zyrtec before taking Benadryl if needed.
• Consult a healthcare provider for allergy management and medication advice.