Other clinical uses, utilising combined effects: Alcohol detoxification; Acute psychosis with hyperexcitability and aggressiveness; These actions, exerted by different benzodiazepines in slightly varying degrees, confer on the drugs some useful medicinal properties. Zyrtec Overdose: An Overview Zyrtec ® (cetirizine hydrochloride) is a non-prescription medication approved to treat allergies and hives. It is part of a class of medications known as non-sedating antihistamines, which are less likely to cause drowsiness. Drowsiness is one of the most common side effects of Benadryl. Onset of drowsiness usually occurs 20 to 30 minutes after it's ingested. Check with a doctor or pharmacist before administering Benadryl to a child who is on any other medications that may cause drowsiness, as it may intensify the effects. Abusing Benadryl or diphenhydramine can lead to long term mental complications. Explore the adverse effects of Benadryl abuse and the symptoms of withdrawal. Benadryl Overdose – Causes, Effects and Treatment. Benadryl or Diphenhydramine is an antihistamine medicine that cures symptoms of allergies, insomnia, hay fever, and the common cold. Diphenhydramine is an antihistamine mainly used to treat allergies. It is also used for insomnia, symptoms of the common cold, tremor in parkinsonism, and nausea. It is used by mouth, injection into a vein, and injection into a muscle. Maximal effect is typically around two hours after a dose, and effects can last for up to seven hours. Benadryl can cause mild or serious side effects. The following list contains some of the key side effects that may occur while taking Benadryl. What happens if I overdose? Seek emergency medical attention if an overdose is suspected. Symptoms of a Benadryl overdose include extreme sleepiness, confusion, weakness, ringing in the ears, blurred vision, large pupils, dry mouth, flushing, fever, shaking, insomnia, hallucinations, and possibly seizures. When used on a long-term basis (which is often the case when treating allergies), the effectiveness of Benadryl can diminish, so it’s best to rotate through different antihistamines in this case. Benadryl is a brand name for diphenhydramine, an antihistamine. Doctors recommend Benadryl and other diphenhydramine products to treat the symptoms of allergy or hay fever such as a runny nose.