What Are the Signs of an Antihistamine Overdose?

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  • Written By: Meshell Powell
  • Edited By: Melissa Wiley
  • Last Modified Date: 17 August 2018
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An antihistamine overdose is rarely fatal, but there can be significant side effects associated with taking too much of this medication. Some of the most common signs of an overdose include extreme drowsiness, inability to concentrate, and blurred vision. Additional symptoms may involve tremors, seizures, or hallucinations. In the most extreme cases, hyperthermia, abnormal heart rates, and kidney damage may occur. Emergency medical attention is required any time that an overdose of antihistamines is suspected.

The early signs of an antihistamine overdose are often an exaggeration of normal side effects of the drug. These symptoms include drowsiness, dizziness, and problems with focus or concentration. A person who has taken too much of this type of medication typically has a difficult time staying awake and may experience confusion or difficulty concentrating. Muscle spasms or tremors may develop, sometimes leading to seizures.

Blurred vision, ringing in the ears, and dry mouth are frequently seen when an antihistamine overdose is present. Difficulty walking or performing normal tasks may occur due to muscle weakness combined with a state of confusion. Some people may begin to experience hallucinations, seeing or hearing things that do not really exist. If the hallucinations cause combative behavior, law enforcement should be called to help transport the patient to the nearest medical facility.


Hyperthermia is a possible complication of an antihistamine overdose. This condition is characterized by a significantly elevated body temperature and is caused by a disruption in the body's ability to regulate temperature. Symptoms of hyperthermia may include reddened skin that feels hot to the touch, an inability to sweat, and low blood pressure. Left untreated, hyperthermia can cause a loss of consciousness or even death.

Arrhythmia is a medical term used to describe abnormalities in the heart rate and is often seen in cases of an antihistamine overdose. Heart palpitations, dizziness, and shortness of breath are common symptoms of this overdose symptom. Prescription medications are usually administered during treatment in an effort to restore normal heart rhythms, although surgery may be needed if a significant amount of heart damage is present.

Kidney damage is one of the most severe potential symptoms of an antihistamine overdose. If treated early enough, this damage may be reversible. Permanent kidney damage may require dialysis, a procedure that drains the blood from the body, filters it through an external machine, and then returns it to the bloodstream. Kidney transplant may be necessary in the most severe cases, and many people die each year waiting for a suitable donor kidney.


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Post 8

Well, when your skin is itchy and painful and red and your pharmacist suggests this, then I'm taking it. I even told him it worked. I have not reacted to this as yet. I use Cetaphil (expensive) since everything just burns my skin, and the only thing I can use is antihistamines, so I'm taking it. If you think that the reaction will affect me later, please advise. Until then, hello from antihistamines!

Post 7

I've been to the hospital a few times after overdosing on it. It makes you quite panicky, especially as you get a fright from every major movement of muscles, such as breathing and swallowing. An OD will give you quite an uncomfortable time. I tend to get a racing heartbeat, which naturally makes you even more nervous, plus thinking you will not be able to breathe any time. I also get a very dry mouth and throat that do not help with that non being able to breathe thing, either. If you go outside on your own on an OD, stay away from the dark and mirrors. I see spiders especially in mirrors, in the dark human shaped shadows running

around and some towards me … it freaks me out and even though I kind of know, it’s not real at this moment. I am not too sure anymore. I do not recommend to OD on it for fun! It will 100 percent give you a bad, bad trip!
Post 4

I had a similar experience as ysmina. I had such bad allergies after a day of golf that I just lost track of what I had taken and how much. That was three days ago and I still don't feel right. I'm light headed and sick to my stomach. I have been going to work but really feel ill.

Post 3

I'm not sure if I overdosed or if my stomach was very sensitive that day, but the last time I took antihistamines, it gave me nausea and vomiting. I haven't taken any since.

Post 2

@ysmina-- I have a friend who has a history of abusing drugs and he also abused antihistamine medications once.

I'm not sure how much he took but when I went to see him, he was extremely tired and couldn't get out of bed. I stayed with him to make sure he was okay and a few hours later he started hallucinating. He started imagining that there were police in the house which was very scary for both him and me.

I somehow convinced him to go to the hospital and he stayed in the ER overnight. He was okay but the doctors told him that what did was very dangerous and his organs could have been damaged. He started seeing a psychologist after that.

Post 1

I read somewhere that a large number of drug overdoses in the US are from antihistamines. I also have allergies and almost everyone I know is allergic to something or the other. Antihistamines are the best medication for allergies and they're so easy to get to because they are sold over-the-counter. This is probably why we use it liberally but we have to be careful.

I once almost overdosed on antihistamines when I was suffering from a very bad sinus allergy. I was so unwell that I didn't keep track of my doses, I kept taking more because I wasn't feeling better. Thankfully, my husband warned me that I had already taken enough of the medication.

I don't know what would have happened if I had overdosed. It might not have been dangerous but I don't ever want to take that risk.

Has anyone else accidentally overdosed on antihistamines? Were you okay afterward?

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