What Happens If... You Take Too Many Antihistamines?

Probably best if you just stick to the advice on your anti-histamine packet, to be honest.
Probably best if you just stick to the advice on your anti-histamine packet, to be honest.

Probably best if you just stick to the advice on your anti-histamine packet, to be honest.

It’s that time of year again when allergens hold our senses hostage, and we find ourselves reaching for the antihistamines just to get through the day-to-day.

But, what happens if you accidentally pop too many?

Here’s what you need to know.

What are antihistamines and how do they work?

Histamine is the substance your body makes when you have an allergic reaction after it mistakes something harmless for a threat, according to the NHS.

This substance then causes allergy symptoms by clinging to receptors on certain cells in your body, causing hay fever, hives, conjunctivitis, reactions to insect bites or stings.

An antihistamine is the broad name for a product which helps to suppress your body’s reaction to certain allergens, although sometimes they can be used for motion sickness, nausea, vomiting or insomnia, too.

The product is known for treating symptoms like congestion, runny nose, sneezing, itching, nasal swelling, hives, skin rashes, itchy and watery eyes.

Some can be purchased over the counter, but others are only available on prescription.

There are usually two types of antihistamine – the non-drowsy type and the drowsy type – so it’s worth asking your pharmacist if you’re not sure which type you should take.

As the NHS explains, check with your pharmacist or doctor how you’re supposed to take the medication, including how long you can take it for, when to take it and what other medication you’re on.

Make sure you ask how much to take too, as this can vary according to your age and weight.

Be aware of the side effects as well, and make sure you can differentiate between this and a possible overdose.

What are the side effects?

According to the NHS, these are the most common side effects:

Drowsy antihistamines

  • Sleepiness, reduced coordination, reaction speed and judgement

  • Dry mouth

  • Blurred vision

  • Difficulty urinating

Non-drowsy antihistamines

  • Headache

  • Dry mouth

  • Feeling sick

  • Drowsiness

What are the symptoms of an antihistamine overdose?

These symptoms can be similar to the regular side effects of taking the medication, but those will usually subsidise quite quickly. However, it is still worth talking to a doctor if you have side effects as you might need to alter your dose.

When it comes to differentiating between an overdose and regular side effects, it all comes down to the severity of the symptoms, according to US medical outlet, Healthline.

Overdose with drowsy antihistamines:

  • Increased drowsiness

  • Blurred vision

  • Nausea

  • Vomiting

  • Increasing heart rate

  • Confusion

  • Loss of balance

In extreme cases, drowsy antihistamines can trigger seizures and comas too.

Overdose symptoms with non-drowsy antihistamines:

Non-drowsy antihistamines are typically less toxic and trigger less severe symptoms, but it can still trigger:

  • Dizziness

  • Headache

  • Drowsiness

  • Agitation

Symptoms of an overdose usually become apparent within six hours of taking too much of the medication, and they can start off mild and worsen.

If you notice you’re struggling with a rapid heart rate, tightness in the chest, or convulsions, you need to visit to hospital.

It is possible to die from it, through respiratory distress, cardiac arrest or seizure, based on each person’s tolerance.

According to Healthline, the medication turns toxic when a person ingests three to five times the recommended dose.

How is an overdose treated?

Professionals will administer a patient with activated charcoal in hospital to reverse the effects of poisoning.

This will stop the absorption of toxins and chemicals from the stomach into the body as the toxins cling to the charcoal, and then come out in your poo.

You might also have cardiac and respiratory monitoring.

Healthline adds: “The prognosis depends on the amount of antihistamine ingested and the extent of an overdose, but a full recovery is possible with immediate medical treatment.”

How to make sure you take antihistamines responsibly

Make sure you speak to health professionals before taking the medication, and don’t take two different types at the same time – or exceed the recommended dose.

Don’t double up on doses, and make sure you time your doses to the correct length apart.

Also, be mindful of what other medication you’re taking.

You also shouldn’t give an antihistamine to a child under 2, according to Healthline – and, of course, always read the label.