Do You Know The Common Side Effects of Antihistamines?

Spread the love

Side Effects of Antihistamines

Once allergy season comes around, histamine is released in your body to fight the allergens we are exposed to.  You are fairly sure that you could get relief from an antihistaminebut what are the side effects you need to worry about?  That is what we will address here.

It is important to know at least a little about any medication you take, but knowing the dangerous or serious side effects and drug interactions is extremely important.

Even though antihistamines are considered to be safe medications, as with any drug, there is the potential for side effects.  The issue can be more important if you have high blood pressure, glaucoma, depression, stomach ulcers, urinary problems, or hyperthyroidism.  Be sure to talk with your doctor if you have any of these health problems before using this medication, even the over-the-counter varieties.


Available Antihistamines

There are a variety of these drugs available to treat allergy symptoms.medicine

The most well recognized one on the market is diphenhydramine hydrochloride (Benadryl).  Clemastine, brompheniramine, and chlorpheniramine were some of the other early types that were switched from prescription to over-the-counter.

These older drugs have more side effects compared with the newest types.

The newest are fexofenadine, loratadine (Claritin), and certirizine (Zyrtec).  Prescription antihistamines that are available include:  azelastine, hydroxyzine, desloratadine, cyproheptadine, carbinoxamine, and levocetirizine.

Antihistamines are also found in other formulations.  Ketotifen or the combination of naphazoline and pheniramine are used in over-the-counter eye drops. Emedastine, azelastine, olopatadine, epinastine, and levocabastine are found in prescription eye drops.

Azelastine, olopatadine,and ciclesonide are available as nasal spray formulations, by prescription.

Antihistamines are also available in creams that can be used on allergic rashes or on the itchy skin of eczema.  They include promethazine, hydroxyzine, or alimemazine.


Antihistamine Side Effects To Watch For

The most common potential problems are;

  • Dry mouth, nose, and eyes
  • Along with sleepiness,
  • Slow reaction time, and
  • Difficulty concentrating.
  • Confusion.
  • Difficulty urinating
  • Constipation;
  • Headache;
  • Blurred vision
  • Vomiting and nausea.

You may notice symptoms in  the morning when you take the drug near bedtime.  When taking the older, sedating antihistamines be very careful driving or operating machinery unless you know the sedation effects will not be too much.

Less frequent side effects include;

  • appetite change (increase or decrease – and thus potential weight gain or loss),
  • confusion,
  • constipation or diarrhea, and
  • poor coordination.
  • You may develop headaches or blurry vision, dizziness or difficulties passing urine.


Nasal antihistamines can irritate the lining in your nose.  The dryness they can cause may lead to nose bleeds.  Usually eye drops and skin creams do not cause local problems but if your eyes or skin became irritated you may need to change medications.

It is rare to have side effects such as drowsiness from nasal, eye, or skin cream formulations of antihistamines, but it is not impossible.  Be careful when you start using any form until you know how your body is going to react.


Drug interactions can cause problems toopills

With the older, sedating antihistamines they can easily interact with other sedating medicationsThis means you need to be careful if you also take;

  • strong painkillers such as: morphine,codeine,hydroxycodeine, or dihydrocodeine,
  • use antidepressants, especially tricyclic antidepressants such as amitriptyline,
  • or use benzodiazepines such as diazepam, lorazepam, or temazepam.

Another obvious interaction and potential contraindication would be with sleeping pills.

When taking medications with side effects similar to those of antihistamine you could experience an increase in symptoms.  An example would be a drug that could cause dry mouth and constipation. Taken at the same time as you are taking antihistamines, this could create an extremely dry mouth and significant constipation, unless you are very careful.

Drinking alcohol along with taking antihistamines for allergies can lead to significant sleepiness, so do not combine the two.


Watch Out For Combinationsusing-nasal-spray

When looking for nasal allergy relief, many times you will find combination medications.  It is quite common to find an antihistamine and decongestant (eg Sudafed) together.  They can work very well for your symptoms, but remember that there are decongestant  side effects too.  One very important one is their effects on blood pressure.  If you have hypertension you may not be able to take decongestants, so discuss this with your doctor before allergy season.

The most common decongestant used in these combinations is pseudoephedrine.  A few use phenylephrine.


Natural Antihistamines

There are many foods and supplements that may have positive effects against histamine release.  Caffeine is one of them.  Needless to say, if you drink too much caffeine you could have side effects, which would include jitteriness and insomnia.

The Gale Encyclopedia of Alternative medicine suggests feverfew, grape seed extract, stinging nettle, catnip, ginger root, skullcap, cayenne pepper, black cohosh, and goldenseal as possible natural antihistamines.  Other sources will list other compounds as having such properties.  Anything you take can give you side effects, especially if you take an extra-large dose.  If you are using natural compounds to help with allergies and something starts to happen that is uncomfortable, like diarrhea or a skin rash, then don’t forget to consider the natural supplement as a reason for the problem.


Antihistamine Overdose

Getting too much antihistamine into your system is more common than people think.  It is rarely fatal, but you won’t feel too good for a while.  Parents need to be especially careful with the dose they give to their children.  Always use a dosage spoon rather than a kitchen teaspoon when measuring medications.  Elderly are also at a higher risk of overdose symptoms.

Symptoms include agitation or drowsiness, dilated pupils with blurred vision, low blood pressure, confusion, delirium, diarrhea, dry mouth, flushing of the face, inability to urinate, lack of sweat, fever, motor skill deficits and unsteadiness, nausea, rapid heart rate and abnormal heart rhythms, other nervous system symptoms and rarely seizures. Taking 30 or more pills in less than 24 hours can lead to heart attack, coma, and death.  Even taking 8 to 10 pills in a short amount of time can very serious.

If you believe that you or someone else has taken too much antihistamine it is important to go to the Emergency Room for appropriate care.  Do not try to treat the situation yourself.


Antihistamine Abuse

Delirium experienced from taking antihistamines can include visual and auditory hallucinations.  The person will not be able to tell the difference between the hallucinations and reality and the hallucinations are frequently unpleasant.  This helps limit the number of people interested in using these drugs for recreational use.

The combination use of pentazocine, a pain killer (Talwin), with tripelennamine, an antihistamine (blue tablets), commonly known as “T’s and Blue’s“, reportedly produces a heroin-like effect.  The pills are crushed together and injected to create a reasonable substitute for heroin.  With changes in drug regulation and reformulation of Talwin to include a morphine antagonist, T’s and Blue’s has become a drug of the past.

Types of over-the-counter antihistamines

They include the following:

  • Brompheniramine.
  • Cetirizine.
  • Chlorpheniramine (Chlorpheniramine).
  • Diphenhydramine.
  • Fexofenadine.
  • loratadine

Tips for using antihistamines

Follow these tips if you are taking antihistamines:

  • Take antihistamines that cause drowsiness before bed, and do not take them during the day, especially before driving.
  • Read the label before taking antihistamines for allergies, as they may interact with other medicines you are using.
  • Talk to your doctor first if you have an enlarged prostate, heart disease, high blood pressure, thyroid problems, kidney or liver disease, bladder obstruction or glaucoma.
  • Tell your doctor if you are pregnant or breastfeeding.
  • Avoid drinking alcohol while taking these medications.
  • Avoid grapefruit juice while taking antihistamines; Because it can affect how these medicines work in your body.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.