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Source: Thailand Medical News  Oct 22, 2019  4 years ago
Global Misuse Of Antihistamines And Dangers Of Long Term Usage
Global Misuse Of Antihistamines And Dangers Of Long Term Usage
Source: Thailand Medical News  Oct 22, 2019  4 years ago
The rate of people developing allergies globally have gone up over the years by as much as 28% and in developed countries like the US, Britain, Australia and Singapore, the rates are even higher. From food allergies, to pollen and dust allergies, individuals often tend to self-prescribe OTC antihistamines even without consulting a doctor. In the US, Australia, Canada and Britain, sales of drugs like Zyrtec and Claritin have sky rocketed in the last two years. (both are non-drowsy versions of antihistamines.)
In countries like Thailand, people with a slight runny nose will quickly go and buy the famous “Ya Khae Pae” or small yellow Chlorpheniramine tablets that is a type of antihistamines that are sold very cheaply. Despite attempts by local regulatory bodies to restrict its sales due to its drowsiness and slightly opioid like properties, it is still found in many Thai pharmacies.
Whats even shocking was a recent discovery that many Thai women and even men would use antihistamines when they are having their bodies waxed or legs shaved as they claim that it reduces redness and skin inflammation!
Many people are unaware that long term usage of antihistamines have been linked to a whole range  of other severe medical conditions as latest studies have shown.

What are Antihistamines

Histamine is a molecule primarily involved in causing the symptoms of immediate allergy by its local action on smooth muscle fibers and on blood vessels. It acts through four types of receptors, H1 to H4. antihistamines act by blocking H1 receptor actions, which are chiefly responsible for allergic reactions. antihistamines reduce symptoms like itching, nasal congestion, tearing up of the eyes, raised red skin rashes, dizziness, nausea and cough.
Antihistamines  are among the most commonly used drugs and are available in many forms. They are available both by prescription and over the counter. Apart from allergies, they are used to treat the common cold, nausea due to motion sickness, vertigo, and to produce sleepiness, relieve tension and anxiety.
Antihistamines  are classified as sedating (first-generation) or non-sedating (second generation). This is based upon their ability to cross the blood-brain barrier at recommended dosages.
Sedating antihistamines can cause many short-term effects such as urinary retention, constipation, dry mouth, increased appetite, and worsen narrow-angle glaucoma via their action on cholinergic receptors. However, most side effects are mild and stop when the drug is no longer used, or the dose is reduced. Tolerance, or lack of clinical effect, is another problem when these are used for more than 4-5 consecutive days.
Non-sedating antihistamines are used in the long-term control of allergy, as in hay fever, eczema, sinusitis, and chronic urticaria.

What Types of Antihistamines Are Available?

Antihistamines come in different forms, including tablets, capsules, liquids, nasal sprays, and eyedrops. Some are only available by prescription. Others you can buy over the counter (OTC) at your local pharmacy.

Prescription antihistamines include:
Azelastine eyedrops (Optivar)
Azelastine nasal sprays (Astelin, Astepro)
Carbinoxamine (Palgic)
Desloratadine (Clarinex)
Emedastine eyedrops (Emadine)
Hydroxyzine (Atarax, Vistaril)
Levocabastine eyedrops (Livostin)
Levocabastine oral (Xyzal)
OTC antihistamines include:
Brompheniramine (Dimetane)
Cetirizine (Zyrtec)
Chlorpheniramine (Chlor-Trimeton)
Clemastine (Tavist)
Diphenhydramine (Benadryl)
Fexofenadine (Allegra)
Loratadine (Alavert, Claritin)
Certain eyedrops treat symptoms of eye allergies including itchy, watery and red eyes. Some medications   combine an antihistamine and a decongestant to ease congestion.

Short term Side Effects of Antihistamines

Older ones tend to cause more side effects, particularly drowsiness.
Newer antihistamines have fewer side effects, so they may be a better choice for some people.
Some of the main side effects of antihistamines include:
Dry mouth
Nausea and vomiting
Restlessness or moodiness (in some children)
Trouble peeing or not being able to pee
Blurred vision
If you take an antihistamines that causes drowsiness, do so before bedtime. Don’t take it during the day before you drive or use machinery.
Read the label before you take an allergy drug. Antihistamines may interact with other medications you are taking.
Talk to your doctor first if you have an enlarged prostate, heart disease, high blood pressure, thyroid problems, kidney or liver disease, a bladder obstruction, or glaucoma. Also check with your doctor if you are pregnant or nursing.

Long term usage of antihistamines have been associated with the following:
Brain Tumors

One medical study has reported a serious long-term effect, a 3.5-fold increase in the risk of gliomas, a common type of brain tumor in patients with long-term antihistamines use for allergic conditions.  

Alzheimer and Dementia

A few studies have linked long term usage of antihistamines as a contributing factor to developing Alzheimer and also Dementia neurodegenerative diseases. Some of the older antihistamines cross the blood brain barrier and can cause memory loss and even cognitive impairment.

Sleep Issues

We all know to avoid taking a Benadryl before getting behind the wheel of the car, and that's because allergy medicines can cause sleep issues. "Truth is, these medications can impact your daily functioning, so if you are new to them, avoid starting them the night before a big work presentation. And if you find they're causing drowsiness, talk to your doctor about non-drowsy options.

High Blood Pressure

Taking decongestants long-term can lead to increased blood pressure and arrythmias. Any allergy medication with a '-D' at the end of it (Allegra-D, Zyrtec-D) contains a decongestant. They can help in the short-term with drying up your nasal passages and sinuses, but usage beyond seven days can lead to spikes in blood pressure.  Once again, it's best to talk to your doctor about your symptoms to help mitigate any potential health concerns while taking allergy medications.

Vocal Cord Dysfunction

An inhaler can help you breathe, but sometimes, it can cause issues with your voice. Some inhaled asthma medications can weaken your vocal cords and cause a hoarse voice, and in some people they can lose their voices almost completely. This is not the case foreveryone, but speak with your doctor if you start to notice hoarseness as a result of using an inhaler.


Oral antihistamines used for severe allergic reactions, eczema, and asthma, and although they help knock out allergy symptoms, they have long-term side effects, including the development of diabetes. If antihistamines have been prescribed to you for allergies, talk to your doctor about the risk factor for diabetes to help prevent further health issues.

Mood Issues

Certain long-term asthma non-steroid but antihistamines based medications can cause some emotional disturbances. In some people, leukotreine modifiers can cause psychological symptoms, such as depression, aggression, irritability, hallucinations and suicidal thinking or behavior. If you begin to develop any of these symptoms, it's important you talk with your primary physician about how to mitigate these side effects.


In addition to increasing your risk of diabetes, long-term antihistamines use can also affect your likelihood of getting osteoporosis. They affect the metabolism of both calcium and vitamin D, so long-term use can actually lead to osteoporosis.

Liver and Kidney Damage

Long term usages of certain antihistamines have been also associated with Liver and sometimes kidney damage.

Immunity Problems

Long term usage of antihistamines have also been associated with lowering the immunity system and sometimes people with underlying diseases such as Herpes, HPV or HIV can make these conditions more severe.
Advice From Thailand Medical News
Always consult a doctor when planning to take antihistamines and as a rule, never be on a drug for too long as its always best to not just treat the symptoms but understand what is  causing it and preventing it or curing that. Long term usage of antihistamines is detrimental to one’s health.


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