Antihistamines can stop working because your allergies might be getting worse or you might have immune system changes due to aging. You also might not be taking the medication as directed. If you take an antihistamine after being exposed to an allergy trigger, it won't work as well.
Antihistamines. There are still many claims that the effects of antihistamines can wane. More often than not, these diminishing effects are related more to the natural course of a person's allergy than to the drug treatment.
The evidence presented does suggest, however, that patients on prolonged antihistamine therapy may develop clinical tolerance. When this is suspected the dose should be increased or the drug discontinued for a short perior (3 to 14 days) before resuming therapy.
Depending on your symptoms, you can take antihistamines: Every day, to help keep daily symptoms under control. Only when you have symptoms. Before being exposed to things that often cause your allergy symptoms, such as a pet or certain plants.
Long term use of some antihistamines may increase your risk of dementia. Diphenhydramine (Benadryl®) blocks the effects of a neurotransmitter called acetylcholine. This neurotransmitter is vital for memory and learning.
Newer antihistamines like Allegra and Claritin are generally safe for daily use. But allergy medications with decongestants, such as Claritin-D or Benadryl-D, could make your allergies worse with long-term use.
Benadryl. Benadryl (diphenhydramine) is the strongest and most effective first-generation antihistamine, says Roberto Garcia-Ibáñez, M.D., a board-certified allergist and immunologist at The Allergi Group in Tampa, Florida. It's often administered in the emergency room to treat an allergic reaction, he adds.
People rarely develop a tolerance to allergy medications. Common medications like Zyrtec, Allegra, Flonase, and Claritin don't usually stop working. It's time to check for new allergies if your nose is still stuffy and you can't stop sneezing after taking your regular allergy medicine.
There are some potential side effects and there are some cases where long-term antihistamine use can worsen urinary retention or narrow angle glaucoma.
Taking too much antihistamine can lead to adverse side effects and a potential antihistamine overdose. Antihistamines are a class of medication that treat allergy symptoms, such as sneezing, runny nose, and itching. As with any medication, taking too much can be harmful.
There can be several reasons for Claritin not working:
You didn't start taking Claritin soon enough. You don't take Claritin every day. You're expecting Claritin to be a decongestant. The antihistamine Claritin contains (loratadine) doesn't work for you as well as other antihistamines would.
In some cases, over the counter allergy meds stop working because your body has built up a resistance to your usual remedy. However, it is far more common for other changes in your life or your body to be the culprit behind the change and your OTC allergy relief not giving you the results you are used to.
"I would strongly recommend instead of taking a second antihistamine, you actually take a different medication like a steroid nasal spray," Sweet said. That's like taking a Claritin to start your day, plus a shot of Flonase in your nose if your symptoms persist. Saline solution is another nasal spray to try.
Cetirizine is unlikely to do you any harm if you take it for a long time. However it's best to take cetirizine only for as long as you need to. If you take it regularly over a long period there's a very small chance of severe itching if you stop treatment suddenly.
Anticholinergic and alpha-adrenergic side effects
Many over-the-counter antihistamines contain a decongestant as well, and therefore if the user experiences palpitations, the medication should be stopped.
“Zyrtec is found to be more potent, or stronger, in laboratory studies, compared with Claritin,” says Dr. Kung. “It also reaches a higher concentration in the skin, which can be more helpful for skin-related allergies. However, Zyrtec has a greater chance of making you sleepy while taking it.”
“The most common side effects you tend to see are fatigue, headaches, and dry mouth,” says Shih. If you're someone for whom the benefits of regular antihistamine use far outweighs the occasional minor side effect, longterm use is safe for most adults and children, he adds.
When antihistamines block histamine, our appetite can increase. This, plus side effects like drowsiness, could lead to weight gain. Your risk of gaining weight from antihistamines may depend on many factors. But a healthy diet, physical activity, and other lifestyle factors can help you manage your risk.
For many people with allergies, symptoms are the worst around 4 a.m. to 6 a.m. Taking an antihistamine at bedtime may help you or your child feel better in the morning during allergy season.
Allergists recommend long-acting, non-sedating antihistamines — ones that won't make you sleepy — for everyday use. Though you may know them by their brand names, the generic versions tackle the same problems: Cetirizine (Zyrtec®, Aller-Tec®, Wall-Zyr®). Fexofenadine (Allegra®, Aller-ease®, Aller-Fex®, Wal-Fex®).
For mild to moderate allergy symptoms, Allegra or Claritin are preferred because they are non sedating and do not make you feel sleepy. For more severe symptoms that can interfere with work, school or daily activities, Xyzal or Zyrtec may be more effective.
The maximum recommended daily dose is 20 mg, do not exceed this dose, unless told to do so by your doctor. The usual dose of ZYRTEC oral solution is 10 mL, once a day. In children over 6 years of age, the daily dose of 10 mg is given as a single or divided dose.
Sandoz issued a voluntary recall of 1,023,430 units of Zyrtec (10 mg) capsules as a result of failed impurities and a specification being reported for impurity at the 21-month stability time point, according to an FDA Enforcement Report.
Tell your doctor or pharmacist if you are taking other products that cause drowsiness such as opioid pain or cough relievers (such as codeine, hydrocodone), alcohol, marijuana (cannabis), drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), muscle relaxants (such as carisoprodol, cyclobenzaprine), or ...
Antihistamines and Decongestants
Clarinex (desloratadine), an oral antihistamine, is only available with a prescription. But many other prescription antihistamines are available in both OTC and prescription forms, often at the same strength. The same goes for decongestants.