This is known as a drug tolerance.
This can happen after months and years of use.
People who have chronicallergy symptomsare more likely to find that their allergy medicine stops working at some point.
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Others may think they have become drug-resistant, as is possible withantibioticsthat no longer work because bacteria has mutated.
Neither of these explanations is correct.
(This can also occur if you take a lower dose for too long.)
Is Tolerance the Same as Dependence or Addiction?
With certain drugs (particularly psychoactive drugs), tolerance is associated with dependence or addiction.
If You’re Tolerant of One Allergy Medicine Are You Tolerant to All?
For example, the risk of tolerance can be high with beta-agonists.
Nasal decongestant sprays can also cause dynamic tolerance.
Frequent, repeated use can rapidly desensitize the mucosal tissues to the drugs' vessel-shrinking (vasoconstrictive) effects.
Antihistamines
Researchers are not sure why antihistamines stop working.
Most evidence shows that drug tolerance does not happen no matter how long or aggressively the medications are used.
There are still many claims that the effects of antihistamines can wane.
They can help figure out why this may be the case and recommend what to do next.
National Cancer Institute.Definition of drug tolerance.
Merck Manual.Tolerance and resistance to drugs.
Critical review of the literature by a medical panel.European Annals of Otorhinolaryngology, Head and Neck Diseases.
2013;2014(6).
2017;7(1).
doi:10.1186/s13601-017-0141-3
American College of Allergy, Asthma, & Immunology.Runny nose, stuffy nose, sneezing.
