1. Your medication may not be targeting the right symptoms.
Some patients enter my office frustrated because of the failure of their antihistamine pills (e.g. Claritin (loratadine), Zyrtec (cetirizine) and Allegra (fexofenadine) to relieve symptoms of nasal-sinus congestion.
Antihistamines chiefly dry up the nose and reduce itching and sneezing. Symptoms of stuffy nose and sinus pressure, however, are not usually relieved by antihistamines. Decongestants (such as Sudafed or phenylephrine) target nasal congestion and sinus pressure by constricting blood vessels in the nose.
In other circumstances, patients have expected their nasal drainage and sneezing to go away after taking Sudafed or Mucinex-D (a combination of guaifenesin and pseudoephedrine). Oral decongestants typically do not dry up the nose, reduce sneezing or itching (as antihistamines do).
Over the past 20 years, combinations of antihistamines and decongestants have emerged in the form of Claritin-D, Zyrtec-D, and Allegra-D (and many others over-the-counter products). Many allergy sufferers have benefitted from their impact on almost all hay fever symptoms. Unfortunately, the decongestant component is not well tolerated by some people with other medical problems (for example hypertension, heart ailments, glaucoma, bladder problems, constipation).
2. You had a late start on beginning your allergy medication.
Tree season in the Midwest may begin as early as February if there is a warm spell. Grass season is often underway by May. I instruct my patients with tree pollen allergy to start their antihistamine and prescribed nasal spray by mid March (sooner if there are allergy symptoms prior to this date). Those who are not allergic to trees but who are allergic to grass begin treatment in mid April. The point is to have treatment initiated 1-2 weeks before the pollen or other allergy triggers are in the air.
Taking allergy medication before having any allergy symptoms is a difficult concept for some people and parents of allergy patients. I often spend several minutes explaining how certain allergy meds work.
Imagine a world class boxer being told by his coach to put his arms up to protect his face from a punch, after feeling the first punch. The first punch could knock him out. In the same regard, you shouldn't wait for allergy symptoms to tell you it is time to take your medication. Of course, it may be difficult to figure out when to start allergy meds if you have not had allergy testing. It is essential to know what you are allergic to.
3. You may not be consistent in taking your medication
On a daily basis, I warn patients not to miss doses of their allergy pills and nasal sprays as the season progresses. A few rainy days may reduce pollen and mold counts considerably but this is often followed by a surge of pollen and mold on the first warm and windy day that follows. If you have missed a few doses or days of your allergy meds, you will be more sensitive to the surge in outdoor allergen. Typically an allergy patient jumps back on the medication in desperation, but finds that it isn't as effective as before. "Have I become immune to my allergy medication?" I am often asked.
Most people do not build a tolerance or develop immunity to allergy medication. The antihistamine still blocks histamine in your body at the same level as earlier in the season, but if you didn't take your medication regularly, you may have allowed the intensity of your allergic problem to reach a much higher level than before. See the point? The medication is not doing less for you.
What can you do?
First, try to avoid the above pitfalls. Additionally, if you are on a prescribed nasal med have your nasal spray technique regularly checked by your doctor (another reason allergy treatment may fail to work).
If your allergy problems affect your work or school productivity or causes you to miss sleep, suffer from daytime fatigue, stay indoors or feel constantly sick, see a board certified allergist. Allergy testing may give you a roadmap for better planning on when and how long to take medications. If meds and environmental controls aren't enough, allergy shots may be recommended.