Well, this question can be answered only after investigating how deeply the patient is affected due to allergy. In fact, the allergy medications can last only up to a single day if the allergy is quite mild. The best example for one-day allergic medicine, which is only affected for mildly affected patients, is called generic one-a-day allergic medicine. However, in most of the cases, it has been noticed that the antihistamines such as Zyrtec and Claritin fail to work if used occasionally. In case, if these antihistamines work well depending upon the condition of the allergic patients, it will take no longer than 4 to 5 days to make them get rid of allergy.

No matter what way of treating allergy you have preferred, the medical physicians or doctors will always advice to intake the prescribed products until the allergic conditions are completely eliminated. On the other hand, the number of days of allergy treatment also depends on how big you are. If you are, quite a big person then the treatment days could be more. Benadryl is also advised for those who are mildly suffering from allergy. It will make the patients get rid of allergy within 10 hours.