Histamine is a biologically active substance that potentiates the inflammatory and immune responses of the body, regulates physiological function in the gut, and acts as a neurotransmitter. Drugs that antagonize these effects by blocking or inhibiting histamine receptors (H receptors) are called antihistamines. Antihistamines are divided into two classes (H1 antihistamines and H2 antihistamines), based on the type of H receptor targeted. H1 antihistamines are mostly used to treat allergic reactions and mast cell-mediated disorders. This subtype is further divided into two generations. While the first-generation H1 antihistamines have a central nervous system effect (drowsiness) and are also used as sedatives. The second-generation H1 antihistamines have less drowsy effects and are used primarily as hypoallergenic drugs. H2 antihistamines are indicated primarily for gastric reflux disease because they reduce the production of stomach acid by reversibly blocking the H2 histamine receptors in the parietal cells of the stomach. Use of most H1 and H2 antihistamines is contraindicated during pregnancy and childhood. First-generation H1 antihistamines are specifically contraindicated in angle-closure glaucoma and pyloric stenosis . H1 1st generation medications: Diphenhydramine (Benadryl) for anaphylactic shock, Doxylamine for nighttime sleep, Clemastine for cold and allergy symptoms and Hydroxyzine to treat anxiety, nausea, vomiting, motion sickness, allergies. Long Term Use Effects There is a 3.5-fold increase in the risk of gliomas , a common type of brain tumor in patients with long-term antihistamine use for allergic conditions. Diphenhydramine (e.g., Benadryl®) beside treating allergy and cold symptoms, it also blocks the actions of acetylcholine, a neurotransmitter that is important for brain functions including learning and memory. A study of this class of drug found that increased use is associated with an up to 54% increased risk of dementia. H1 2nd generation non drowsy medications: Loratadine Claritin , Cetirizine Zyrtec , Fexofenadine Allegra Side Effects sedation, headache, urinary retention, dry mouth and eyes, dizziness and tinnitus. Long Term Use Effects Confusion, dizziness, headaches (Cimetidine may lead to erectile dysfunction and gynecomastia (Swollen male breast tissue)). ↓ Renal excretion of creatinine H2 medications lower stomach acid: Ranitidine Zantac , Cimetidine Tagamet , Famotidine Pepcid Long Term Use Effects Without out stomach acid, you are more likely to become B12 and calcium anemic, because they both require stomach acid to be absorbed properly. Stomach acid also kills bacteria, so without it you are first in line for food poisoning. Take away These H1 medications can greatly reduce allergic reactions / symptoms during the allergy “season”. However, they are not meant to be used 24 x 7. I have seen research showing that continued use of the 2nd generation H1 medications can decrease sensitivity to other possible allergens, which I interpret as it keeps shutting down your body's natural defense to everything. In the middle of winter you're sneezing and itching all over, Is that pollen? Could it be a sensitivity to smoke, or holiday potpourri, or the Christmas tree, or maybe even a food sensitivity to something like the wheat in those cookies you just ate! You need to exercise your immune system now and again or it will go away people! Heaven help us if Zyrtec gets recalled, or we have a shortage at the pharmacy. Sneeze occasionally, it’s good for your sinuses, and if you don’t pollen or anything else gets up your nose, and really cause problems. Use this medications when you are really reacting to the pollen, and then stop using it. Come in and let's figure out what's causing your reflux, and fix it. Taking a medication is not "fixing it", and it will only evolve into a worse condition.