About 54 percent of the American population tests positive for an allergy, according to the American Academy of Allergy, Asthma and Immunology. Multiple approaches may be taken to treating and preventing allergies such as home remedies, prescribed medications and over-the-counter drugs. For most people, using an OTC oral allergy medication helps reduce and prevent symptoms, according to MayoClinic.com.
First-Generation Antihistamines
Most oral antihistamines are available over the counter without a doctor's prescription. Antihistamines are categorized in two separate groups, according to FamilyDoctor.org. First-generation antihistamines are older drugs and noted for their strength and the side effect of marked drowsiness. These strong effects occur because these drugs cross the brain-blood barrier, which is why they are also used to treat motion sickness. The most common first-generation antihistamines are diphenhydramine, doxylamine and brompheniramine. Patients take these drugs every four to six hours as needed, according to FamilyDoctor.org.
Second-Generation Antihistamines
Second-generation antihistamines are newer drugs and come in oral 24-hour doses, according to FamilyDoctor.org. Second-generation drugs do not cause drowsiness in most healthy adults, because they do not cross the brain-blood barrier. Two second-generation antihistamines are available on the market: cetirizine, or Zyrtec; and loratadine, or Claritin. Drugs.com says that cetirizine should not be taken if a person is currently taking a sedative drug and may cause weakness, confusion, lack of mental clarity and problems with vision. Loratadine should not be given to children younger than the age of six without a doctor's recommendation, according to Drugs.com. Overdosing on either second-generation antihistamine can cause significant drowsiness. First-generation and second-generation antihistamine drugs should not be combined.
Decongestants
Oral decongestants are used to treat allergies that affect the sinus cavity. If a person has symptoms of hay fever, such as runny nose, nasal congestion, and sinus headaches, she can use a decongestant to treat the symptoms, according to the American Academy of Otolaryngology. Sinus membranes can easily swell, leading to severe head congestion. Decongestants work by restricting blood flow, causing the membranes to shrink back to normal size. Common side effects of using decongestants are excitability, nervousness, sleeplessness and being jittery, according to the American Academy of Otolaryngology. Decongestants are not recommended for people who suffer from heart disease or high blood pressure.
