Do you sometimes think you are getting forgetful? Antihistamines (first-generation) may be contributing to your memory loss.

First-generation antihistamines treat allergies by blocking the action of histamine, a substance produced by your body in response to an allergen, causing your allergic symptoms. They are available over the counter and may cause drowsiness.

First-generation antihistamines generally cause more side effects because they can penetrate the brain tissue. Second-generation drugs have fewer side effects because they usually cannot enter the central nervous system.

Examples of first-generation antihistamines include: Brompheniramine (Dimetane), carbinoxamine (Clistin), chlorpheniramine (Chlor-Trimeton), clemastine (Tavist), diphenhydramine (Benadryl) and hydroxyzine (Vistaril).

How do first-generation drugs cause memory loss?

These medications (prescription and over-the-counter) inhibit the action of acetylcholine, a chemical messenger that mediates a wide range of functions in the body. In the brain, they inhibit activity in the memory and learning centers, which can lead to memory loss.

What are the alternatives?

Newer-generation antihistamines such as loratadine (Claritin and Alavert)) and cetirizine (Zyrtec) do not present the same risks to memory and cognition.

Exampes of other second-generation antihistamines include: Astelin(azelastine), Clarinex (desloratadine), Allegra (fexofenadine), Xyzal(levocetirizine) and Patanase (olopatadine).

Many other commonly prescribed drugs also can cause memory loss. Antihistamines rank in the top ten. The other top nine include:

1. Antianxiety drugs (Benzodiazepines)

2. Cholesterol-lowering drugs (Statins)

3. Antiseizure drugs

4. Antidepressant drugs (Tricyclic antidepressants)

5. Narcotic painkillers

6. Parkinson's drugs (Dopamine agonists)

7. Hypertension drugs (Beta-blockers)

8. Sleeping aids (Nonbenzodiazepine sedative-hypnotics)

9. Incontinence drugs (Anticholinergics)