Q:

Why do antihistamines make you drowsy?

A:

Quick Answer

Dr. Beth Corn on Everyday Health explains that antihistamines make people drowsy because the medication that penetrates the blood barrier treats the allergy and also affects the brain. In other words, the medication works against the histamine, a chemical produced by the central nervous system, as explained by Mayo Clinic. However, regular use of antihistamines makes them less likely to induce drowsiness because of a buildup of tolerance.

Continue Reading
Why do antihistamines make you drowsy?
Credit: Matt Meadows Photolibrary Getty Images

Full Answer

Joseph Castro, a LiveScience Contributor, explains that histamines from the white blood cells and tissue cells seek out and attach themselves to cells that have histamine receptors when the immune system detects a potentially dangerous foreign substance. The histamines have an inflammatory response that dilates the blood vessels, which increases blood flow to the invasion site. This healing process has an effect on the immune system including regulating sleepiness and wakefulness. Castro notes that this disruption in the brain causes drowsiness.

According to WebMD, nighttime cold medicines include antihistamines, but other medications intended to work during the day do not contain antihistamines because of the potential for drowsiness to occur. Medicines such as Advil Cold and Sinus, Benadryl, Chlor-Trimeton, Comtrex Day/Night, Dimetane and Tavist often include drowsiness as a possible side effect.

Learn more about Side Effects

Related Questions

  • Q:

    Why do some probiotics cause diarrhea?

    A:

    Probiotics assist with the digestive process by increasing the amount of good bacteria in the colon, according to Beth Orenstein for Everyday Health. When this occurs, food moves through the gut and the results look like diarrhea as toxins and digested food are excreted, explains the American Gastroenterological Association.

    Full Answer >
    Filed Under:
  • Q:

    What are long term effects from Advil?

    A:

    Long-term effects of using Advil include potential serious problems involving the stomach, intestines and heart or circulation problems, such as heart attack or stroke, notes Everyday Health. Prolonged use can be fatal and may happen without warning, in particular among older adults.

    Full Answer >
    Filed Under:
  • Q:

    How long do Zantac side effects last?

    A:

    The side effects for Zantac, the brand name for ranitidine hydrochloride, may last up to 8 hours, according Everyday Health. Side effect longevity is dependent on the overall health of the individual, notes Drugs.com. Decreased renal function in geriatric patients reduces how quickly the drug is eliminated, which can prolong side effects.

    Full Answer >
    Filed Under:
  • Q:

    What are some drugs that cause alopecia?

    A:

    Drugs that cause alopecia, or hair loss, include blood thinners such as warfarin and heparin, gout medications such as allopurinol and beta blockers such as ateolol and metaprolol that lower blood pressure, explains Everyday Health. Accutane acne treatment, antiseizure drugs, ACE inhibitors, antidepressants and hormone therapy also cause hair loss.

    Full Answer >
    Filed Under:

Explore