Antihistamines are typically separated into sedating and non-sedating forms, based on their central-nervous-system effects. Non-sedating antihistamines being less likely to cross the blood-brain barrier.
Antihistamines are some of the most commonly used drugs in medicine, and most are available in multiple forms, both by prescription and in over-the-counter products, alone or combined with other medications. Common uses include short-term treatment of symptoms of the common cold, hay fever, motion sickness, nausea, vertigo, cough, rash or hives, itching and anaphylaxis (an acute allergic reaction to an antigen, such as a bee sting). Sedating antihistamines are sometimes also used as mild sleeping aids. Certain antihistamines, even over-the-counter ones, should not be used in the elderly. Check with your doctor or pharmacist before taking them.
Many antihistamines are also available in topical forms, as creams, nasal sprays and eye drops for local use in alleviating allergic symptoms. Non-sedating antihistamines are typically used in extended or long-term treatment of allergic disorders, including hay fever, sinusitis and chronic rash or hives.