Some common antihistamine medications include:

Antihistamines are administered though several types of methods, including:

• Topical cream. Medications in lotion or ointment form that can be spread directly onto the skin where they are absorbed into the body.
  
  
• Tablet. Solid form of medication that is swallowed. The medication dissolves and is absorbed into the bloodstream through the lining of the stomach and intestines.
  
  
• Liquid. Liquid form of medication that is swallowed. The medication is already dissolved and therefore is absorbed more quickly into the bloodstream through the lining of the stomach and intestines.
  
  
• Nasal spray. Sprays that distribute medicine – through the nose – directly to the nasal passages in the form of a fine mist.
  
  
• Eye drop. A sterile solution or medicine that is applied directly to the surface of the eye in the form of liquid drops.

Some medications combine antihistamines with other drugs (e.g., decongestants) to provide relief for a wider range of symptoms.

There are two types of antihistamine receptors and medications may be targeted toward blocking either type. Histamine 1 (H1) receptors are located in many body tissues, including the capillaries (small blood vessels). They are involved with most allergic rhinitis (hay fever) reactions. Medications designed to block these receptors are called H1 blockers and are the most commonly used type of antihistamines.

Histamine 2 (H2) receptors are located in the lining of the stomach. Medications designed to block these receptors are called H2 blockers. H2 blockers were originally developed to treat stomach ulcers, though they have recently been used in combination treatments with H1 blockers to treat hives.

In addition, antihistamines are divided into either nonsedating or sedating medications. Nonsedating antihistamines offer the benefits of antihistamines without making patients drowsy. Although early forms of nonsedating antihistamines were found to be unsafe, newer types (e.g., loratadine and fexofenadine) are considered both safe and effective at providing relief without sedation. The early, unsafe types of antihistamines have all been removed from the market in the United States.