If H1 antihistamines do not control symptoms of chronic hives within a few weeks, your doctor may try other options. This may include increasing your dose or trying different H1 antihistamines. If this still does not work, your doctor may suggest adding H2 blockers.1-6
H2 blockers are usually used to treat gastrointestinal (GI) problems. However, they may improve symptoms of chronic hives when combined with an H1 antihistamine.1-6
How do H2 blockers work?
H2 blockers are also called H2 antagonists. They work by blocking a protein called the H2 receptor. This prevents a natural chemical called histamine from activating. The activity of histamine is a main cause of symptoms in chronic hives.7,8
H2 blockers may reduce symptoms of chronic hives by narrowing blood vessels. However, the H2 receptor protein is mostly located in the stomach. H2 blockers effectively reduce the production of stomach acid. H2 blockers are most often used to treat GI problems like:3
- Upset stomach (dyspepsia)
- Peptic ulcer disease (PUD)
- Gastroesophageal reflux disease (GERD)
- Heartburn
H2 blockers may slightly improve symptoms of chronic hives. The data on H2 blockers is conflicting. Some studies have shown the benefits of combining H1 antihistamines with H2 blockers. But other studies have shown that H2 blockers are not beneficial.4,5
Some experts do not recommend use of H2 blockers in chronic hives. Other experts suggest trying to add H2 blockers if H1 antihistamines alone do not work. However, you should stop taking H2 blockers if symptoms do not improve within 2 to 4 weeks. Talk to your doctor about what is right for you.1,5
Examples of H2 blockers
H2 blockers are available both over the counter (OTC) and by prescription. Examples of H2 blockers include:1,2,6
- Famotidine (Pepcid®)
- Cimetidine (Tagamet HB®)
- Nizatidine (Axid®)
Other H2 blockers are no longer available. In April 2020, the U.S. FDA removed all prescription and over-the-counter (OTC) ranitidine (Zantac). This was because of an increased risk of cancer. In 2021, a new OTC drug called Zantac 360 became available. But this drug has famotidine as an active ingredient, not ranitidine.1
What are the possible side effects of H2 blockers?
Side effects can vary depending on the specific drug you are taking. Side effects of H2 blockers are usually mild and go away after time. Common side effects of H2 blockers include:2,3
- Constipation
- Diarrhea
- Drowsiness
- Headaches
- Trouble urinating
In rare cases, H2 blockers can cause serious side effects. Call your doctor or go to the hospital if you notice any serious side effects, including:2,3
- Confusion
- Trouble breathing
- Chest tightness
- Irregular heartbeat
- Slurred speech
- Hallucinations
These are not all the possible side effects of H2 blockers. Talk to your doctor about what to expect when taking these drugs. You also should call your doctor if you have any changes that concern you when taking H2 blockers.
Things to know about H2 blockers
Take H2 blockers exactly as your doctor prescribes. All H2 blockers are available as a tablet to take by mouth. Some H2 blockers are also available as capsules, oral solutions, or chewable tablets. Famotidine is available as an intravenous (IV) solution to use in the hospital.3
Talk to your doctor before taking H2 blockers. Certain medical conditions or medicines can increase the risk of side effects. Tell your doctor if you have any medical conditions, especially liver or kidney problems.3
Before beginning treatment for chronic hives, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs.
Despite their potential benefits, there is not yet enough data for all doctors to recommend H2 blockers for everyone with chronic hives.1-6