H2 Blockers

H2 blockers reduce the amount of acid made by your stomach. They are used in conditions where it is helpful to reduce stomach acid. For example, for acid reflux which causes heartburn. Most people who take H2 blockers do not develop any side-effects.

What are H2 blockers?

H2 blockers are a group of medicines that reduce the amount of acid produced by the cells in the lining of the stomach. They are also called 'histamine H2-receptor antagonists' but are commonly called H2 blockers. They include: cimetidine, famotidine, nizatidine and ranitidine, and come in various different brand names.

How do H2 blockers work?

Your stomach normally produces acid to help with the digestion of food and to kill bacteria. This acid is corrosive so your body produces a natural mucus barrier which protects the lining of the stomach from being eroded.

In some people this barrier may have broken down allowing the acid to damage the stomach, causing an ulcer. In others there may be a problem with the muscular band at the top of the stomach (the sphincter) that keeps the stomach tightly closed. This may allow the acid to escape and irritate the oesophagus (gullet). This is called 'acid reflux' which can cause heartburn and/or oesophagitis (inflammation of the gullet).

The letter H in their name stands for histamine. Histamine is a chemical naturally produced by certain cells in the body, including cells in the lining of the stomach, called the enterochromaffin-like cells (ECL cells). Histamine released from ECL cells then stimulates the acid-making cells (parietal cells) in the lining of the stomach to release acid. What H2 blockers do is stop the acid making cells in the stomach lining from responding to histamine. This reduces the amount of acid produced by your stomach.

By decreasing the amount of acid, H2 blockers can help to reduce acid reflux-related symptoms such as heartburn. This can also help to heal ulcers found in the stomach or duodenum.

Note: H2 blockers are a different class of drugs to 'antihistamine drugs' which block H1 receptors in cells that are involved in allergy reactions.

What conditions are they used to treat?

H2 blockers are commonly used:

  • To reduce acid reflux which may cause heartburn or oesophagitis (inflammation of the gullet). These conditions are sometimes called gastro-oesophageal reflux disease (GORD).
  • To treat ulcers in the stomach and duodenum (part of the gut).
  • To help heal ulcers associated with anti-inflammatory medication called non-steroidal anti-inflammatory drugs (NSAIDs).
  • In other conditions where it is helpful to reduce acid in the stomach.

At one time they were used as one part of a treatment to get rid of Helicobacter pylori, a bacterium (germ) found in the stomach, which can cause ulcers. However, proton pump inhibitors are now preferred for this use.

How well or quickly do H2 blockers work?

No one H2 blocker is thought to work any better than another. However, the newer group of medicines mentioned above - proton pump inhibitors - also reduce the amount of acid produced by the stomach. They include omeprazole, lansoprazole, pantoprazole, rabeprazole, and esomeprazole. In general, proton pump inhibitors are used first because they are better than H2 blockers at reducing stomach acid.

Generally, H2 blockers are well absorbed by the body and can provide quick relief of symptoms from some problems. For example, heartburn caused by reflux. However, if you are taking them for other reasons, such as to heal an ulcer, it may take longer for the drugs to have an underlying effect.

What are the possible side-effects?

Most people who take H2 blockers do not have any side-effects. However, side-effects occur in a small number of users. The most common side-effects are: diarrhoea, headache, dizziness, rash and tiredness. For a full list of side-effects and possible interactions associated with your medicine, consult the leaflet that comes with your medication.

Can I buy H2 blockers or do I need a prescription?

You can buy some of these drugs over the counter at pharmacies. They are commonly marketed as drugs for 'relief of heartburn, indigestion, acid indigestion and excess stomach acid' - or similar. However, if you need to use an H2 blocker regularly for more than two weeks, you should consult your doctor.

How long is treatment needed?

This can vary depending on the reason for treating you, so speak to your doctor for advice. In some cases your doctor may prescribe an H2 blocker to use 'as required'. This means you only take it when you need it to relieve your symptoms, rather than every day. In some situations you may be prescribed an H2 blocker to be taken every day.

Who cannot take H2 blockers?

H2 blockers may not be suitable for people with kidney problems or for pregnant or breast-feeding mums. A full list of people who should not take H2 blockers is included with the information leaflet that comes in the drug packet. If you are prescribed or buy an H2 blocker, read this to be sure you are safe to take it.

Note: taking some H2 blockers can affect how well other drugs work. In particular, tell your doctor if you are taking the blood-thinning drug warfarin or a drug for epilepsy called phenytoin (Epanutin®). You should also tell your doctor if you take theophylline, a drug commonly used to treat asthma or chronic obstructive pulmonary disease (COPD).

Other considerations

You should consult your doctor if your symptoms worsen, or if you experience any of the following problems which can indicate a serious gut disorder:

  • Vomiting blood. This may be obviously fresh blood, but altered blood in vomit can look like ground coffee. Doctors call this 'coffee-ground vomit'.
  • Blood in your stools (faeces). This may be obvious blood, or it may just make your stools black.
  • Unintentional weight loss.
  • Difficulty swallowing, including food getting stuck in the gullet.
  • Persistent abdominal pain or persistent vomiting.

If you are taking antacids you should not take them at the same time as you take your other medication, including H2 blockers. This is because antacids can affect how well other medication is absorbed.

How to use the Yellow Card Scheme

If you think you have had a side-effect to one of your medicines, you can report this on the Yellow Card Scheme. You can do this online at the following web address: www.mhra.gov.uk/yellowcard.

The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that your medicines may have caused. If you wish to report a side-effect, you will need to provide basic information about:

  • The side-effect.
  • The name of the medicine which you think caused it.
  • Information about the person who had the side-effect.
  • Your contact details as the reporter of the side-effect.

It is helpful if you have your medication and/or the leaflet that came with it with you while you fill out the report.