H2 Blockers

What are H2 blockers?

H2 blockers are a class (group) of drugs that work on the cells that line the stomach, reducing the production of acid. They include: cimetidine, famotidine, nizatidine and ranitidine, and come in various different brand names.

What conditions are they used to treat?

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

They have also been 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, another class of drugs, called Proton Pump Inhibitors, are now generally preferred for this use.

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.

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 stimulate 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. Also, H2 blockers are more correctly called ‘histamine H2 receptor antagonists’ – but they are commonly just called H2 blockers.

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 do I take H2 blockers?

Your doctor or pharmacist will advise you of the dose needed and how often you should take it. Read the leaflet that comes with your particular brand for further information.

How quickly do H2 blockers work?

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.

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 can and cannot take H2 blockers?

H2 blockers may not be suitable for people with kidney problems or for pregnant or breastfeeding 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.

What about 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 drug consult the leaflet that comes with your medication.

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 COPD (chronic obstructive pulmonary disease).

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

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.