H2 receptor blockers (or H2 blockers) are a class of medication prescribed to reduce stomach acid production. They’re commonly used to treat acid reflux and gastro-oesophageal reflux disease (GERD). Though not as strong as proton pump inhibitors (PPIs), they’re a popular medication with few side effects. 

These medications can make a big difference for people with recurring heartburn or indigestion, relieving discomfort and helping the stomach settle so it can recover. 

What are H2 Blockers? 

H2 receptor blockers target the histamine-2 receptors located in the stomach. Doing so suppresses the production of stomach acid, preventing damage from acid reflux. 

Too much stomach acid can cause heartburn and irritation of the food pipe (oesophagus) and throat if reflux occurs. If left untreated, it can even lead to peptic ulcer disease in the stomach. 

H2 blockers are often prescribed either as a first-line treatment for acid reflux or as an alternative if PPIs aren’t well-tolerated. Like some PPIs, H2 blockers are available as an over-the-counter (OTC) medicine in the UK. 

Types of H2 Blockers 

Common types of H2 blockers include: 

• Ranitidine (Zantac) – now withdrawn in many countries 

• Famotidine (Pepcid) 

• Nizatidine (Axid) 

• Cimetidine (Tagamet) 

These H2 blockers can have slightly different side effects depending on the person , but they broadly act in the same way. 

How H2 Blockers Work 

Most bodily processes occur because a chemical compound activates a receptor. For example, histamine receptors on the surface of the stomach will release acid if activated. H2 blockers target these receptors. Once bound, they prevent other compounds from binding, thereby lowering stomach acid production.  

Reducing acid levels gives your stomach and upper gastrointestinal (GI) tract time to recover. If you’ve developed a peptic ulcer, this can heal, while any inflammation further up the GI tract can be treated.  

Thanks to being relatively safe long-term, H2 blockers may also serve as a long-term treatment option for excess stomach acid. However, with continued use over time, they do start to lose their ability to reduce stomach acid levels. 

When are H2 Blockers Prescribed? 

H2 blockers have a primary function: to reduce stomach acid production. But they’re not confined to a single condition. H2 blockers are commonly used for: 

• Heartburn. If you’ve got frequent acid reflux or GERD, H2 blockers prevent attacks by reducing acid levels. 

• Healing stomach ulcers. Lowering acid levels gives your gut a chance to heal. 

• Long-term treatment for medical conditions. Rare conditions like Zollinger-Ellison syndrome cause permanent overproduction of stomach acid.  

• Managing acid reflux caused by other medications. Certain medications cause acid reflux. H2 blockers may be prescribed alongside to relieve this adverse reaction.  

How Long Does It Take for H2 Blockers to Work? 

H2 blockers are highly effective at reducing acid production. You can expect to notice relief within 4 to 10 hours.  

H2 blockers are designed to provide long-term relief from acid reflux. They will not provide instant relief during an acid attack. 

If you’re currently experiencing acid reflux, try an antacid like Gaviscon. This will neutralise the acid, preventing further heartburn.  

Side Effects of H2 Blockers 

H2 blockers are extremely well-tolerated. There’s a reason they’re an OTC medication. That being said, some people do experience mild side effects. 

Common side effects of H2 blockers include: 

• Headache 

• Dizziness 

• Diarrhoea 

• Constipation 

• Fatigue 

• Muscle or joint pain 

• Mild rash 

Less common but more serious side effects (seek medical advice if they occur): 

• Confusion (more likely in older adults or those already very unwell) 

• Irregular heartbeat 

• Liver function changes 

• Blood disorders (rare, e.g., low platelets or white cells) 

If you experience any severe side effects, immediately speak to your doctor. You may need to change medications or find an alternative treatment.  

Comparing H2 Blockers to Proton Pump Inhibitors (PPIs) 

PPIs are an alternative to H2 blockers. Both medications reduce stomach acid production, treating conditions like GERD and peptic ulcer disease. Common examples of PPIs include esomeprazole (Nexium) and omeprazole (Prilosec).  

While both medications are effective, H2 blockers are usually prescribed as an evening dose or if you experience symptoms sporadically. Meanwhile, PPIs are often prescribed to those with more extreme or constant symptoms. H2 blockers and PPIs are also sometimes prescribed alongside one another, with a dose of PPI taken in the morning and a dose of H2 blocker taken at night.  

Can I Buy H2 Blockers or Do I Need a Prescription? 

In the UK, you can buy H2 blockers OTC. That means you can buy them from your local pharmacist without visiting your doctor or a prescription. H2 blockers can provide long-term relief from acid reflux but do lose their effectiveness with time and use if you’re using H2 blockers regularly — for example, more than two weeks — it’s sensible to speak to your doctor. 

Get Expert Help for Persistent Heartburn Symptoms 

If you’re dealing with persistent heartburn symptoms or ongoing digestive discomfort, it’s worth finding the underlying cause rather than relying on medication alone. A doctor may perform a gastroscopy to get a closer look at the stomach lining and esophagus. 

The Functional Gut Clinic offers specialist testing to identify what’s driving your reflux, ulcers, or indigestion — so you can get targeted treatment and lasting relief.