Lenamet is cimetidine, an H2 blocker that reduces stomach acid. It is used for heartburn, reflux, indigestion and stomach ulcers, and comes as 200 mg and 400 mg tablets and an injection. It works faster than a proton pump inhibitor but less powerfully — and it interacts with more medicines than almost anything else in the class.
What is Lenamet?
The South African Medicine Price Registry lists Lenamet in several forms containing cimetidine:
| Product | Schedule | Strength |
|---|---|---|
| Lenamet OTC | S2 | 200 mg tablet |
| Lenamet | S3 | 200 mg tablet |
| Lenamet | S3 | 400 mg tablet |
| Lenamet Injection | S3 | 200 mg/2 ml |
The 200 mg exists in two schedules. The S2 version is for occasional heartburn and indigestion, available from a pharmacy shelf; the S3 version requires a pharmacist’s involvement and is for more sustained treatment. Same medicine, different regulatory route.
Cimetidine is an H2-receptor antagonist (H2 blocker). Histamine is one of the signals that tells stomach lining cells to produce acid. Cimetidine blocks the H2 receptor those cells carry, reducing acid production.
Compared with a proton pump inhibitor, the trade-off is straightforward:
| H2 blocker (cimetidine) | PPI (omeprazole, pantoprazole) | |
|---|---|---|
| Onset | Within an hour | A day or two for full effect |
| Strength | Moderate | Strong |
| Duration | Several hours | Around 24 hours |
| Best for | Occasional or predictable heartburn | Sustained reflux, ulcer healing |
H2 blockers suit predictable or occasional symptoms — taken before a meal you know will cause trouble, or at night. PPIs suit persistent daily reflux and ulcer healing.
Tolerance develops. With continuous use over weeks, H2 blockers become noticeably less effective as the receptors adapt. This does not happen with PPIs, and it is why H2 blockers work best used intermittently.
Cimetidine is the oldest of the H2 blockers, and its distinguishing feature is unwelcome: it inhibits several liver enzymes that break down other medicines, so it raises the levels of a long list of them. Famotidine, a newer H2 blocker, does not do this and has largely replaced cimetidine for that reason. If you take several medicines, this matters, and it is worth asking whether famotidine would suit you better.
What is Lenamet commonly used for?
- Heartburn and acid indigestion, particularly occasional or predictable episodes.
- Gastro-oesophageal reflux disease, usually as a step below a PPI or alongside one at night.
- Stomach and duodenal ulcers, to heal them and prevent recurrence.
- Night-time acid breakthrough, added to a PPI — a specific and useful role, since the two work differently.
- Preventing stress ulcers, where the injection is used in hospital.
- Zollinger-Ellison syndrome, a rare acid-overproduction condition.
- Before anaesthesia, in some settings, to reduce stomach acid volume.
Take it before the trigger, not after. An H2 blocker reduces acid production, so taking it 30 to 60 minutes before a meal or at bedtime works far better than taking it once heartburn has started. For symptoms already present, an antacid is what helps — it neutralises acid immediately.
Persistent symptoms need a diagnosis. Regular heartburn most days for weeks is reflux disease, and is better managed with a proper assessment than with escalating self-treatment.
Lifestyle measures genuinely work: smaller meals, not lying down within three hours of eating, raising the head of the bed, losing excess weight, and cutting back alcohol, smoking and trigger foods.
How Lenamet fits into this medicine category
| Group | Examples | Notes |
|---|---|---|
| H2 blockers | Cimetidine (Lenamet), famotidine | Moderate, fast, short-acting; tolerance develops |
| Proton pump inhibitors | Pantoprazole, omeprazole, esomeprazole | Strongest; slow onset; for healing |
| Antacids | Gaviscon, Rennies | Neutralise acid present; act in minutes |
| Alginates | Gaviscon | Raft over stomach contents |
| Antispasmodics | Hyoscine (Hyospasmol) | Cramping, not acid |
| Anti-nausea | Metoclopramide (Adco-Contromet) | Nausea and stomach emptying |
See the digestive and stomach medicines hub.
What to check before using Lenamet
The interactions are the main issue with this particular medicine, and the reason to be more careful with it than with most acid treatments.
Tell your doctor or pharmacist if you take:
- Warfarin. Cimetidine raises its effect and bleeding risk substantially.
- Phenytoin, carbamazepine or theophylline — levels can rise to toxic ranges.
- Clopidogrel, whose activation may be reduced.
- Some antidepressants, including tricyclics and certain SSRIs.
- Benzodiazepines such as diazepam, whose sedation is prolonged.
- Antifungals such as ketoconazole or itraconazole, whose absorption falls when acid is reduced.
- HIV medicines, particularly atazanavir and rilpivirine.
- Metformin, propranolol, lidocaine, quinidine, ciclosporin or methadone.
Also tell them if you:
- Have kidney disease or liver disease — the dose usually needs reducing.
- Are elderly, where confusion is more likely.
- Are pregnant or breastfeeding.
- Are buying it for a child.
Do not treat alarm symptoms with acid suppression. See a doctor promptly rather than self-treating if you have difficulty or pain swallowing, unintentional weight loss, persistent vomiting, vomiting blood, black tarry stools, or anaemia, or if new indigestion begins over the age of 45 to 50.
Practical points:
- Take it 30 to 60 minutes before a meal, or at bedtime.
- Use it for occasional or short-term symptoms. Continuous use for more than a couple of weeks without advice is not the intended pattern.
- Space it from antifungals and iron by a couple of hours.
- Tell any new prescriber you are taking it — this is the medicine most likely to be forgotten and most likely to interact.
Possible cautions and when to ask a pharmacist or doctor
Common effects are usually mild: headache, dizziness, tiredness, diarrhoea, constipation and rash.
Cimetidine has one distinctive effect worth knowing about: it has a weak anti-androgen action and can cause breast tenderness or enlargement in men (gynaecomastia), and occasionally reduced libido or erectile difficulty. This is reversible on stopping, is more likely with higher doses and longer use, and does not happen with famotidine. It is a good reason to mention it rather than quietly stopping.
Seek medical advice promptly for:
- Confusion, agitation, hallucinations or unusual drowsiness — uncommon, but more likely in older people and those with kidney or liver problems.
- A slow heartbeat, palpitations or fainting.
- Yellowing of the skin or eyes, or dark urine.
- Unusual bruising, bleeding, or a sore throat with fever — possible effects on blood counts.
- Breast tenderness or swelling.
- A rash, particularly if widespread.
- Unusual bleeding on warfarin.
Get emergency help for vomiting blood, black tarry stools, severe chest pain, or swelling of the face, lips or tongue with difficulty breathing.
Chest pain deserves separate mention. Reflux and cardiac pain feel similar. Do not assume new or severe chest pain is heartburn — particularly with breathlessness, sweating, nausea, pain spreading to the arm, neck or jaw, or onset on exertion. Get it assessed.
Contact your doctor if symptoms do not improve within two weeks, if they return as soon as you stop, if you find yourself taking it most days, or if you take several other medicines — in which case famotidine or a PPI may be a better fit.
Related medicine guides
Frequently asked questions
What is Lenamet 400 mg used for? Reducing stomach acid — for heartburn, reflux, indigestion, and healing stomach and duodenal ulcers. It contains cimetidine.
What is Lenamet 200 mg used for? The same purposes at a lower strength. The 200 mg exists as both an over-the-counter product for occasional heartburn and a pharmacist-supplied version for more sustained use.
How is it different from omeprazole or pantoprazole? It works faster but less powerfully and for a shorter time. PPIs are better for daily reflux and ulcer healing; H2 blockers suit occasional or predictable symptoms.
When should I take it? Thirty to sixty minutes before a meal that usually triggers symptoms, or at bedtime. For heartburn already present, an antacid works faster.
Why does it seem to work less well over time? Tolerance develops with continuous use as the receptors adapt. H2 blockers work best used intermittently.
Does it interact with other medicines? More than most. Cimetidine raises the levels of many medicines, including warfarin, phenytoin and theophylline. Tell every prescriber you take it.
Can it cause breast swelling in men? Yes, uncommonly. Cimetidine has a weak anti-androgen effect. It reverses on stopping, and famotidine does not cause it.
How long can I take it? Short-term or intermittent use is the intended pattern. Symptoms lasting more than two weeks need assessment.