Proton pump inhibitor (PPI)Over the counter and by prescription

Losecomeprazole

Also sold as: Olex, Losec MUPS

The original proton pump inhibitor, used for reflux and ulcers. Available on prescription, and at 20 mg from the pharmacy counter for short courses.

Quick answer

What it is: A proton pump inhibitor — the first of the class — which disables the acid pumps in the stomach lining rather than neutralising acid already there.
What it's used for: Gastroesophageal reflux disease, erosive esophagitis, stomach and duodenal ulcers, H. pylori treatment, and frequent heartburn.
Worth knowing: Take it 30 to 60 minutes before your first meal. Capsules are swallowed whole; the coating is what gets it past stomach acid.
Main safety point: It reduces how well clopidogrel works. If you take clopidogrel, pantoprazole is usually the PPI chosen instead.

Not sure which option is right for you? Pill4Me pharmacists in Chilliwack can help.

Call 604-705-3644 Book a doctor

Drug class

Proton pump inhibitor (PPI)

Use in Canada

One of the most widely used acid reducers in Canada, on prescription and at the pharmacy counter

What is Losec?

Omeprazole reduces the amount of acid the stomach produces. It is used for gastroesophageal reflux disease and erosive esophagitis, for stomach and duodenal ulcers, as part of H. pylori eradication regimens, to protect the stomach in people taking long-term anti-inflammatories, and at 20 mg without a prescription for short-term treatment of frequent heartburn.

How Losec works

Omeprazole binds irreversibly to the proton pump in the cells lining the stomach, switching off acid secretion from each pump it reaches. New pumps are made continuously, which is why the effect builds over the first few days of treatment and why once-daily dosing works despite the drug itself clearing the body quickly.

Forms and strengths

Delayed-release capsules and tablets, commonly 10 mg, 20 mg and 40 mg. Losec MUPS tablets can be dispersed in water for people who cannot swallow capsules. Generic omeprazole is widely available and inexpensive.

How Losec is taken

Once daily, 30 to 60 minutes before the first meal of the day. Swallow capsules whole rather than crushing or chewing them. The non-prescription 20 mg product is labelled for a 14-day course. On prescription, dose and duration depend on what is being treated — a short course for reflux, longer where ulcers are healing or stomach protection is needed.

This is general information, not a dose for you. Dosing depends on the reason you are taking it, your kidney and liver function, your age, and everything else you take — follow the directions on your own label, and ask us if they differ from what you read here.

If you miss a dose

Take it when you remember on the same day, ideally before a meal. If the next dose is nearly due, skip the one you missed rather than taking two. A single missed dose may bring symptoms back briefly but does not reset your treatment.

Side effects

Common — usually manageable

Headache
Diarrhea or constipation
Nausea
Abdominal pain or bloating
Wind
Dizziness

Get medical help for these

Persistent watery diarrhea with fever or cramping — get assessed, as acid suppression raises the risk of C. difficile
Muscle cramps, tremor, irregular heartbeat or seizures — possible signs of low magnesium with long-term use
Reduced urine output, swelling or unexplained tiredness — rare kidney inflammation has been reported with PPIs
Rash on sun-exposed skin, reported as a lupus-like reaction
Severe allergic reaction: facial swelling, wheeze, widespread hives

Important warnings

If you take clopidogrel, do not start omeprazole without checking — it reduces clopidogrel's antiplatelet effect. Pantoprazole is the usual alternative.

The non-prescription version is a 14-day course. Repeat courses without an assessment are not what it is designed for.

Take it before food — a PPI on a full stomach is substantially less effective.

Stopping a long course abruptly can cause rebound acid for a few weeks. Taper, or step down to famotidine, rather than stopping outright.

Difficulty swallowing, vomiting blood, black stools or unintended weight loss need assessment, not a higher dose.

Who should take extra care

People taking clopidogrel: The interaction is well documented — pantoprazole is generally used instead.
People taking warfarin: Omeprazole can raise INR, so monitoring is adjusted after starting or stopping it.
Long-term users: Vitamin B12 and magnesium levels are worth checking periodically on extended treatment.
Liver impairment: Doses are reduced in significant liver disease.
Pregnancy and breastfeeding: Discuss with your prescriber — reflux in pregnancy is common and there are appropriate options.
Older adults: Higher baseline risk of C. difficile and fractures makes indefinite use worth reviewing.

Who should not take it

Known allergy to omeprazole or other proton pump inhibitors
Combination with rilpivirine or nelfinavir (HIV medications)

Drug interactions

Clopidogrel — omeprazole inhibits CYP2C19 and reduces clopidogrel's activation; pantoprazole is the usual substitute. Rilpivirine and nelfinavir must not be combined with it. Warfarin — INR can rise. Atazanavir, ketoconazole, itraconazole and some iron salts need stomach acid to be absorbed and become less effective. Methotrexate levels can rise at high doses. Citalopram, diazepam, phenytoin, digoxin and tacrolimus levels can all be affected. Levothyroxine absorption may change, making a TSH recheck reasonable after starting.

Commonly asked about alongside Losec: Nexium, Pantoloc, Pepcid.

This is not a complete list. If you take several medications, or buy anything over the counter, a pharmacist medication review is the reliable way to catch interactions that matter.

Coverage in British Columbia

Generic omeprazole is inexpensive, and prescription versions are commonly covered subject to your PharmaCare plan, your indication and Low Cost Alternative pricing. The non-prescription 20 mg product bought at the counter is generally not a PharmaCare benefit. Ask us to check what applies to you — 604-705-3644.

Coverage may depend on indication, PharmaCare plan and Special Authority requirements. Ask Pill4Me Pharmacy to check your coverage, or see BC PharmaCare.

Frequently asked questions

Can I buy omeprazole without a prescription in Canada?

Omeprazole 20 mg for the short-term treatment of frequent heartburn is available without a prescription, but it is kept behind the pharmacy counter — you ask a pharmacist rather than picking it off a shelf. It is labelled for a 14-day course. Higher strengths, longer treatment, and use for ulcers or erosive esophagitis all require a prescription.

Why can't I take omeprazole with clopidogrel?

Clopidogrel is a prodrug — it has to be converted to its active form by the liver enzyme CYP2C19, and omeprazole inhibits that enzyme. The concern is that clopidogrel becomes less effective at preventing clots, which matters a great deal in someone who has had a stent or a heart attack. Pantoprazole has much less effect on that enzyme and is the PPI usually chosen instead. If you are already on both, raise it with us rather than stopping anything.

How long does omeprazole take to work?

Some relief often comes within a day, but the full effect takes about three to four days to build as more acid pumps are blocked. It is not the right choice for a single episode of heartburn — an antacid works in minutes and famotidine within about an hour. A PPI is for frequent symptoms or for healing damage.

What happens if I stop taking omeprazole?

After a short course, usually nothing. After a long one, acid production can rebound above its original level for a few weeks, which feels like the reflux coming back worse and often leads people to restart when they did not need to. Tapering the dose, or stepping down to famotidine for a couple of weeks, generally avoids that. A pharmacist can plan it with you.

Is omeprazole covered by BC PharmaCare?

Prescription omeprazole is commonly covered, but coverage depends on the product, your indication and your PharmaCare plan, and Low Cost Alternative pricing applies to this class. The non-prescription version you buy at the counter is generally not covered. Call 604-705-3644 with your prescription and we will confirm what you would pay before dispensing.

Related medications

Nexium (esomeprazole magnesium)Pantoloc (pantoprazole sodium)Pepcid (famotidine)

Conditions it’s used for

Acid Reflux & GERD

Not sure which option is right for you?

You don't need an appointment to ask. Our pharmacists can check this against your other medications and your health history, in the store or over the phone — there's no charge for the conversation.

Call 604-705-3644 Minor ailments service Transfer my prescription

Pill4Me Pharmacy is at 5625 Promontory Rd Unit 101, Chilliwack, BC. We deliver free to Chilliwack, Sardis, Promontory, Vedder and Yarrow, and you can reach a pharmacist directly at 604-705-3644.