Probiotics
Worth taking during a course of antibiotics. For irritable bowel and general gut health, the evidence is weak.
At a glance
| Our verdict | During antibiotics (prevents C. difficile, 1 in 42 helped). For irritable bowel, low to very low certainty. |
| Best use | During antibiotics; irritable bowel |
| How sure the evidence is | Moderate with antibiotics; Low to Very low for irritable bowel |
| Cost a month | About $30 to $60 |
Written for adults in Canada. It explains the evidence; it is not advice for you personally. Last reviewed 20 October 2026.
Supplement Check
Is it right for you?
Probiotics are live organisms, and for some people they are not safe: a weak immune system, a central line, pancreatitis. Your check asks before it suggests one, and tells you when it is worth it. Our Supplement Check looks at:
- A weakened immune system (immunosuppression), or a low white-cell count (neutropenia)
- A central venous catheter (central line)
- Short bowel
- Critical illness
- Pancreatitis
- Every medicine you take
Coming soon. The Supplement Check and the Online Health Assessment open once our safety testing is complete.
$59 when it opens, paid once. Adults 18 and over, anywhere in Canada. While the service is new, Dr. French reads every report himself, and your report arrives within 3 working days. More about the Supplement Check
What it is
Probiotics are live microorganisms: bacteria, or a yeast (Saccharomyces boulardii). Their effects depend on the strain, so one product's results do not carry over to another. The number of live organisms that matters is the count at the expiry date, not at manufacture. Choose a product with a Canadian licence (NPN) and refrigerate it if the label says so.
How it acts
They may crowd out harmful bacteria (colonisation resistance), signal to the immune system, and change bile acids and the short-chain fatty acids made in the bowel. This is mechanism; the trials are the evidence.
What it is used for, and what the evidence says
Sold for diarrhoea with antibiotics, prevention of Clostridioides difficile (C. difficile) infection, irritable bowel and constipation.
| Use | What the trials found | How sure we are |
|---|---|---|
| During antibiotics: C. difficile | A Cochrane review of 31 trials in 8,672 people: C. difficile diarrhoea in 1.5% with a probiotic against 4.0% without, so about 1 in 42 people was helped. The benefit was clear where the risk was above 5% (about 1 in 12 helped) and not shown where the risk was lower. The review rated the evidence moderate. [1] | Moderate |
| During antibiotics: diarrhoea in children | Antibiotic-related diarrhoea in 8% of children taking a probiotic against 19% without: 1 child in 9 helped. [2] Adult data are similar but weaker. | Moderate |
| Irritable bowel | Some strains may help, but certainty was low to very low across almost all analyses. [3] Which strain, for whom, is not established. | Low to Very low |
| General gut health | Little evidence for taking probiotics for general “gut health”. | Very low |
| Constipation | It is sold for this. Our review did not grade trials for it. | Not reviewed |
How sure we are: High means further research is very unlikely to change the answer; Moderate, it might; Low, it may well change; Very low, we are very unsure. These follow the GRADE method that guideline panels use.
Benefits
- Fewer cases of C. difficile during antibiotics: 1 in 42 helped. [1]
- Less antibiotic-related diarrhoea in children: 1 in 9 helped, moderate certainty. [2]
- Irritable bowel: possible benefit from some strains, low to very low certainty. [3]
Risks and side effects
- Bloodstream infection with the probiotic bacteria or yeast, in people with a weak immune system, a central venous line, or critical illness.
- Severe acute pancreatitis: more deaths with probiotics in a trial (PROPATRIA). [9]
- Variable products. Live counts fall over time; check the count at expiry.
Interactions with medicines
Our review found no effect on the liver enzymes that clear medicines. The interactions are with medicines that kill the organisms, and with medicines that weaken the immune system.
| Medicine | What can happen | What to do |
|---|---|---|
| Antibiotics | Kill bacterial probiotics taken at the same time | Take a bacterial probiotic 2 hours apart from the antibiotic |
| Antifungal medicines | Kill Saccharomyces boulardii (antibiotics do not) | Choose a bacterial probiotic, spaced 2 hours from the antibiotic |
| Immunosuppressants | Risk of infection with the probiotic organism | Do not take |
Who should not take it
- A weakened immune system (immunosuppression), or a low white-cell count (neutropenia).
- A central venous catheter (central line).
- Short bowel.
- Critical illness.
- Pancreatitis.
- Prosthetic heart valve: caution, discuss with your doctor.
- Under 18: outside the Supplement Check.
Dose and timing
- The product's own dose: doses are strain-specific.
- Start with the antibiotic and continue during the course and for 1 week after.
- Bacterial probiotics: take 2 hours apart from the antibiotic.
- Store as the label says (refrigerate if labelled); check the live count at expiry.
- Irritable bowel: only on Dr. French's decision, one strain-specific product for 4 to 8 weeks, with an IBS symptom score or a symptom diary before and after. If nothing has changed, stop.
What we know about Canadians
No Canadian data on probiotic use, C. difficile or irritable bowel in our review. Nearly half of Canadians (45.6%) took at least one supplement in 2015. [4]
How sure are we: not graded. Our Canadian population review did not cover probiotics or bowel conditions; the one figure is general supplement use (Statistics Canada, 2015).
An honest comparison: irritable bowel symptoms
Warning signs first (weight loss, bleeding from the bowel, anaemia, a new change in bowel habit after 50, symptoms that wake you at night, or a family history of bowel cancer or coeliac disease): they go to a doctor, not to this table. Cost a month in Canadian dollars.
| Option | Effect | How sure we are | Cost a month (CAD) |
|---|---|---|---|
| Peppermint oil, enteric-coated | 37% fewer people left without improvement (relative risk 0.63); ranked first for overall symptoms [7] | Low | $15 to $25 |
| Probiotics | Some strains may help; uncertain across almost all analyses [3] | Low to Very low | $30 to $60 |
| Soluble fibre, built up slowly (the trials used psyllium; we use barley beta-glucan first, oat beta-glucan if you avoid gluten, and psyllium only with published heavy-metal results) | 17% fewer people still had symptoms (relative risk 0.83): 1 in 7 helped; bran did not help [5] | Moderate | $10 to $15 |
| Low FODMAP diet with a dietitian, then foods brought back | Ranked first for pain, bloating and bowel habit; unblinded, specialist settings [6] | Low | Dietitian $30 to $60 |
| Gut-directed psychological therapy (CBT, hypnotherapy) | Effective in trials (not pooled in our review) | Moderate | $0 to $200 |
| Low-dose amitriptyline, 10 to 30 mg at night | 27 points lower on the IBS symptom severity score than placebo at 6 months [8]; tricyclics ranked first for pain [7] | High | $8 to $10 |
Read honestly: for irritable bowel, probiotics cost the most of the supplements here and have the weakest evidence; soluble fibre and peppermint oil come first. During antibiotics the picture is different: our review compared no lifestyle option or medicine for that use, and there the probiotic is worth taking.
Our verdict
Recommended during a course of antibiotics, for adults without the risks listed above: the product's own dose, during and for 1 week after the antibiotic, spaced 2 hours from it.
For irritable bowel, only on Dr. French's decision, as a 4 to 8 week trial of one product after fibre and peppermint oil. Not for general gut health.
During antibiotics there is a measured benefit: fewer cases of C. difficile (1 in 42) and less diarrhoea in children (1 in 9). For irritable bowel the evidence is low to very low certainty and the effects depend on the strain, while soluble fibre and peppermint oil do better for less money. Probiotics are live organisms, so we ask about the immune system, central lines and pancreatitis first.
Supplement Check
Before you buy it, get it checked
Probiotics are live organisms, and for some people they are not safe: a weak immune system, a central line, pancreatitis. Your check asks before it suggests one, and tells you when it is worth it. Our Supplement Check looks at:
- A weakened immune system (immunosuppression), or a low white-cell count (neutropenia)
- A central venous catheter (central line)
- Short bowel
- Critical illness
- Pancreatitis
- Every medicine you take
Coming soon. The Supplement Check and the Online Health Assessment open once our safety testing is complete.
$59 when it opens, paid once. Adults 18 and over, anywhere in Canada. While the service is new, Dr. French reads every report himself, and your report arrives within 3 working days. More about the Supplement Check
Disclosure of financial interest
White Pine Medical earns money from products bought through our Fullscript dispensary. Dr. French's Code of Ethics requires him to tell you this. You do not have to buy anything from us: every product is named by its ingredient and dose so you can buy it at any pharmacy, and the advice is the same wherever you buy it, or if you buy nothing.
References
- Goldenberg JZ, Yap C, Lytvyn L, Lo CK, Beardsley J, Mertz D, et al. Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children. Cochrane Database Syst Rev. 2017;12(12):CD006095. PMID 29257353.
- Guo Q, Goldenberg JZ, Humphrey C, El Dib R, Johnston BC. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Syst Rev. 2019;4(4):CD004827.
- Goodoory VC, Khasawneh M, Black CJ, Quigley EMM, Moayyedi P, Ford AC. Efficacy of probiotics in irritable bowel syndrome: systematic review and meta-analysis. Gastroenterology. 2023;165(5):1206-18.
- Statistics Canada. Use of nutritional supplements, 2015. Health Fact Sheets 82-625-X. 20 Jun 2017. https://www150.statcan.gc.ca/n1/pub/82-625-x/2017001/article/14831-eng.htm
- Moayyedi P, Quigley EM, Lacy BE, Lembo AJ, Saito YA, Schiller LR, et al. The effect of fiber supplementation on irritable bowel syndrome: a systematic review and meta-analysis. Am J Gastroenterol. 2014;109(9):1367-74.
- Black CJ, Staudacher HM, Ford AC. Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis. Gut. 2022;71(6):1117-26.
- Black CJ, Yuan Y, Selinger CP, Camilleri M, Quigley EMM, Moayyedi P, et al. Efficacy of soluble fibre, antispasmodic drugs, and gut-brain neuromodulators in irritable bowel syndrome: a systematic review and network meta-analysis. Lancet Gastroenterol Hepatol. 2020;5(2):117-31.
- Ford AC, Wright-Hughes A, Alderson SL, Ow PL, Ridd MJ, Foy R, et al. Amitriptyline at low-dose and titrated for irritable bowel syndrome as second-line treatment in primary care (ATLANTIS): a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet. 2023;402(10414):1773-85.
- Besselink MG, van Santvoort HC, Buskens E, Boermeester MA, van Goor H, Timmerman HM, et al. Probiotic prophylaxis in predicted severe acute pancreatitis: a randomised, double-blind, placebo-controlled trial. Lancet. 2008;371(9613):651-9. PMID 18279948.
Costs marked as estimates are typical Canadian retail or pharmacy prices, before any drug plan. Certainty grades are ours unless the review gave its own.