Best Probiotics for Constipation: 8 Strains Ranked (2026)

Yes — probiotics can help constipation, but only certain strains do. The best probiotics for constipation are Bifidobacterium lactis strains that speed colonic transit: HN019 has the strongest clinical evidence, followed by BB-12 and DN-173 010. Pooled across randomized trials, probiotics add roughly 1.3 bowel movements per week and improve stool consistency versus placebo.^[1] Most responders notice a change in 1–2 weeks, with full effect around 4 weeks. Strains outside this group — including most Lactobacillus acidophilus products — have much weaker constipation-specific evidence.

Best probiotics for constipation: strain comparison

Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Chronic constipation can indicate underlying health conditions that require professional evaluation. Always consult a qualified healthcare provider before starting any new supplement regimen, especially if you have existing health conditions or take medications.

Chronic idiopathic constipation affects a pooled 14% of adults in community studies, is about twice as common in women, and rises with age.^[10] This guide ranks the strains with real trial data, explains where each one actually works, and is honest about where the evidence runs out. For the underlying biology, see our chronic constipation and the microbiome hub.

How probiotics may help with constipation

The gut microbiome plays a significant role in regulating bowel function. Research has identified several mechanisms through which probiotics may improve constipation^[1]:

• Colonic transit time reduction: Certain strains appear to accelerate the movement of stool through the colon by influencing enteric nervous system signaling
• Short-chain fatty acid production: Probiotic bacteria produce SCFAs like butyrate and propionate, which stimulate colonic motility and increase water content in stools
• pH modulation: Lactic acid and other organic acids produced by probiotics lower colonic pH, which may stimulate peristalsis
• Gas production regulation: Some strains reduce excessive methane production, which has been linked to slowed transit and constipation
• Bile acid metabolism: Probiotics can modify bile acid profiles, influencing fluid secretion in the colon

A 2014 systematic review and meta-analysis found that probiotics significantly increased stool frequency by an average of 1.3 bowel movements per week and improved stool consistency compared to placebo.^[1]

The 8 best probiotic strains for constipation

1. Bifidobacterium lactis HN019 — strongest evidence

Evidence: strongest overall, though not uniformly positive | Dose: 1.8–17.2 billion CFU/day | Timeline: 1–2 weeks

B. lactis HN019 has the most robust clinical evidence for constipation relief. A dose-response trial demonstrated that both high-dose (17.2 billion CFU) and low-dose (1.8 billion CFU) supplementation significantly reduced whole gut transit time, with the higher dose producing faster results.^[2]

A larger 28-day dose-ranging trial in 228 adults with Rome III functional constipation is an important qualifier: it found no significant difference in colonic transit time, its primary outcome, or in secondary symptom measures such as bloating and straining. A post hoc analysis of the 65 participants with fewer than three bowel movements per week did show significantly higher bowel movement frequency on HN019 than placebo.^[11] Read together, the evidence suggests HN019 helps most in people whose main problem is genuinely low stool frequency, rather than in everyone who feels constipated.

How it works: HN019 appears to enhance motility through increased SCFA production and modulation of serotonin signaling in the enteric nervous system. Roughly 90% of the body's serotonin is produced in the gut, and it is a key trigger for peristalsis.

2. Bifidobacterium lactis BB-12 — best-studied for defecation frequency

Evidence: moderate–strong | Dose: 1–10 billion CFU/day | Timeline: 2–4 weeks

B. lactis BB-12 is one of the most extensively studied probiotic strains worldwide. A randomized, double-blind trial in otherwise healthy adults with low defecation frequency and abdominal discomfort found that BB-12 significantly increased bowel movement frequency versus placebo.^[3] Worth noting that this population was not diagnosed with functional constipation, so the result speaks to regularity more directly than to treating established constipation.

How it works: BB-12 produces lactic and acetic acid that lower colonic pH, promoting peristaltic activity, and supports resident Bifidobacterium populations that are consistently depleted in constipated people.

3. Bifidobacterium lactis DN-173 010 — the fermented-milk strain

Evidence: moderate–strong | Dose: delivered in fermented milk | Timeline: 10 days–4 weeks

In a double-blind crossover trial, 36 healthy women consuming three 125 g cups per day of fermented milk containing DN-173 010 had significantly shorter total and sigmoid colonic transit times than during the control period.^[4] Notably, the effect was not explained by changes in fecal bacterial mass or bile acids — this strain appears to act on motility directly.

DN-173 010 is the organism sold in Activia under the marketing names Bifidus ActiRegularis (Europe) and Bifidus Regularis (North America), which is why the food and the strain are effectively the same recommendation.

4. Bifidobacterium longum BB536 — for older adults

Evidence: moderate, with an important caveat | Dose: 5 × 10¹⁰ CFU/day | Timeline: 4 weeks

In a randomized controlled trial of 80 older adults (mean age 78) with chronic constipation, B. longum BB536 missed its primary endpoint on total constipation score (P = 0.074). However, it produced a significant improvement in the stool frequency subscale versus placebo, and a trend toward less failure of evacuation.^[5]

That is a genuinely mixed result, and worth knowing before you buy: BB536 is a reasonable choice if age-related slowing is the issue, but it is not in the same evidence tier as HN019.

5. Bacillus coagulans Unique IS2 — best for stool consistency

Evidence: moderate | Dose: 2 billion CFU/day | Timeline: 4 weeks

In a double-blind, placebo-controlled trial of 100 adults with functional constipation, B. coagulans Unique IS2 at 2 billion CFU once daily significantly increased bowel movements versus placebo over four weeks. 98% of the probiotic group reached normal stool consistency, versus 74% on placebo, with reported relief from incomplete evacuation and painful defecation.^[6]

B. coagulans is spore-forming, so it survives stomach acid and does not need refrigeration — practical if you travel or store supplements at room temperature.

6. Lactobacillus casei Shirota — genuinely mixed evidence

Evidence: mixed | Dose: ~6.5 billion CFU per 65 mL serving | Timeline: 2–4 weeks

L. casei Shirota is the strain in Yakult. In a four-week trial of 70 people with chronic constipation, a 65 mL daily beverage significantly improved self-reported constipation severity and stool consistency from week two, and 89% of the probiotic group reported a positive effect versus 56% on placebo.^[7]

A later, larger randomized trial in adults with Rome II functional constipation was essentially null: constipation severity and stool frequency improved in both groups, with no significant advantage over placebo at the conventional threshold, and only a small effect on stool consistency that grew over time.^[12]

Two well-run trials disagreeing is a fair reason to place Shirota below the Bifidobacterium strains rather than alongside them.

7. Lactobacillus rhamnosus GG — broad support, thin constipation data

Evidence: moderate but indirect | Dose: ~10 billion CFU/day | Timeline: 2–4 weeks

L. rhamnosus GG is the most studied probiotic strain overall and is the organism in Culturelle. Its constipation-specific evidence is weaker than HN019's, though it is included among strains contributing to improved stool frequency and transit in pooled analyses.^[8] It is a defensible general-purpose choice, not a targeted constipation choice.

8. Lactobacillus reuteri DSM 17938 — strongest in infants

Evidence: good in infants, limited in adults | Dose: 10⁸ CFU/day in infant trials | Timeline: 2–4 weeks

In a placebo-controlled trial of 44 infants aged 6 months and older with functional chronic constipation, L. reuteri DSM 17938 significantly increased bowel movement frequency at weeks 2, 4, and 8 — but did not significantly improve stool consistency versus placebo.^[9] A systematic review of probiotics for functional constipation in children concluded that the pediatric evidence overall remains limited and does not yet support routine use.^[13] Adult constipation data for this strain is sparse.

What about L. acidophilus?

Lactobacillus acidophilus appears in a large share of supermarket probiotics, which is probably why people search for it. Its constipation evidence is weak. In the main meta-analysis of functional constipation, the pooled benefit on stool frequency and consistency was significant for B. lactis but not for the one Lactobacillus strain analysed separately, L. casei Shirota — and L. acidophilus was not assessed as a subgroup at all.^[1] An acidophilus blend is not a bad product; it is simply the wrong tool if constipation is the specific problem you are solving.

What about E. coli Nissle 1917?

Escherichia coli Nissle 1917 is a well-characterized probiotic strain, but its modern controlled data sits in irritable bowel syndrome rather than constipation. A 12-week randomized trial in 120 IBS patients found a higher responder rate than placebo, with the clearest benefit in people whose symptoms began after gastroenteritis or antibiotics — no significant benefit in other subgroups.^[14] Treat it as a niche option, not a constipation first-line.

Which probiotics soften stool?

Hard stool is a water problem. The longer stool sits in the colon, the more water is reabsorbed — so anything that speeds transit tends to soften what you pass. Probiotics act on both sides of this: transit-active Bifidobacterium strains reduce colonic residence time, and SCFA production increases the osmotic pull of water into the lumen.

In practice:

• Best consistency evidence: B. coagulans Unique IS2, where 98% of the treated group reached normal stool consistency versus 74% on placebo.^[6]
• Best transit evidence: B. lactis HN019 and DN-173 010, which shorten measured gut transit time.^[2][4]
• Overall: pooled meta-analysis confirms improved stool consistency across probiotic trials, not just frequency.^[1]

A useful way to track this is the Bristol Stool Scale: the goal is a shift from types 1–2 (hard lumps, lumpy sausage) toward types 3–4. If your problem is straining with hard stool rather than infrequency, softening is what you are actually chasing, and pairing a probiotic with psyllium husk and enough fluid usually moves it faster than either alone.

Best probiotics for chronic constipation

Chronic constipation is not one condition, and the strain that helps depends on which subtype you have:

• Normal-transit functional constipation — the most common form, where transit is measurably normal but stools feel hard or difficult. This is where probiotics do best. Start with HN019.
• Slow-transit constipation — genuinely delayed colonic movement. Transit-active strains (HN019, DN-173 010) are the rational choice, and this is the subtype where prescription prokinetics are most often needed alongside.
• Defecatory disorders / pelvic floor dyssynergia — the colon works; the outlet does not coordinate. Probiotics will not fix this. It responds to anorectal biofeedback and physical therapy, and treating it as a supplement problem wastes months.

For chronic cases specifically, B. coagulans Unique IS2 is worth knowing about because its trial enrolled adults with established functional constipation and reported both frequency and consistency outcomes at four weeks.^[6] In older adults, BB536 improved stool frequency although it missed its primary endpoint.^[5]

A broader meta-analysis covering both chronic idiopathic constipation and IBS-C found probiotics beneficial overall, but noted that the quality of individual trials varies considerably.^[15] If constipation has persisted beyond three months, get evaluated rather than cycling through supplements — and if bloating and methane are prominent, the SIBO and IMO protocol covers methane-associated slow transit in more detail.

If your constipation comes with recurrent abdominal pain and meets Rome IV criteria, you are dealing with IBS-C rather than simple constipation, and the strain shortlist is different — see the best probiotics for IBS for the IBS-C section and the transit-time evidence behind B. lactis HN019.

Probiotic foods for constipation

Fermented foods deliver live organisms alongside food matrix effects, and two of them contain the exact strains discussed above:

• Activia — contains B. lactis DN-173 010, the strain shown to shorten colonic transit time.^[4] The trial used three servings daily, which is more than most people eat.
• Yakult — contains L. casei Shirota, with one positive and one null constipation trial.^[7][12]
• Kefir — a broader live-culture mix than yogurt, typically containing both bacteria and yeasts. Constipation-specific trial evidence is limited, but it is a reasonable dietary base.
• Yogurt with live active cultures — check the label for a named strain; most yogurts supply S. thermophilus and L. bulgaricus, which are not transit strains.
• Sauerkraut, kimchi, miso — unpasteurized versions supply live lactic acid bacteria plus fiber. Pasteurized shelf-stable versions do not.

Food is not a strict substitute for a characterized supplement — a capsule tells you the strain and dose, and a jar usually does not. But if you would rather eat than supplement, choose the products with named strains. Our probiotic foods guide covers the full list and how to read labels.

Probiotics for constipation in women

Constipation is not evenly distributed. In a meta-analysis of 41 population studies covering more than 261,000 people, chronic idiopathic constipation was roughly twice as common in women (OR 2.22, 95% CI 1.87–2.62) and became more common with age.^[10]

Two physiological patterns explain much of the difference:

• Cycle-related slowing. Gut transit tends to slow during the luteal phase, when progesterone is high — which is why constipation for many women is cyclical rather than constant.
• Pregnancy. Sustained progesterone plus mechanical pressure and iron supplementation make constipation one of the most common complaints of pregnancy. Discuss any supplement with your provider first.

There is no female-specific probiotic strain, but it is worth noting that the DN-173 010 transit evidence was generated in women specifically, in a controlled crossover design.^[4] For broader life-stage considerations, see our guide to probiotics for women.

Prebiotics vs. probiotics for constipation

These are different tools and the distinction matters more here than in most gut topics:

Fiber is the more reliable first move for most people, and psyllium in particular has the most consistent bulk-forming evidence. Probiotics are the sensible addition when adequate fiber and fluid alone have not resolved things, or when transit rather than bulk is the limiting factor. A pooled analysis covering prebiotics, probiotics, and synbiotics in chronic idiopathic constipation supports both categories, with variation across individual trials.^[15]

If you want the full comparison, see prebiotics vs. probiotics.

Do brand-name probiotics help? Matching strains to products

Supplement marketing rarely leads with the strain code, which is the only part that predicts whether a product matches the trials:

The practical rule: ignore the brand, read the strain code on the label. "Bifidobacterium lactis" alone tells you nothing — HN019, BB-12, and DN-173 010 are all B. lactis, and they were tested separately. If a product will not name its strain designations, it has not been tested at all. Our strain comparison guide and supplement buyer's guide go deeper on label reading.

How to use probiotics for constipation

Dosage guidelines

Trials showing benefit generally used 1 to 20 billion CFU per day of a single well-characterized strain, taken once daily. Higher is not automatically better: the HN019 dose-response trial found benefit at both 1.8 and 17.2 billion CFU per day.^[2] Strain identity predicts results far better than total CFU count — see our CFU guide for how to interpret label numbers.

Timing and administration

• Take with food: A meal containing some fat improves probiotic survival through stomach acid
• Consistency matters: Daily use is essential — most probiotic bacteria do not permanently colonize the gut
• Morning timing: Some practitioners suggest morning dosing to align with natural circadian patterns of gut motility
• Adequate hydration: Always pair probiotic use with sufficient water, as dehydration is a primary constipation driver
• Travel: Irregularity is common when routine and time zones change. Spore-forming B. coagulans is the easiest to carry, since it does not require refrigeration
• Older adults: Bifidobacterium populations decline with age and constipation prevalence rises accordingly^[10] — BB536 and BB-12 are the reasonable picks

What to expect: timeline

Constipation is one of the faster-responding uses for probiotics. For the equivalent timelines across other goals — and for guidance on how long it takes for probiotics to work and how long a course should run — see our full probiotic timeline guide.

Combining probiotics with other approaches

Probiotics work best alongside the fundamentals^[15]:

• Fiber — 25–35 g/day, increased gradually. Soluble sources such as psyllium husk, oats, and inulin are the most useful for constipation.
• Hydration — fiber without adequate fluid can make hard stool worse, not better. Aim for roughly 2 litres daily, more if active or in a warm climate.
• Physical activity — 20–30 minutes of moderate walking stimulates colonic motility.
• Prebiotic foods — garlic, onions, leeks, asparagus, slightly green bananas, and Jerusalem artichokes feed the Bifidobacterium populations the strains above are trying to support.

If you want to keep a consistent rhythm rather than treat an active problem, our companion guide on probiotics for regularity covers maintenance.

When probiotics may not be enough

Probiotics address one component of constipation. Several common causes need something else entirely:

• Medications: Opioids, some antidepressants, iron supplements, and calcium channel blockers commonly cause constipation
• Pelvic floor dysfunction: Requires biofeedback and physical therapy, not supplements
• Hypothyroidism: Requires thyroid hormone replacement
• Slow-transit constipation: May need prescription prokinetic medication
• Structural abnormalities: Require gastroenterological evaluation

Seek medical evaluation before relying on probiotics if constipation is severe or persistent, or if it comes with blood in the stool, unintentional weight loss, anemia, or a new unexplained change in bowel habits after age 50.

What the evidence shows — and its limits

A systematic review confirmed that probiotic-containing products improve stool frequency and intestinal transit time in constipated adults.^[8] The important qualifications:

• Strain variability: Not all probiotics help constipation — strain selection matters enormously, and most retail products are not built around a tested constipation strain
• Study quality: Many trials are small (under 100 participants) and industry-funded
• Mixed results within strains: even HN019 has a large trial that missed its primary transit endpoint; Shirota has one clearly positive and one null trial; BB536 missed its primary endpoint
• Publication bias: after statistical adjustment for it, one meta-analysis saw the pooled gain in weekly stool frequency fall from 0.83 to 0.30 bowel movements^[8]
• Individual variation: Response is highly individual, shaped by baseline microbiome, diet, and transit type
• Temporary effects: Benefits generally require ongoing use — most strains do not permanently colonize the gut

Practical recommendations

For most adults with functional constipation, a reasonable evidence-based sequence is:

1. First-line: Optimize fiber (25–35 g/day), fluid intake, and physical activity
2. Add a targeted probiotic: Start with B. lactis HN019, or BB-12 if HN019 is unavailable
3. Match the trial dose: 1–20 billion CFU once daily of a single named strain
4. Allow adequate time: Give it 4 weeks of consistent daily use before judging
5. Track your response: Log stool frequency and Bristol Stool Scale consistency, not just how you feel
6. Switch strain, then escalate: If nothing changes by 4–6 weeks, try a different mechanism (B. coagulans Unique IS2 for consistency) and see a gastroenterologist rather than adding more products

For broader context, see our guides to digestive health, beneficial probiotic bacteria, and emerging next-generation probiotic strains.

---

This article was reviewed for medical accuracy and reflects evidence available as of the last updated date. Probiotic research is a rapidly evolving field — recommendations may change as new evidence emerges.