How Long Does it Take for Probiotics to start working?

Everyone’s taking probiotics these days. At least, it seems that way: they now command an estimated $37 billion market worldwide. Maybe the growing stack of research connecting our microbiomes to an ever-increasing list of diseases, ranging from obesity to IBS and depression, has something to do with it.

There’s still a lot we don’t know about the microbiome. While probiotics are helpful for many of us, if you’re looking for concrete evidence they’ll work for your gut issues, you’re unlikely to find it. Read on to find out what to expect on your quest for the perfect probiotic.

Learn more about your gut health. Talk to our experts.



Do Probiotics Even Work?
How Long Does it Take for Probiotics to Start Working?
How Do You Know if a Probiotic is Working?
What Happens to Your Body When You Start Taking Probiotics?
Is it OK to Take a Probiotic Every Day?
What are the Side Effects of Too Many Probiotics?
How Long Should You Take Probiotics?
Key takeaways

Do probiotics even work?

Probiotics do work in certain circumstances, but we need more research. More and more clinical trials are taking place to explore the effects different probiotics have on a huge array of health conditions.

For instance, we know from meta-analyses (research that analyses research) that certain strains (types) of probiotics provide benefits for infectious and antibiotic-associated diarrhoea (Source: NCBI). Some GPs now recommend taking these strains to their patients who complain of diarrhoea during a course of antibiotics. However a recent study in the journal Cell found that taking probiotics after antibiotics could prevent or slow down the return of the bacterial families lost as a result of the treatment (Source: CELL).

Interestingly, a group of people in the study who received autologous faecal microbiota transplantation (their pre-treatment stools were kept and reintroduced into their colons after the course of antibiotics) recovered their microbiota the quickest, with the composition of the microbiota returning to normal within days. These researchers found that bacteria re-grew in the test subjects’ colons in very different ways, with some people’s guts rejecting the new guys and others allowing them to set up shop with no issues.

Essentially, this means that for some people, taking certain probiotic supplements is a waste of time and money, while for others, the same probiotics can be very effective. Right now, there’s no way to predict how you’ll react to any probiotic, so your best bet is to start low and go slow (Skip to ‘How Do You Know a Probiotic is Working’ below for more on side effects to watch out for).

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Probiotics for IBS

Many ‘IBS diets’ recommend probiotics. Although probiotics aren’t a recognised IBS treatment, many people with IBS claim that they help to alleviate their symptoms better than any IBS medication.

Responses to probiotics are different for every IBS sufferer. A group of people with exactly the same symptoms are all likely to have completely different responses to the same probiotic. We don’t know exactly why this is, but it’s likely to have something to do with the microbes that already live in their guts.

According to a recent review of 11 studies, in general the following strains appear to be the best IBS probiotics (Source: NCBI).

  • Lactobacillus acidophilus
  • Streptococcus thermophilus
  • Bifidobacterium breve
  • Bifidobacterium longum

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Infographic how long does it take for probiotics to start working

How long does it take for probiotics to start working?

How quickly a probiotic starts working is down to several factors. For instance:

  • your own body
  • the condition you want to support
  • the type of bacteria in the supplement you’re taking
  • The strength (number of bacteria) of the supplement you’re taking

Initial research has attempted to answer this question for the following conditions:


One piece of research that looked at 63 studies on probiotics and acute diarrhea found that some people felt better after two days of taking probiotics (Source: NCBI). Another study of 60 participants with H. pylori (the bacterial infection responsible for stomach ulcers) showed symptoms of antibiotic-related diarrhoea and nausea to improve within 14 days (Source: ONLINE LIBRARY WILEY).


When 70 people with constipation drank a probiotic-rich beverage containing the bacteria Lactobacillus acidophilus, Bifidobacterium animalis lactis, Bifidobacterium longum and Bifidobacterium bifidum for four weeks, most of them reported improvements by the start of the second week (Source: NCBI).

However, research that looked at 47 studies on the effect of probiotics on constipation in children found that despite the probiotics having a positive effect on the gut ‘habitat’, there was no evidence to recommend them in the treatment of paediatric constipation (Source: NCBI).


Studies have shown that probiotics can help with bloating and wind. In one study, it took 21 days before people’s bloating got better (Source: ONLINE LIBRARY WILEY). In another, researchers gave 60 participants probiotics for eight weeks. By week four their bloating had improved, but symptoms continued to get better until eight weeks after they started taking the supplement (Source: NCBI).

Learn more about your gut health. Talk to our experts.


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How do you know if a probiotic is working?

We can’t see inside our bodies, so the only way to know if a probiotic is working or not is to watch our symptoms.

Confusingly, sometimes symptoms can get worse before they get better. Remember that we have about 100 trillion individual bacteria inside our guts, made up of around 1000 different bacterial families, so when we add a new bunch to the mix they might take some time to settle in with the resident population.

Until they do that, you might suffer with a bit of bloating and/or gas. On the other hand, you might not. If you’ve just started taking a probiotic, you might find the following points helpful:

  • Give it around a week for side-effects like extra bloating and gas to settle.
  • You might find your symptoms—like constipation or diarrhoea—temporarily get worse. Again, give your gut about a week to ‘decide’ if that particular probiotic is right for you.
  • Always start with a low dose and work your way up. If the packet recommends two capsules a day, for instance, start with half a capsule and see how you react before building up to the full dose.
  • If the side-effects don’t ease within a week or so, try a different probiotic.

Probiotic foods

A lot of people find that probiotic foods work better for them than supplements like probiotic tablets or powders. You could try

  • Sauerkraut (a fermented cabbage popular in Germany)
  • Kim-chi (a type of fermented cabbage eaten in Korea
  • Kefir (a fermented milk drink)
  • Probiotic yogurt
    Technically all yogurt should be probiotic but many modern supermarket brands aren’t. Make sure your yogurt has been fermented with a live culture.
  • Kombucha (a fermented sweet drink)

It’s important to remember that on the supermarket shelves, a lot of these products aren’t really probiotic foods. For instance, most commercially available sauerkraut is just cabbage in vinegar. The genuine article should list a culture in the ingredients, usually a bacteria from the lactobacillus family that the manufacturers have used to ferment the product, giving it that characteristically sour tang.

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What happens to your body when you start taking probiotics?

When you start taking probiotics, your reaction could be anything from nothing at all to severe bloating, constipation, diarrhoea or nausea. Some people report:

  • insomnia
  • skin rashes
  • anxiety
  • headaches

These reactions usually die down within a week (Source: NCBI).

On the positive side, some people report almost immediate benefits on taking probiotics, which can include:

  • a strengthened immune system
  • reduced cholesterol
  • easing of IBS symptoms
  • lower blood pressure
  • better tolerance of certain foods (Source: NCBI)

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Is it OK to take a probiotic every day?

Most experts agree that it’s fine—even recommended—to take a probiotic every day. However, some researchers claim that probiotics may not be safe at all.

For instance, some believe that probiotics might pose a threat to immunity in vulnerable people and turn into ‘opportunistic pathogens’—bad bugs— that could cause pneumonia, heart infections, and sepsis (Source: SCIENCE DIRECT). However there doesn’t appear to be any evidence to support this claim.

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What are the side effects of too many probiotics?

If you take too many probiotics, you’ll probably suffer with bloating, gas, and possibly diarrhoea. There are currently no maximum RDAs (recommended daily allowances) for any probiotic strains, as they aren’t considered a vital part of your diet by any health authority.

However, research findings generally suggest anything from 1 billion CFU (colony forming units: the term specialists use to describe the number of microorganisms present in the product) to 10 billion CFU as an effective daily dose, depending on the strain (Source: NCBI).

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How long should you take probiotics?

A lot of research suggests that probiotics don’t ‘colonise’ the gut, so we need to take them every day.

Twelve volunteers in a study were given either a probiotic mixture or placebo to investigate the ability of five Lactobacilli strains to colonise in humans (Source: NCBI).

Most of the strains were still in the guts of the participants 18 days after they took the probiotic, but by day 23, only two strains were present, and by day 29 there was no evidence of any of the strains.

So if you find the positive effects of your probiotics wear off when you stop taking them, keep taking them! There’s currently no evidence to suggest this is a bad idea.

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Key takeaways

There’s a lot of evidence to back up the use of probiotics for many conditions, including IBS, food intolerances, diarrhoea, constipation and bloating.

However, because people respond so differently to the same probiotic products, it’s impossible to say that any of them will definitely help you.

Lactobacillus acidophilus, Streptococcus thermophilus, Bifidobacterium breve and Bifidobacterium longum have the most weight of evidence behind them for IBS.

If you want to try probiotics, start slowly to avoid any side-effects.

It’s possible your symptoms might get worse before they get better: give it a week to decide if a probiotic is right for you.

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Alexandra Falconer MA (Dist) DipCNM mBANT is a Registered Nutritional Therapist specialising in IBS and related conditions. A graduate of Brighton’s College of Naturopathic Medicine, she is committed to fighting the root causes of chronic illness and bringing functional medicine to everyone who needs it.

Before her natural health career, Alex was a journalist and copywriter. She continues to write for magazines and media agencies, and now combines her two great passions—writing and health—by creating content that empowers people to claim their right to a healthy body and mind.
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