Probiotic supplements containing more than one strain of live bacteria are often referred to as 'multi-strain' supplements, or sometimes as 'poly-strain' or 'polybiotics'.

Generally speaking, a multi-strain probiotic (see Probiotics Learning Lab) is most suitable as an every day supplement to support gut health. Most high-quality, multi-strain probiotics contain around 5 or 6 different strains, so why not have 10 or 15? In theory, the more strains the better, right?

Well actually, not necessarily. In practice having 10-20 different strains in one supplement carries uncertainties. When it comes to probiotics, the question of survival is an important one, and when one product contains many strains, it is difficult to establish whether all of the strains will survive until the time of consumption. If you are considering stocking a probiotic supplement with a large number of different strains, make sure tests have been conducted to ensure the strains all survive together at the stated billions count until expiry.

If we look at some of the world's leading and most trusted probiotic manufacturers, like the Institut Rosell, these supplements rarely offer more than 6 different probiotic strains per capsule. The Institut Rosell conducts rigorous tests on our 'For every day' to ensure the 6 different strains survive in the capsule at the billions count stated on the pack until the end of the expiry. This is true for the entire range. We cannot speak for other probiotic companies but we understand that it is extremely difficult to find numerous strains that survive together in one capsule and tests proving the survival of 10+ strains in one supplement would be incredibly difficult to achieve. We would be very impressed to see these results!

To find out more about some of the tests we carry out and to see some of the results you may be interested to read nutritional therapist Joanna's blogpost about probiotic claims.

S. Boulardii
S. boulardii is best known for its potential to relieve diarrhoea symptoms

What does the research say?

Dr Lynne McFarland from the University of Seattle has over 150 peer-reviews to her name and has concluded current data shows that adding more strains doesn't always lead to better outcomes for all illnesses1. But she also acknowledges that 'the benefits of multi-strain mixtures may include broader range of effects and more mechanisms of action...' There are clearly pros and cons for single and multi-strain probiotics - the former more stable, the latter has the potential to be more effective, dependent on the strains used and condition being targeted.
For Helicobacter pylori, for example, a single strain leads to a 0.66 day reduction in diarrhoea, whilst a two-strain mix leads to a 0.41 day reduction. In this instance, the single strain has been more effective but importantly, 'these are both significant reductions'. And whilst there is no definitive answer it is clear that more research is needed. Some of the most popular probiotic strains on the market only contain one strain. These are known as 'single-strain probiotics'. Saccharomyces boulardii (S. boulardii) on its own, for example, can be a great option for supporting people with IBS-D. In fact, a study2 published in 2010 found that when treating diarrhoea, associated with rotavirus in children, S. boulardii reduced the duration of the virus and the duration of the fever more effectively than did a mixed probiotic containing both S. boulardii along with L. acidophilus, L. rhamnosus and B. longum strains. It is worth noting, however, that the multi-strain product was more effective at preventing vomiting associated with the virus.

Specific strains for specific conditions

Many multi-strain supplements are formulated to target specific health conditions. Each strain will be selected based on scientific studies and clinical trials, to ensure quality supplements tailored to specific needs. As such, individuals must find the right probiotic for them, as opposed to taking 'any old acidophilus'. Instead of asking 'Am I getting enough strains?', consider 'Am I taking the right strains for me?'. If you are interested you can read more about strain-specificity and its importance, over in the Probiotics Learning Lab.

As you can see there are no hard and fast rules - for some individuals taking a single strain probiotic like Saccharomyces boulardii can suffice, whilst for others a multi-strain probiotic might represent a better option. The quality of the probiotics strains used is by far the most important factor to consider when selecting a supplement that is right for you and looking at the available clinical trials behind the strains will help you to select the right strain (or strains) for your specific health condition or symptom.

For further reading on the topic, take a look at 'The Numbers Myth', over in the Probiotics Learning Lab.


1. Scattergood, G. (2017). 'Multi-strain versus single strain probiotics: More doesn’t necessarily mean better outcomes'. Published online. Available at:

2. Grandy, G et al. (2010) Probiotics in the treatment of acute rotavirus diarrhoea. A randomized, double-blind, controlled trial using two different probiotic preparations in Bolivian children. BMC Infect Dis, 10: 253