What is Acidophilus?

Acidophilus is a species of good bacteria within the Lactobacillus genus. There are many different strains (types) within this species, including Lactobacillus acidophilus NCFM®. Find out everything you need to know about this important species of friendly bacteria and its benefits in this FAQ.

Acidophilus taxonomy diagram
Taxonomy diagram

What is 'acidophilus'?

Many people are confused by the difference between 'acidophilus' and friendly bacteria; in fact, many people just ask for an 'acidophilus supplement' when choosing live cultures. But L. acidophilus is just one of many different species of good bacteria from the genus Lactobacillus. It is found in the gut, mouth and vagina, as well as in various fermented foods such as yoghurt and sauerkraut. Its full name is written as Lactobacillus acidophilus. Healthcare practitioners can find out more about L. acidophilus on the Probiotics Database, on the Probiotic Professionals site.

What is even more important to understand is that within each species of bacteria, including the L. acidophilus ‘species’, there are a large number of specific ‘strains’ (types), each with unique properties. Strains from the Lactobacillus genus tend to be the most widely used in live cultures supplements due to their versatile nature. But strains within any species of friendly bacteria will have unique properties, so when choosing live cultures supplements it is important to compare them at strain level, as opposed to merely species or genus level. 

  • Key takeaway: L. acidophilus is a species of bacteria from the Lactobacillus genus, typically found in the body, in natural foods, and in supplements. Within each friendly bacteria species, there are many different individual ‘strains’. Read more about the difference between species and strains.

One very important strain from this species is Lactobacillus acidophilus NCFM®. It's one of the most widely researched strains of bacteria in the world, and certainly the most extensively researched strain of this species. The Optibac range contains a large selection of highly researched L. acidophilus strains, including Lactobacillus acidophilus NCFM® which can be found in the following Optibac supplements:

Other Optibac Lactobacillus acidophilus strains include Rosell-52 which can be found in these products:

Lactobacillus acidophilus La-05® and Lactobacillus acidophilus La-14® can be found in this Optibac supplement:


Acidophilus under microscope
L. acidophilus under microscope

What is L. acidophilus used for?

This species is so-called because it is made up of lactic acid-producing bacteria. Due to their versatility and ability to colonise in many areas of the body, they have been researched for numerous different health conditions. But one shared preference for all these strains is to use carbohydrates and sugars such as lactose as a fermentation substrate. This means that they break down and use these sugars as 'food' when they pass through our intestine.

This is why they are often used by those with lactose intolerances1. People with lactose intolerance lack sufficient digestive enzymes to digest lactose (a sugar found in milk and dairy products) but strains of L. acidophilus bacteria can help to break lactose down into a more digestible form as they produce lactic and acetic acids as a by-product of fermentation. These acids lower the pH of the intestines, discouraging the over-growth of bad bacteria, known as pathogens, and encouraging the growth of ‘good’ or ‘friendly’ bacteria in the gut. Consequently one L. acidophilus benefit is in maintaining a healthy balance of gut flora.

Beyond these characteristics, which are common to all bacteria within this species, most of the known benefits of L. acidophilus are found at ‘strain’ level.For example, the Lactobacillus acidophilus NCFM® strain has very different characteristics and health benefits to the Lactobacillus acidophilus La-14® strain.

  • Key takeaway: When choosing the best acidophilus supplement for your needs, look at the L. acidophilus strains which have been researched for the specific health condition or symptom you wish to support. 

What is the best L. acidophilus friendly bacteria?

This really depends on what is meant by ‘best’! In general, it's 'best' to find the right strain to suit you and your own specific health requirements, which can involve some research. 

Live cultures also come in different ‘formats’: you can choose from acidophilus powders, acidophilus tablets, acidophilus capsules and even acidophilus in liquid format. It's best to choose a format which you will find easy to take, as otherwise you might give up taking them. The majority of products on the market are in capsule format, as these are generally found to be easier to swallow than tablets. Capsules and powders in sachets tend to have better shelf-stability and lower risk of contamination than loose powders or liquids.

Some manufacturers of live cultures use enterically coated capsules to protect the bacteria from the harsh stomach acid. Optibac use robust strains of friendly bacteria that survive to reach the gut without enteric coating. This means our capsules can be opened, and the contents sprinkled on to cool, non-acidic food or drinks, and you can still be sure that the bacteria will survive and you are getting the full dose2. You may like to read the following FAQ: Can I open live cultures capsules?

Here are some top tips to look for in your chosen supplement:

  • Choose a strain with sufficient scientific evidence to support its safety and ability to survive in the gut.
  • Opt for ‘quality over quantity’. Don’t be drawn in solely by huge billion counts of a supplement. Higher billions do not necessarily equal higher product quality – it’s much more important to get the most researched strains, even if they’re in lower quantities. It’s definitely a case of ‘quality over quantity’ when it comes to friendly bacteria supplements.
  • Look at the areas and groups of people in which the strains have been researched, and choose strains which seem most appropriate for you.
  • Check the product has a 'time of expiry' guarantee as opposed to a 'time of manufacture' guarantee, as this means the product strength is guaranteed until the supplement goes out of date, rather than just at the time of manufacture (as numbers decrease after this point).
  • Make sure your supplement is easy to take. If you choose highly researched live cultures in capsules or tablets then they won't need the protection of the capsule, and you'll be able to chew them or open them and take the contents alone if that's easier for you. 

Highly researched strains such as Lactobacillus acidophilus NCFM®, which can be found in our supplements Every Day EXTRA and Every Day MAX, will satisfy all of the above mentioned product quality criteria2.

  • Key takeaway: Do your homework before buying an L. acidophilus supplement. Choose one containing high quality, well-researched strains which meet your own individual health needs, whilst also satisfying the above quality criteria, and choose a format which you will find easy to take. For more information, read How to Choose the Best Friendly Bacteria Supplements

How much Lactobacillus acidophilus should I take?

This question is a little tricky to answer, as different health symptoms may require not only different strains of good bacteria, but potentially different strengths. As a general rule it's best to follow the clinical trial data, and take around the same number of billions that were used in the clinical trials using the strains. Wherever possible Optibac supplements are formulated in this way, using data and dosage information from the most significant clinical trials. But everyone has a unique gut microbiome, and higher or lower strengths suit different people. You may need to try a couple of different supplements before finding the one which suits you best, though allow a week or two for the microbiome to adjust when you first start to take a new supplement.

  • Key takeaway: Different conditions may require different strengths of friendly bacteria, where possible take a similar CFU (billions) count to that used in clinical trials relating to your specific health condition. Experiment until you find the strength that suits you best.

Is it OK to take L. acidophilus every day?

This is a common concern, but people from all cultures have been consuming live cultures daily in a variety of fermented foods and drinks for hundreds of years. In the majority of research studies using live cultures, participants are typically given a daily intake of friendly bacteria3. Some supplements, such as One Week Flat, are designed to be taken as a short course as and when desired, but many people find they get on better when they take a friendly bacteria supplement every day. There's no evidence that doing this will cause dependency or 'overdose', and daily consumption of good bacteria is generally considered to be of benefit.

  • Key takeaway: It's fine, and often desirable, to take your favourite friendly bacteria every day. Read more about taking good bacteria every day over on the Probiotics Learning Lab.

Are there any side effects from taking L. acidophilus?

In general live cultures, including those from the L.acidophilus species, are considered to be extremely safe4 and have very few side effects. The majority of people do not experience any negative symptoms from taking live cultures supplements. However, everybody is different, and therefore everyone reacts to things differently. When first taking a new live cultures supplement, some people may initially experience mild digestive symptoms, such as bloating or excess gas. In most cases these symptoms do not last for longer than a few days; they are simply the result of changes in the bacterial populations in the gut. So some mild digestive effects can simply be a sign that changes are taking place within the eco-system of their gut.

Whilst these may be bothersome, they can be a positive sign that the ‘friendly’ bacteria are doing their ‘job’, crowding out pathogenic strains of bacteria and competing for space on the gut wall lining. However, if any side effect is troubling you, or lasts for longer than described, stop taking the product and contact the manufacturer for advice. It could be other ingredients in the product that are causing issues, such as prebiotic fibres. Or, it could just be that the strain of acidophilus is not compatible with your individual microbiome at that time. Always listen to your own body, and respect its uniqueness.

Any concerning symptoms should always be discussed with a doctor, rather than assuming they are related to a natural supplement.

  • Key takeaway: Side effects from live cultures are very unusual.  They may occasionally cause mild abdominal discomfort and/or bloating in some people, but this is typically short-term and indicates that the bacteria are reaching the gut. If symptoms persist speak to the manufacturer for advice. Read our FAQ ‘Do live cultures have side effects?’ to find out more.

Who should not take L. acidophilus?

As we've learned so far, live cultures are very safe to be taken daily by the majority of people, from birth into old age. They are found naturally in our bodies, in fermented foods, and also in the environment. After decades of research, they are generally considered to be a positive addition to our diet. However, as with any natural supplement, those people who are suffering with a serious health condition or who are taking regular medication should always consult with their doctor before taking natural supplements. 

  • Key takeaway: Live cultures are very safe for most people to take; however, individuals with serious medical conditions or taking medications should speak to their doctor before taking natural supplements. Visit the Probiotics Learning Lab for more information about who should not take live cultures.

How long does L. acidophilus take to work?

This is a question that everyone wants to know the answer to, but frustratingly there is no ‘one size fits all’ answer here either! With everyone’s microbiome being as unique to them as their fingerprint, it is impossible to know for certain how long it will take to feel the benefits of taking these friendly bacteria supplements.

We receive wonderful feedback and product reviews from our customers. For some people our supplements have an almost instant effect, whereas for others it can take several weeks or more. It depends partly on the state of a persons’ health to start with and also their compliance with taking the product. Diet, lifestyle and any medications being taken are other factors to consider. In general, I would advise patience. The benefits are well worth it, and your health will thank you for it in the longer term.

  • Key takeaway: Everybody responds differently, and at different speeds, when starting a new live cultures supplement. Don’t be disappointed if results take a little while, they will be worth it in the longer term.

You should now be fully informed about all aspects of L. acidophilus, so can go ahead and shop for your ideal acidophilus now!

You may also like to read the following article:

What is Lactobacillus?

For further research in to L.acidophilus and specific strains within this species healthcare professionals might like to take a look at The Probiotics Database.

Authors: Dr Aisling Dwyer MB BCh BAO (Medicine, Surgery and Obstetrics), MSc (Personalised Nutrition)​, Dr Kate Stephens PhD Food and Microbial Sciences; Gut Microbiology (University of Reading), BSc Medical Microbiology


  1. Montes, R.G. et al., (1995). ‘Effect of Milks Inoculated with Lactobacillus acidophilus or a Yogurt Starter Culture in Lactose-Maldigesting Children’. Journal of Dairy Science. 78(8): 1657 – 1664.
  2. Mai, V., et al. (2017) ‘Novel encapsulation improves recovery of probiotic strains in fecal samples of human volunteers’. Appl Microbiol Biotechnol, 101(4):1419-1425.
  3. Iannitti, T. and Palmieri, B. (2010). Therapeutical use of probiotic formulations in clinical practice. Clinical Nutrition, 29(6): 701-725.
  4. Morovic, W., et al. (2017) ‘Safety evaluation of HOWARU® Restore (Lactobacillus acidophilus NCFM®, Lactobacillus paracasei Lpc-37, Bifidobacterium animalis subsp. lactis Bl-04 and B. lactis Bi-07) for antibiotic resistance, genomic risk factors, and acute toxicity’. Food Chem Toxicol, 110:316-324.