Antibiotics are lifesavers. Since their discovery, diseases and infections that used to be considered untreatable are a thing of the past, and with the research and development that’s gone into them ever since, today they are a key player in modern medicine.
But are they all good? What about side effects? Can they have unintended knock on effects?
The truth is that whilst antibiotics are very important, they don’t come without side effects. Most antibiotics are broad spectrum, which means they don’t just kill one specific strain of bacteria, but a variety of them. Sometimes it’s one family of bacteria, sometimes it’s a variety of different families, sometimes it can affect hundreds of different species. This can be great for dealing with very serious infections, but it means that a lot of the time some of the good guys get caught in the crossfire, and the beneficial microbes in your body can become accidental casualties. Since most antibiotics are commonly taken orally as pills, they absorb through your gut, and so it’s your gut that bears the brunt of these side effects.
The side effects can vary, with the milder side of the spectrum seeing people dealing with bloating, gut discomfort or maybe a little extra wind. On the more severe end though we see people developing AAD, or Antibiotic Associated Diarrhoea, which can go on for days and present many issues of its own, not to mention being very unpleasant!
We’ve already covered in our other articles how BB12 and LGG have both been studied for their potential to help keep AAD under control. They’ve both shown consistently very positive results in this area! But this article is going to focus on just the antibiotics themselves. How do they affect your gut, really? What’s the science, and what does it say? There’s been a lot of research into this area, so let’s take a look at what was found, and what we can do about it.
Show me the science
There have been a lot of studies into this area, and we could talk all day about the findings. But let’s focus in on some of the effects that were found across multiple studies, and what they mean for you. All of these studies were randomised control trials, the gold standard in clinical testing, so you know they produce fair results that we can trust.
Reduced Diversity
One of the main areas of testing in this area is the diversity of bacteria still alive in the gut after a course of antibiotics. Some studies looked at adults, some at toddlers, some in just the short term straight after the course was finished, but some in the long term too, and a consistent pattern emerges.
One study found a significant drop in healthy adults’ gut diversity a full 4 months after taking only one course of antibiotics! Another in toddlers showed similar results, with a severe drop in both diversity and richness, although when tested at least 1 year later their little guts had fully recovered.
Other studies showed similar results. One study in 450 children kept the same pattern, the diversity was significantly decreased 2 weeks after antibiotics, with the gut recovering to normal when tested 6 months later.
This was all confirmed by a major meta-analysis. This is a type of study that takes the results of other high-quality studies and looks for a pattern across the board. They found the same result, that the studies show diversity drops very significantly with antibiotics. One study even found changes in 157 different types of bacteria after antibiotics! So, the effect can be widespread.
It’s important to remember that these studies looked at different kinds of antibiotic, in different people of different ages. Some antibiotics had very few negative effects, some packed a real punch to the gut microbiome. But the picture is clear, the microbiome can suffer during a course of antibiotics, and can take months to rebuild on its own.
Richness
Another factor often tested in these studies is the ‘richness’ of the gut bacteria, in other words, not just testing what’s in there but how much of it there is too, an important thing to think about when taking antibiotics.
Studies in this area show pretty consistent results. The study in toddlers found an approximately 23% drop in richness, a very significant reduction. Not only that, but when they looked at specific bacteria the picture got a little clearer. They found that Bifidobacterium (the same family of bacteria as BB12) had been hit the hardest, with a drop of approximately 50x!!
This reinforces the results around diversity. If there are some bacteria left, they can rebuild, which is why the gut returns to normal eventually. But the harder they’re hit, the longer it’ll take them, and if a longer course of antibiotics is used their numbers will be hit a lot harder.
Knock on effects
One very interesting study in this area didn’t just ask what happened to the bacteria, but what happens to the body as a result of the drop in numbers? They did this by having a look at the levels short chain fatty acids in the gut after antibiotics in a group of prediabetic men, so a more vulnerable group of people than healthy adults.
SCFAs are group of chemicals that your gut microbes produce as they break down food, and are very important for human health. They’ve been studied a lot themselves, and have been linked to keeping inflammation down, a strong gut barrier and lining, gut regularity and even effects on the gut brain connection. So, they’re very important, and a good marker of a healthy gut!
The study found that after one kind of antibiotic the levels of SCFAs in the guts of the participants dropped dramatically after a 7 day course. This helps us fill in the gaps as it shows that by hitting the microbes in the gut, those microbes weren’t around to produce the good things they do for us. As a result a 7 day course of antibiotics could lead to knock on effects in other areas of the body too!
So, what do we do about it? It’s not all doom and gloom!
It’s important to remember that while there are side effects from antibiotics, they’re still very important lifesaving drugs. This isn’t about replacing them, we need them in modern medicine, but instead about looking at how we can reduce their side effects, and work with them to keep the impact down whilst still using them to save lives.
One area that’s received a lot of study here is probiotics. Scientists said: if we’re killing good bacteria too then what if we send in more good bacteria alongside the antibiotics? It makes sense when you think about it.
We won’t go into too much detail here, but the upshot is, it worked! Many studies have shown a course of probiotics alongside the antibiotics helped to significantly reduce AAD symptoms, as well as reducing the time it took for people to recover. Two of the most studied bacteria in this area are the ones we use at BetterGuts, LGG and BB12. We have articles on both of them for their effects on antibiotic side effects, so check out our learn hub to see the evidence and learn what these microbes can do!
This has been recognised by a variety of international bodies as well. The European/British Society for Paediatric Hepatology, Gastroenterology and Nutrition have both recommended probiotics alongside antibiotics. The Australian GP handbook addresses it too with advice for GPs, and it’s been recognised by both Health Canada and the British Dietetic Association as an area with promising evidence.
Even without probiotics, studies show that the gut will return to normal with enough time, but a recovery of a few months can feel a lot longer than it is. It’s important to ask your doctor if you’re thinking about taking supplements alongside any existing medication, but if you get put on a course of antibiotics, especially a long course, it could be worth considering that a good probiotic supplement backed by science might help you along the way!
References (the science) – Don’t just take our word for it:
- Zaura E, Brandt BW, Teixeira de Mattos MJ, Buijs MJ, Caspers MPM, Rashid MU, Weintraub A, Nord CE, Savell A, Hu Y, Coates AR, Hubank M, Spratt DA, Wilson M, Keijser. BJF, Crielaard W. 2015. Same exposure but two radically different responses to antibiotics: resilience of the salivary microbiome versus long-term microbial shifts in feces. mBio 6(6):e01693-15. doi:10.1128/mBio.01693-15.
- Wei S, Mortensen MS, Stokholm J, Brejnrod AD, Thorsen J, Rasmussen MA, Trivedi U, Bisgaard H, Sørensen SJ. Short- and long-term impacts of azithromycin treatment on the gut microbiota in children: A double-blind, randomized, placebo-controlled trial. EBioMedicine. 2018 Dec;38:265-272. doi: 10.1016/j.ebiom.2018.11.035. Epub 2018 Nov 23. PMID: 30478001; PMCID: PMC6306380.
- Doan T, Liu Z, Sié A, Dah C, Bountogo M, Ouattara M, Coulibaly B, Kiemde D, Zonou G, Nebie E, Brogdon J, Lebas E, Hinterwirth A, Zhong L, Chen C, Zhou Z, Porco T, Arnold BF, Oldenburg CE, Lietman TM. Gut Microbiome Diversity and Antimicrobial Resistance After a Single Dose of Oral Azithromycin in Children: A Randomized Placebo-Controlled Trial. Am J Trop Med Hyg. 2024 Jan 16;110(2):291-294. doi: 10.4269/ajtmh.23-0651. PMID: 38227963; PMCID: PMC10859792.
- Reijnders, D., Goossens, G. H., Hermes, G. D. A., Neis, E. P. J. G., van der Beek, C. M., Most, J., Holst, J. J., Lenaerts, K., Kootte, R. S., Nieuwdorp, M., Groen, A. K., Damink, S. W. M. O., Boekschoten, M. V., Smidt, H., Zoetendal, E. G., Dejong, C. H. C., & Blaak, E. E. (2016). Effects of Gut Microbiota Manipulation by Antibiotics on Host Metabolism in Obese Humans: A Randomized Double-Blind Placebo-Controlled Trial. Cell Metabolism, 24(1), 63-74. https://doi.org/10.1016/j.cmet.2016.06.016
- McDonnell L, Gilkes A, Ashworth M, Rowland V, Harries TH, Armstrong D, White P. Association between antibiotics and gut microbiome dysbiosis in children: systematic review and meta-analysis. Gut Microbes. 2021 Jan-Dec;13(1):1-18. doi: 10.1080/19490976.2020.1870402. PMID: 33651651; PMCID: PMC7928022.
