Do Antibiotics Make You Gain Weight?

Written by

Jessica Guht

Jessica is a medical writer with an unquenched thirst to discover something new. She believes that medical content should be accessible to everyone and strives to write content that every single person can understand. When Jessica isn’t writing, she can usually be found reading a book with a dog cuddled in her lap. Jessica has a Masters of Engineering degree in Biomedical Engineering.

Medically reviewed by

Amy Dougherty, FNP-BC, AGAC

Amy is a Board Certified Family Health Nurse Practitioner (FNP) with over 15 years of experience working in Hospital Medicine, Urgent Care and Primary Care practices. Amy graduated Thomas Jefferson University with high distinction earning a Bachelor of Science in Nursing in 2008, a Master of Science in Nursing in 2010 and a Post Master's Certificate in Adult Gerontology Acute Care (AGAC) in 2014. She was recognized by the Elite American Nurses Association in 2013 for her dedication, achievements and leadership in the field Nursing. She served as a clinical preceptor for a number of Nurse Practitioner students and enjoys teaching the bright minds of future NPs.

When it comes to bacterial infections, antibiotics are the number one treatment. They help to kill or interfere with the bacteria’s growth, aiding your immune system as it fights the infection. 

However, there are side effects associated with antibiotics, such as bloating and an upset stomach. These issues affecting the gastrointestinal system may make you wonder if antibiotics can also make you gain weight, and while weight gain because of antibiotics is possible, it does not always happen.

Continue reading to learn more about antibiotics, how they affect your gut microbiome, and how this may result in weight gain. 

Table of Contents

• About Antibiotics
• Can Antibiotics Make You Gain Weight?
• Do Antibiotics Cause Bloating?
• Do Antibiotics Make You Hungry and Increase Your Appetite?
• When to See a Doctor?
• Key Takeaways

About Antibiotics

Antibiotics are one of the most commonly prescribed medications, and their purpose is to treat bacterial infections. They accomplish this by killing bacteria directly or keeping them from growing and/or multiplying. No matter their mechanism of action, the result is the eradication of your infection. 

Antibiotics can come in many forms, including pills, topical creams, liquid suspensions, eye drops, and even IV infusions for more severe infections. Not only that, but there are hundreds of different types of antibiotics, each with their own mechanism of action and bacteria they are effective against. 

Some illnesses which may require antibiotics include:

• urinary tract infections (UTIs)
• strep throat
• E. coli
• acne
• bronchitis
• sexually transmitted diseases (STDs)
• skin infections
• upper respiratory tract infection
• ear infection
• conjunctivitis (pink eye)
• eye infections
• gum disease
• meningitis

Of note, some of these illnesses may also be caused by a virus, but antibiotics will only be effective if the cause is bacterial. 

While each antibiotic has its own set of side effects, some of the most common have to do with an upset stomach, such as stomach pain, nausea, and diarrhea. This is likely because antibiotics, as is their nature, attack the bacteria in the body, but this can also include the good bacteria in the stomach. This can then lead to problems with the gut, manifesting as stomach pain and digestive issues. 

Can Antibiotics Make You Gain Weight?

There are many reasons why the question of whether antibiotics can make you gain weight cannot be answered with a simple yes or no. For one, there are hundreds of antibiotics, each affecting different bacteria, meaning some may affect the bacteria in your gut more than others. Additionally, everyone is different, so what may make one person gain weight will have no effect on the other. 

Beyond these criteria, research also shows that there is no definitive answer. Antibiotics may make you gain weight, but they also may not. Let’s look at some studies and how scientists speculate that antibiotics can cause weight gain in some people. 

They Can Alter Your Gut Bacteria

One way that antibiotics may cause weight gain has to do with their effect on your microbiota or the bacteria in your body. The gut is the most well-known microbiome, and it contains trillions of bacteria that help with everything from the immune system to breaking down and digesting food. There are many bacteria in there, and they’re all important. 

However, the role of antibiotics is to kill bacteria, which also applies to the good bacteria in your gut. Not only can this occur when you take a short course of antibiotics, but the consequences can be even more drastic for those taking antibiotics repeatedly. Research has shown that frequent antibiotic use can change the microbiota forever and affect how it breaks down food. In particular, it makes it so that the nutrients absorbed have a higher calorie count, and a higher calorie count can then lead to weight gain. 

This was proven in a study on children finding that, by 15, children who had taken antibiotics seven or more times during their childhood weighed an additional three pounds compared to kids who had taken no antibiotics. 

Now, the weight gain observed in this study is undeniably minimal, but the authors suggest that these findings raise the possibility that these effects could compound into adulthood. 

Other studies have seen similar results, such as a study on mice that found antibiotic exposure caused mice to gain more weight than other mice on the same diet. 

They Can Influence Hormone Production

Research has also shown that antibiotics may also affect your hormones, namely the hormone called ghrelin, the body’s hunger hormone. This hormone is primarily secreted in the stomach lining and tells your brain through signals when it wants to eat. The higher your ghrelin levels, the hungrier you feel and the more likely you are to overeat. 

A study on energy hormones in those taking antibiotics found that ghrelin levels were almost six times higher than before antibiotics were started, meaning these individuals are much more likely to eat more than their body needs simply because their hormones send signals to the brain that they are hungry. 

Do Antibiotics Cause Bloating?

Antibiotics can wipe out up to one-third of the bacteria in your gut, which can cause some severe disturbances. In addition to increasing acidity and discomfort, it can also result in bloating. 

However, you can help to manage these digestive issues by staying hydrated. 

Do Antibiotics Make You Hungry and Increase Your Appetite?

Antibiotics can make you hungry, and this is because of their influence on the hormone ghrelin. This hormone is primarily secreted by cells in the stomach lining, and as the body’s hunger hormone, it tells your brain that it wants to eat, increasing your appetite. 

Antibiotics have been shown to increase ghrelin levels, which then makes you feel hungrier and can make you eat more. 

When to See a Doctor?

If you feel sick, it is always best to see a doctor. Depending on your symptoms, they may determine that an antibiotic is the best course of treatment. 

If you take an antibiotic for a short-term infection, there is minimal need to worry about weight gain, as you are likely to take the antibiotic for only a few days or weeks. Once you discontinue it, your body’s gut microbiome and hormone levels will steadily return to normal. 

However, those taking longer-term antibiotics, such as those taking them for hormonal acne, may want to speak to their doctor if there are any noticeable weight changes, especially since this can have life-long consequences. 

If you are gaining unexplained weight while on antibiotics, contact your doctor about an alternative treatment plan or lifestyle changes you can make to live a healthier life. 

For a quick and convenient way to meet with a doctor, try DrHouse. With our app, you can meet with a board-certified professional in just 15 minutes to discuss any concerning symptoms you may have while on antibiotics, such as weight gain or bloating, and come to a solution. 

Key Takeaways

Antibiotics are a medication commonly prescribed to treat bacterial infections. However, there are some side effects with antibiotics, most of which are related to the antibiotic’s disturbance of your gut bacteria. 

Not all bacteria are harmful, but antibiotics, unfortunately, cannot differentiate, which is how they can also end up attacking the good bacteria in your gut. In addition to aiding the immune system, this bacteria plays a significant role in your digestive system. When the bacteria levels are disturbed, it can affect how the microbiota breaks down food or even increase ghrelin levels. Both of these consequences can lead to weight gain. 

If you are taking an antibiotic long-term and notice weight gain that is otherwise unexplained, reach out to your doctor for advice on stopping your weight gain. 

Sources:

• Patangia, D., Anthony Ryan, C., Dempsey, E., Paul Ross, R., & Stanton, C. (2022). Impact of antibiotics on the human microbiome and consequences for host health. Microbiologyopen, 11(1). doi: https://www.doi.org/10.1002/mbo3.1260 
• Schwartz, B. S., Pollak, J., Bailey-Davis, L., Hirsch, A. G., Cosgrove, S. E., Nau, C., Kress, A. M., Glass, T. A., & Bandeen-Roche, K. (2016). Antibiotic use and childhood body mass index trajectory. International journal of obesity (2005), 40(4), 615–621. https://doi.org/10.1038/ijo.2015.218 
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• Francois, F., Roper, J., Joseph, N., Pei, Z., Chhada, A., & Shak, J. et al. (2011). The effect of H. pylori eradication on meal-associated changes in plasma ghrelin and leptin. BMC Gastroenterology, 11(1). doi: https://www.doi.org/10.1186/1471-230x-11-37 
• Patel P, Wermuth HR, Calhoun C, et al. Antibiotics. [Updated 2023 May 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535443/ 
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