Mixing Sweeteners and Antidepressants Could Be Quietly Altering Your Microbiome

Low-calorie sweeteners are often thought to pass through our bodies completely unnoticed, but new research suggests they are far more biologically active than previously thought.

Researchers at the Medical Research Council (MRC) Toxicology Unit at the University of Cambridge recently discovered that 75% of the commercial sweeteners they tested directly altered the growth of human gut microbes.

The study, published in Molecular Systems Biology, found that when the sugar substitutes were mixed with common medications such as antidepressants, they impacted gut diversity and impaired essential metabolic functions.

Sweeteners and the gut microbiome

Many people choose low-calorie sweeteners to cut down on sugar, believing these substitutes are somewhat “healthier” for our bodies.

However, evidence has linked these additives to metabolic conditions such as obesity and type 2 diabetes. This link has driven scientists to investigate how these sugar substitutes behave once they reach our digestive systems.

Although it is widely accepted that the gut microbiome is necessary for health, researchers don’t yet understand how sweeteners may be affecting our resident microbes.

“Most of what we know about the potential impact of sweeteners on our health comes from animal research or from population studies. While these studies have indicated involvement of the microbiome in mediating the effect of sweeteners, it’s difficult to know how sweeteners act in the body—is it through direct interactions with our gut bacteria?” said corresponding author Prof. Kiran Patil, from the MRC Toxicology Unit at the University of Cambridge.

“Answering this is further complicated by the fact that we rarely ever take sweeteners by themselves—we take them with drinks, in snacks, or even in medication to mask bitterness,” added lead author Dr. Sonja Blasche, a senior research associate at the MRC Toxicology Unit.

To solve this, Blasche, Patil, and the team mapped the impact of commercial sweeteners on 25 human gut bacterial strains in laboratory cultures.

How sweetener and medication combinations damage the gut microbiome

The researchers exposed the bacterial cultures to 39 sweeteners at a concentration of 50 µM, which mirrors levels in the human colon.

The team also wanted to see how combining sweeteners with common additives or medications affected the survival of these gut microbes.

They tested 156 combinations of sweeteners with substances such as caffeine, flavorings, and the antidepressant duloxetine. They also grew a synthetic community of all 25 species together over five generations to study group dynamics.

Around 75% of the sweeteners altered the growth of at least one bacterial strain, with isosteviol—a compound derived from stevia—acting as the strongest inhibitor. Some of the sweeteners slowed, or completely stopped, the growth of beneficial bacterial strains.

The team also discovered over 100 chemical interactions when the sweeteners were combined with other substances, resulting in them acting differently compared to when they were grown alone. Of these, 34 combinations strengthened the inhibitory effects, while 68 weakened them.

In particular, the isosteviol-duloxetine mix suppressed two beneficial gut bacteria: Roseburia intestinalis (R. intestinalis) and Parabacteroides merdae.

In the mixed community, this combination also reduced microbial diversity. By analyzing bacterial proteins and genes, the researchers found that the surviving bacteria relied on cell walls and magnesium transport systems to withstand the pairing. The mixture also disrupted bacterial metabolism, causing a 50% spike in glutamine secretion while cutting protective butyric acid by over 25% in R. intestinalis.

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The real-world health effects of an altered gut microbiome

“Sweeteners are often marketed as metabolically neutral, but our study challenges this idea. We found that they can directly affect gut bacteria, particularly when mixed with other compounds such as medication and food additives. These common combinations could have unintended effects on our gut microbiome,” said Blasche.

The metabolic shifts caused by the isosteviol-duloxetine mixture had direct consequences: the fluid from the bacterial cultures proved toxic to human HeLa cells. The drop in protective short-chain fatty acids, including butyrate and propionate, also damaged gut cell stability, triggering a reduction of over 75% in important immune-signaling proteins.

However, it is important to note that the experiments were conducted in vitro using a simplified 25-strain community at a fixed concentration; the human gut is far more complex and variable.

Future research is needed to track these chemical interactions in human trials.

“Our study suggests that artificial sweeteners don’t just pass through the body passively—they can interact with gut microbes, and these effects can be amplified or altered by other substances like medications. These findings can help guide new studies towards understanding how sweeteners might influence health in unexpected ways,” concluded Patil.

Reference: Blasche S, Periwal V, Beristain Covarrubias N, et al. Common xenobiotics modulate gut microbial responses to low‑calorie sweeteners in vitro. Mol Syst Biol. doi: 10.1038/s44320-026-00225-6

This article is a rework of a press release issued by the University of Cambridge. Material has been edited for length and content.