Does Drinking Kefir Have Side Effects? What to Know Before You Start

October 7, 2025 •

4 min read

While most healthy people tolerate it well, drinking kefir can lead to temporary side effects like gas and bloating, especially for those new to probiotics. As a fermented food packed with a diverse range of beneficial bacteria and yeast, the gut often needs a period of adjustment.

Quick Summary

Kefir can cause temporary digestive issues like gas, bloating, and cramping as your gut adjusts to new probiotics. Certain individuals, including those with compromised immune systems or milk allergies, should exercise caution. Adverse reactions can be minimized by starting with a small amount.

Key Points

Initial Digestive Discomfort: New kefir drinkers may experience temporary gas, bloating, and cramping as the gut microbiome adjusts to the high probiotic load.
Start Slowly to Minimize Side Effects: A gradual increase in consumption, starting with just a tablespoon or two, helps the body adapt more comfortably.
Who Should Be Cautious: Individuals with compromised immune systems, milk allergies, or histamine intolerance should consult a doctor before consuming kefir.
Check for Hidden Sugars: Flavored commercial kefirs often contain high levels of added sugar, which is a concern for diabetics and others limiting sugar intake.
Potential Medication Interactions: Kefir can interact with certain medications, including immunosuppressants, antibiotics, and disulfiram.
Non-Dairy Options Are Available: For those with milk protein allergies or lactose sensitivity, water kefir is a dairy-free alternative that still provides probiotic benefits.

Common Side Effects for Beginners

For many newcomers, the journey with kefir starts with a few minor, and often temporary, digestive disturbances. These initial reactions are usually a sign that your gut microbiome is adjusting to the new influx of beneficial bacteria and yeast. This is sometimes referred to as a “healing crisis” or Herxheimer reaction. Your body is simply rebalancing its ecosystem. The most common side effects include:

Bloating and Gas: This is arguably the most frequent complaint when starting kefir. It occurs because the live microbes begin feasting on carbohydrates in your gut, producing gas as a byproduct. This typically subsides as your system gets used to the new population of microbes.
Cramping and Abdominal Discomfort: Mild stomach cramps can accompany the initial gas and bloating. For those with a sensitive digestive system or underlying issues like Irritable Bowel Syndrome (IBS), this can be more noticeable.
Changes in Bowel Movements: Both constipation and diarrhea have been reported by individuals starting kefir. The effect can depend on the specific fermentation process and individual gut health, with some batches having a more laxative effect and others potentially constipating if your system is particularly sensitive.
Nausea: A feeling of nausea can sometimes occur, particularly if too much is consumed too quickly.
Taste Changes: Some may experience a temporary alteration in their sense of taste as their body adjusts to the new probiotic load.

Why Do These Side Effects Happen?

The side effects are not a sign of kefir being 'bad' but rather an indication that the potent probiotics are beginning their work. They are outcompeting less beneficial microbes, which can lead to a temporary die-off effect as the gut environment shifts toward a healthier balance. For the majority, these symptoms pass within a couple of weeks of consistent, moderate consumption.

Who Should Exercise Caution with Kefir?

While largely safe, kefir is not suitable for everyone. Certain individuals should approach its consumption with care and, ideally, under the supervision of a healthcare provider.

Immunocompromised Individuals: People with weakened immune systems due to conditions like HIV/AIDS or undergoing chemotherapy are more susceptible to infections. The live bacteria and yeast in kefir, while normally beneficial, could pose a risk.
Those with Milk Allergies: A true milk allergy is an immune reaction to the proteins in milk, primarily casein. While milk kefir contains less lactose, it still contains milk proteins and should be avoided. Non-dairy alternatives like water kefir or coconut milk kefir are safer options.
Individuals with Histamine Intolerance: As a fermented food, kefir is naturally high in histamines. For those with histamine intolerance, consuming it can trigger symptoms like headaches, skin rashes, and digestive upset.
People with SIBO or Candida Overgrowth: Kefir contains both probiotics and prebiotics. In cases of Small Intestinal Bacterial Overgrowth (SIBO) or Candida overgrowth, introducing a high load of new microbes too quickly can exacerbate gas, bloating, and other digestive issues. A very slow introduction is recommended, or possibly avoiding it entirely during treatment.
Diabetics (especially with flavored varieties): Plain, unsweetened kefir may help regulate blood sugar levels. However, many commercial fruit-flavored kefirs are loaded with added sugar, which can cause unwanted blood sugar spikes. Reading labels carefully is crucial for individuals with diabetes.

Potential Medication Interactions

It is important to discuss kefir consumption with your doctor if you are on certain medications. The live cultures in kefir may affect how some drugs work or are absorbed. Notable interactions include:

Immunosuppressants: Kefir should be avoided by those taking these drugs, as the immune system is already suppressed and live cultures could increase the risk of infection.
Antibiotics: These medications kill bacteria indiscriminately, including the beneficial ones in kefir. It is often recommended to space out the consumption of kefir from the antibiotic dose by a few hours to maximize benefit.
Disulfiram (Antabuse): Kefir contains a trace amount of alcohol due to fermentation. While minimal, those on disulfiram should avoid kefir to prevent unpleasant side effects.

How to Minimize Initial Side Effects

If you are a beginner looking to enjoy the benefits of kefir with minimal discomfort, following these simple guidelines can help your digestive system adjust smoothly:

Start Small: Begin with a very small amount, such as 1–2 tablespoons, and gradually increase your intake over a week or two. This allows your gut time to adapt without being overwhelmed.
Choose Plain: Stick to plain, unsweetened kefir initially. Added sugars can feed less beneficial bacteria and contribute to gas and bloating.
Stay Consistent: Regular, small doses are more effective for establishing a healthy gut flora than sporadic, large servings.
Drink with Food: Taking kefir with a meal can help buffer its effects and reduce the likelihood of digestive upset.
Consider Water Kefir: If you are particularly sensitive to dairy or lactose, water kefir can be a great dairy-free, probiotic alternative.

Water Kefir vs. Milk Kefir: A Side-by-Side Look


Feature	Milk Kefir	Water Kefir
Source	Animal milk (cow, goat, sheep)	Sugar water or fruit juice
Key Side Effect	Dairy-related (mild lactose, protein)	Sugar-related (if sweetened)
Probiotic Diversity	High, including bacteria and yeasts	High, includes bacteria and yeasts
Texture	Creamy and tangy, like drinkable yogurt	Fizzy and light, similar to kombucha
Lactose Content	Very low, but not zero	Non-existent, suitable for milk allergies
Suitable for Vegans	No, unless made with non-dairy milk	Yes

Conclusion: Safe Enjoyment of Kefir

For the vast majority of healthy adults, drinking kefir is safe and can be a valuable addition to a balanced diet. The common side effects experienced by beginners, such as bloating and gas, are typically temporary as the gut microbiome adjusts to the probiotic-rich beverage. However, it is crucial to recognize that certain groups, including those with compromised immune systems or diagnosed allergies, should exercise caution and consult a healthcare professional. By starting with small doses and listening to your body, you can safely introduce kefir and enjoy its many potential health benefits.

For more in-depth information on probiotics and digestive health, resources like WebMD provide authoritative guidance.

Frequently Asked Questions

Yes, bloating is a common and normal side effect when you first start drinking kefir. Your gut flora is adjusting to the new probiotics, and the gas produced by fermentation can cause temporary discomfort that typically resolves with continued use.

Many people with lactose intolerance can tolerate milk kefir because the fermentation process significantly reduces its lactose content. However, those with severe intolerance may still have issues and should consider a non-dairy alternative like water kefir.

Individuals with severely compromised immune systems (e.g., HIV/AIDS, post-chemotherapy), true milk protein allergies, or a history of histamine intolerance should avoid kefir unless advised by a doctor.

Yes, kefir can interact with certain medications. It should not be taken with immunosuppressants or disulfiram, and consumption should be spaced out from antibiotics to maximize probiotic effectiveness.

Yes, for those who experience dairy-related side effects, water kefir is a suitable alternative. It is dairy-free and can provide similar probiotic benefits, though it's important to check the sugar content of flavored varieties.

To reduce side effects, start with a small amount (1–2 tablespoons) and increase slowly. Choose plain, unsweetened kefir and consider drinking it with a meal. For those with sensitive guts, a very gradual introduction is key.

The Herxheimer reaction, or 'healing crisis,' is a temporary reaction to the detoxification process that occurs as the new, good bacteria in kefir kill off bad bacteria in the gut. Symptoms can include flu-like feelings, headaches, and general malaise, but they typically pass within a couple of weeks.