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Alcohol Intolerance: Signs, Causes & How to Test

Last Updated: March 3, 2024

Editorial Policy | Research Policy

Many people enjoy using alcohol in social gatherings or to relax. For some people, however, drinking unexpectedly causes discomfort and adverse reactions, making them wonder about the effect alcohol is having on them. 

Alcohol intolerance is a condition that is often misunderstood yet significantly impacts the lives of those affected by it. Understanding the signs, causes, and testing methods for alcohol intolerance is the first step toward addressing and managing this condition effectively.

What Is Alcohol Intolerance?

Alcohol intolerance is a condition where someone reacts negatively to alcohol and is caused by the way their body metabolizes (or breaks down) alcohol. Unlike the expected effects of alcohol that most people experience, those with alcohol intolerance may face immediate and uncomfortable symptoms even after consuming small amounts. 

This condition is primarily due to the body’s inability to metabolize or break down alcohol properly. Under normal conditions, alcohol is broken down into a chemical called acetaldehyde, which is then broken down further into acetate, which can be easily eliminated. In someone with alcohol intolerance, the enzyme that breaks down acetaldehyde doesn’t work correctly, leading to a buildup of acetaldehyde. This toxic by-product of alcohol metabolism quickly triggers a range of symptoms that can be both unpleasant and potentially harmful.

Alcohol intolerance is distinctly different from having a lower tolerance for alcohol’s intoxicating effects, although the two are often confused. Individuals with alcohol intolerance are genetically predisposed to have inadequate amounts of the enzyme needed to metabolize alcohol efficiently. As a result, even a minimal intake of alcohol can lead to noticeable and often severe reactions, distinguishing this condition from the typical experience of over-intoxication.

Alcohol Allergy vs. Intolerance

It is important to distinguish between alcohol allergy and alcohol intolerance, as the two terms are often mistakenly used interchangeably. Alcohol allergy is an immune system response to certain ingredients in alcoholic beverages, not to the alcohol itself. This leads to an allergic reaction. 

In contrast, alcohol intolerance is a metabolic issue related to the breakdown of alcohol in the body. While symptoms may sometimes overlap, alcohol allergies can provoke a more severe reaction, potentially life-threatening, such as anaphylaxis. On the other hand, alcohol intolerance symptoms, although uncomfortable, are generally less severe and more manageable.

Causes of Alcohol Intolerance

The primary cause of alcohol intolerance is a genetic mutation that affects the production of enzymes responsible for alcohol metabolism, mainly aldehyde dehydrogenase (ALDH2). This enzyme plays a crucial role in breaking down acetaldehyde. A deficiency or inactivity of ALDH2 leads to the accumulation of acetaldehyde, triggering various intolerance symptoms. Other factors, such as certain medications or health conditions, can also interfere with the normal function of ALDH2, causing intolerance symptoms or mimicking intolerance reactions.

How Does Sudden Onset Alcohol Intolerance Occur?

Sudden onset alcohol intolerance can be perplexing and concerning when it develops. Genetic alcohol intolerance will be present during your entire life, so if it suddenly starts, it is typically due to another reason. The most common cause is starting a new medication that inhibits the enzymes needed to metabolize alcohol, leading to new intolerance symptoms. Metronidazole (Flagyl) and disulfiram (Antabuse) are the most common medications that cause this.

There are other potential causes, such as the onset of certain health conditions, especially some types of cancers, that can significantly impact the body’s ability to process alcohol. These conditions can reduce enzyme efficiency or cause changes in the body’s reaction to toxins, leading to a sudden intolerance to alcohol where none was evident before. While alcohol intolerance from health conditions is very rare, it is crucial to consider these factors and consult your doctor if you notice a sudden change in how your body reacts to alcohol.

Symptoms of Alcohol Intolerance

Recognizing the symptoms of alcohol intolerance is essential for understanding and managing this condition. Symptoms can vary in severity and may include:

  • Flushing or redness of the face and neck
  • Increased heart rate or heart palpitations
  • Nasal congestion or a runny nose
  • Nausea or vomiting
  • Headache
  • Low blood pressure
  • Diarrhea
  • Worsening of pre-existing asthma or allergic reactions

Of these symptoms, facial flushing is the most common and will almost always be present. With alcohol intolerance, these symptoms will begin almost immediately after exposure to alcohol. While drinking alcohol is the most common trigger, other actions, like using cough syrup containing alcohol or alcohol-based hand sanitizer, may also trigger these symptoms.

Alcohol Intolerance Testing

If you suspect you might have alcohol intolerance, you will need a doctor to obtain a diagnosis. There are several testing methods your doctor will use to help confirm the diagnosis. Skin tests can determine if you have an allergy to specific components found in alcoholic beverages and are used to rule out the possibility of an alcohol allergy. Once alcohol allergy has been ruled out, the diagnosis for alcohol intolerance is typically based on your reported symptoms and a detailed medical history. 

Genetic testing may also be an option, providing a more definitive answer. This test can identify variations in the ALDH2 gene, confirming whether the intolerance is due to genetic factors. While these tests can be insightful, they must be conducted under a doctor’s orders, ensuring that the results are interpreted correctly and that any underlying health concerns are addressed.

Can Alcohol Intolerance Be Treated?

Currently, there is no cure for alcohol intolerance, but understanding and managing the condition can significantly reduce its impact. If alcohol intolerance is caused by something else, such as the use of a medication, then addressing the underlying cause may eliminate alcohol intolerance. 

For those with genetically-caused alcohol intolerance, the most straightforward approach is to avoid alcohol altogether, preventing the onset of symptoms. Because acetaldehyde is toxic and carcinogenic (causing cancer), avoiding alcohol altogether is the only option that medical professionals will recommend.

Those who still want to drink should moderate intake and choose alcoholic beverages with lower congener content (substances produced during fermentation) can help minimize reactions. In some cases, antihistamines or other medications may help alleviate certain symptoms like flushing or nasal congestion. However, these should be used cautiously and under a physician’s guidance, as they do not address the root cause of alcohol intolerance and may have side effects. 

Ultimately, if you suspect you have alcohol intolerance, consulting with healthcare professionals is the best course of action. They can provide personalized advice, support, and treatment options, helping you effectively navigate the challenges of this condition.


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