Alcohol intolerance is when someone’s body cannot process alcohol normally. This results in the buildup of a chemical called acetaldehyde, which causes uncomfortable symptoms that are typically considered worse than any pleasure alcohol brings. 

Alcohol intolerance is relatively uncommon, and many people who have problems drinking alcohol actually have an alcohol allergy — not alcohol intolerance. With an alcohol allergy, your body’s immune system attacks a component of the alcohol, while with alcohol intolerance, your body fails to process alcohol correctly.

What Is Alcohol Intolerance?

Alcohol intolerance occurs when there is a disruption in how someone’s body breaks down alcohol. Usually, alcohol is broken down into a chemical called acetaldehyde. This chemical is almost immediately converted into other chemicals by an enzyme called aldehyde dehydrogenase. A deficit or inhibition of this enzyme leads to alcohol intolerance and causes acetaldehyde to build up.

Prolonged acetaldehyde exposure can be harmful. However, the acetaldehyde buildup caused by alcohol intolerance does not last long enough to cause truly dangerous effects unless you drink frequently. Its temporary effects are still uncomfortable and can cause headache, nausea, stuffiness and other unpleasant symptoms.

Alcohol Allergy vs. Intolerance

Alcohol intolerance is quite uncommon, and many people who think they may have an alcohol intolerance actually have an alcohol allergy. An alcohol allergy is very different from alcohol intolerance and occurs when the body’s immune system attacks something found in alcohol.

The alcohol itself almost never causes alcohol allergies. More commonly, they are related to a component of alcohol, such as grapes, hops or barley. Someone with an alcohol allergy may not be allergic to all forms of alcohol equally.

What Causes Alcohol Intolerance?

Several things can cause alcohol intolerance, with your genetics being the most likely culprit. DNA changes affecting the enzyme aldehyde dehydrogenase will cause alcohol intolerance that will last throughout the lives of those with it. People of Asian heritage most commonly have genetic-based alcohol intolerance; however, it can affect anyone.

Medications can also cause alcohol intolerance. Certain antibiotics can inhibit aldehyde dehydrogenase, leading to alcohol intolerance. In this situation, alcohol intolerance may be called a disulfiram reaction. The medication disulfiram (Antabuse) is sometimes used to deliberately cause this reaction, as it can help discourage people from drinking alcohol when trying to quit.

In addition, alcohol intolerance can be caused by certain diseases. While this most commonly occurs with Hodgkin’s lymphoma, a type of cancer, many diseases can cause alcohol intolerance. However, only a small percentage of people with these diseases develop alcohol intolerance.

What Causes a Sudden Alcohol Intolerance?

Sometimes, people who have previously been able to use alcohol may suddenly develop alcohol intolerance. This is usually caused by one of two things:  

1. A medication that causes alcohol intolerance has been started. This is often related to an antibiotic called metronidazole (Flagyl), but other medicines may also cause this.
2. It is not actually alcohol intolerance; rather, it is an alcohol allergy that has suddenly started. Allergies can develop suddenly and unpredictably.

Alcohol Intolerance Symptoms

Alcohol intolerance symptoms are caused by the buildup of acetaldehyde in the bloodstream. These symptoms include:

• Flushing in the face
• Stuffy nose
• Headache
• Abdominal pain
• Nausea or vomiting
• Diarrhea
• Hives
• Low blood pressure
• Worsening asthma
• Migraines
• Severe allergic reaction

These symptoms occur almost immediately after using alcohol. They may even be caused by exposure to alcohol from sources other than alcoholic beverages. For example, using cough syrup with alcohol or an alcohol-based hand sanitizer can lead to alcohol intolerance symptoms.

Testing for Alcohol Intolerance

If you suspect you have alcohol intolerance and are planning to drink again, you should see a doctor. A physician can determine if you have alcohol intolerance, help you understand what you can do about it and explain any potential implication the condition has on your health. 

There is no specific test used to evaluate alcohol intolerance. However, genetic testing can determine whether you have the genes associated with lifelong, inherited alcohol intolerance. Testing for alcohol allergies can also help rule out alcohol intolerance as a possibility. If you have an alcohol allergy, testing can also help figure out what components of alcohol you are allergic to.

The diagnosis of alcohol intolerance is usually made by ruling out alcohol allergy as a cause of these symptoms. It also involves evaluating the symptoms that occur and how connected they are to alcohol use.

Can Alcohol Intolerance Be Treated?

Alcohol intolerance does not go away if it is caused by genetics. While some medicines can reduce some of the symptoms of alcohol intolerance, they will still be present. Drinking alcohol when you have alcohol intolerance can lead to chronic acetaldehyde exposure, which is associated with health concerns such as an increased risk of cancer and other problems. Someone with genetic alcohol intolerance will typically be discouraged from ever using alcohol.

If alcohol intolerance is due to medication use, it is much easier to treat. In these cases, alcohol should be avoided while taking the medicine, or the medicine should be changed. This should quickly resolve any problems caused by the medicine.