congeners and hangovers

Evidence based

Congeners and Hangovers – Everything You Need To Know

Afterdrink Author Kathy Caldwell
Kathy Caldwell


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Evidence based

Congeners are produced during the fermentation process of alcohol production. They are biologically active molecules that have been implicated as one of the major causes of your hangover.

The biology of hangovers is a complicated one that involves several different causes including dehydration, toxic build-up of acetaldehyde and poor sleep quality to mention a few.

However, scientists are now focusing more on congeners and how much of an effect they have on hangover symptoms.

But what exactly are congeners and how do they make hangovers worse?

In this article, we’re going to cover everything you need to know about congeners and what you can do to avoid them.

Table of contents

What are congeners?

Congeners are volatile substances produced as natural by-products of the alcohol fermentation process. They are present in much higher quantities in certain types of alcohol which we will cover later.

There are several studies that have shown that drinks containing higher amounts of congeners consistently produce worse hangovers in test subjects.

There are many different compounds that come under the umbrella name of congener. These include:

Methanol is the simplest form of “alcohol” and is produced in small quantities during the fermentation process. When we talk about alcohol we drink, we are usually referring to ethanol.

It looks and smells very similar to alcohol we drink (ethanol). Methanol, however, is far more harmful and damaging to your body.

Methanol is toxic by two mechanisms. Firstly, it has powerful sedating effects on your central nervous system. Secondly, it is metabolized by your liver to produce formaldehyde and formic acid which are highly toxic.

These substances block your cells from using oxygen and induce hypoxia at a cellular level. In simple terms, formaldehyde stops your cells from being able to use oxygen and therefore leads to cellular death.

There have been many cases of methanol poisoning reported in the media from homemade cheap alcohol. Thankfully, however, the amounts of methanol in trusted brands is very small and doesn’t cause harm.

That being said, the small amounts of methanol in your alcohol beverages will still worsen hangover symptoms.

Aldehydes and esters
Aldehydes and esters are highly volatile substances found in small quantities in alcohol you drink. They contribute to the smell and taste of alcoholic drinks.

As very active compounds, they react with other substances in your body including free-radicals. As a result, these volatile reactions are thought to promote inflammation and damage.

You’re probably more familiar with acetone as nail polish remover. It’s another substance produced as a by-product of the fermentation process.

In actual fact, acetone is generally regarded as “safe” and only toxic if consumed in large quantities.

That being said, it’s still regarded as an irritant that could contribute to hangover severity.

Tannins are congeners found in high quantities in red wine. You’ll also find it in tea.

On one hand, tannins are thought to be beneficial to health as they act as antioxidants and protect cells from free radical damage.

On the other hand, tannins are thought to contribute to the classical headache associated with drinking red wine.

The theory is that tannins stimulate the release of histamine and serotonin which causes hangover headache.

It explains why red wine hangover is usually the worst if you’ve ever experienced one.

Which type of alcohol has the most congeners?

So now that we know there are a few different types of congeners we can now move onto which type of alcohol contains most of them.

Generally speaking, darker colored drinks have the highest quantity of congeners whereas vodka and gin have the lowest.

Bourbon is said to have 37 times more congeners than vodka!

Alcohol that has been aged in barrels will have significantly more congeners as they accumulate toxins over the years.

Conversely, vodka is usually filtered several times before the final product is made which clears a lot of the impurities and congeners.

Congeners in alcohol infographic

How do congeners make hangovers worse?

We’ve mentioned four of the main congeners that are found in alcohol earlier in this article. There are a few others also which we didn’t go into such as heavy metals like lead and other organic molecules.

The fact that there are so many different types makes it difficult to carry out research into each individual congener.

To complicate matters, there are great differences in congener amounts between different types of alcoholic beverages. For example, different types of whiskey (bourbon, brandy, Scotch, American, Canadian) have very different amounts of congeners.

The only research so far has shown that drinks with higher congeners always lead to more severe hangovers. For example, a study compared bourbon with vodka and found that overall, those given bourbon had more intense hangovers.

So coming back to the question regarding how congeners make hangovers worse, it seems that there’s an interplay between several different factors. These include toxic effects from congener by-products, the release of inflammatory mediators like histamine, and direct toxic actions of volatile compounds with your cells.

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Can you have an allergy to congeners?

Some of your hangover symptoms can have similarities to an allergic reaction.

For example, developing hives, increased heart rate and your skin turning hot and flushed.

As mentioned before, some congeners are thought to activate the release of histamine which can cause all these symptoms.

Actually being allergic to congeners themselves is unlikely as most are all naturally occurring compounds. By this, we mean that your body produces them naturally as by-products of metabolism in small quantities even without drinking alcohol.

Are congeners bad for you?

In small quantities, the damage caused by congeners is negligible.

High concentrations of methanol is by far the most dangerous of the congeners. Thankfully, however, if you stick to legitimate brands, you’re unlikely to have any problems with this.

Some congeners like tannins even have beneficial effects as it acts as an antioxidant.

Anything else to consider?

When it comes to congeners and hangovers, it all depends on how much you drink.

Hangovers are a sign from your body that you’ve been drinking too much for your liver to handle.

There are a few ways to reduce overall hangover severity by drinking plenty of water throughout your night and eating a meal before consuming alcohol.

But at the end of the day, congeners or not, if you drink enough your hangover will be severe.

Congeners in alcohol: Final words

That brings us to the end of our look into congeners and how they increase the severity of hangovers.

Congeners are natural by-products formed during the production of alcoholic drinks, with darker colored drinks containing a lot more of them.

Anyone who’s ever been unfortunate enough to experience a whiskey or red wine hangover knows that it’s the worst of all. And congers are to blame.

If you’re interested in congeners and alcohol, check out our other aricle on which alcohol gives the least hangover.

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