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When it comes to drugs, alcohol and weed are among the most commonly used substances. But what really happens when they team up?

Occasionally mixing alcohol and weed — also known as crossfading — likely won’t lead to major health problems. But there are a lot of variables to consider, including which one you use first and how you consume them.

If you aren’t careful, the duo can lead to a case of the spins or a green out, two reactions that can turn a fun night out into a nauseated night in.

It’s also important to remember that people can have very different reactions to the same mix of alcohol and weed. If you’re out in a group, one person’s reaction might be very different than yours.

Read on to learn more about the potential reactions and what to do if you have a bad one.

Drinking before using weed can intensify weed’s effects. This is because alcohol increases the absorption of weed’s main psychoactive ingredient, delta-9-tetrahydrocannabinol (THC).

This generally results in a stronger high. While this might be nice for some folks, it can cause others to green out. This refers to a range of unpleasant physical symptoms that can result from a strong high.

Symptoms of a green out include:

  • sweating
  • dizziness
  • nausea
  • vomiting

Alcohol before weed: Proceed with caution

Drinking alcohol before using weed can ramp up the effects of THC. If you’re a seasoned pro, this might not be a huge deal. But if you’re sensitive to weed or don’t have much experience using it, it’s best to avoid mixing the two. If you do, move slowly and be sure to listen to your body.

Breaking down the research

Turns out, you might not need much alcohol to change the way your body absorbs THC.

In a 2015 study, 19 participants drank either a placebo or small amount of alcohol. Ten minutes later, they used a vaporizer to inhale either a low or a high dose of THC.

The researchers found significantly higher peak THC levels among participants who had alcohol versus those who had a placebo. This was true for both low and high doses of THC.

However, this study was pretty small, making it hard to draw any firm conclusions. Plus, a similar (but equally small) 2010 study found that alcohol consumption didn’t have much of an effect on THC concentrations.

While there’s some research around the effects of drinking alcohol before using weed, there isn’t much about the opposite approach. The studies that do exist are old and mostly inconclusive.

For example, a 1992 study had 15 participants smoke a placebo, a high dose of THC, or a low dose of THC on three occasions. On each occasion, they’d rank a different dose of alcohol, including a placebo, as a low dose or a high dose.

Weed appeared to slow down the rise of blood alcohol levels after consuming a high dose of alcohol. But a 1993 letter to the editor questioned this result.

If using weed does indeed slow the absorption of alcohol, it might also delay feelings of drunkenness. This might seem like a good thing, but it makes it harder to know how impaired you really are.

For example, you might feel like you’re good to drive, but your blood alcohol level may be well over the legal limit.

Weed before alcohol: Assume you’ve had an extra drink or two

Using weed before drinking alcohol may minimize the effects of alcohol. This means you might be tipsier than you feel, increasing your risk for becoming overly intoxicated.

If you use weed before drinking, pay extra attention to how much you’ve had to drink. To err on the side of caution, assume you’ve had a bit more to drink than you actually have, or aim to drink less than you usually would without using weed.

It’s hard to say. There’s isn’t a ton of high-quality research on the topic. Still, there’s some evidence to suggest that regularly combining alcohol and weed may have some concerning effects over time.

Higher risk of dependence

A 2017 review of existing studies notes that people who use alcohol and weed together tend to consume more of both. This can increase your risk for developing a dependence on alcohol, weed, or both.

Decreased cognitive function

A study from 2011 evaluated performance on cognitive tasks among 21 heavy weed users who had consumed alcohol.

Those who consumed just alcohol had worse cognitive functioning than those who only consumed THC. Those who combined the two had reduced cognitive performance than those who only consumed alcohol.

Over the long term, combining alcohol and weed may be associated with decreased cognitive function and changes in brain structures, such as the hippocampus.

Impaired driving

A number of recent studies also focus on how combining weed and alcohol affects your driving.

In a 2013 study, 80 people participated in six testing sessions. In each session, participants consumed a different combination of placebo, low, and moderate doses of THC and alcohol. Then they completed a driving simulation.

The researchers reported that combining THC and alcohol consistently impaired driving performance, with worse performance during nighttime simulations.

Adding alcohol to a low dose of THC impaired driving simulator scores by 21 percent. Adding alcohol to a high dose of THC impaired driving simulator scores by 17 percent.

The big takeaway? Don’t drive after using marijuana or drinking alcohol. Period.

When mixing weed and alcohol, there are a lot of other variables to consider in addition to which one you use first.

These include:

  • your tolerance to either substance
  • the type and strength of the alcohol
  • whether you smoke, vape, or take edibles
  • the time interval between taking each substance
  • whether you also use other substances, including tobacco or caffeine
  • whether you take medication

The safest bet is to avoid using weed and alcohol together. But if you do decide to mix the two, start slow and keep track of how much you’re consuming of each. Keep a running tab in your phone, if you have to.

Remember, consuming weed and alcohol together can make you feel either more or less intoxicated than you would if you were using just one or the other.

If you take medication, talk to your doctor before using weed, alcohol, or both. They may weaken the effectiveness of your medication or increase your risk for certain side effects.

If you’ve mixed weed and alcohol and are having a bad reaction, it’s probably because alcohol seems to make the high from using weed stronger. The resulting unpleasantness is casually known as a green out. This can happen any time you’ve consumed to much weed — with or without alcohol.

Signs of a green out can include:

  • shivering
  • chills
  • sweating
  • rapid heart rate
  • lightheadedness
  • stomach problems
  • nausea and vomiting
  • paranoia
  • anxiety

How to handle a green out

Whether you’re trying to keep still in a spinning room or breaking out in a clammy sweat, these tips can help you make it through:

  • Stay calm. When it comes to bad reactions, patience is key. Your feelings will go away in time. If possible, find something, such as music, to focus on other than your discomfort.
  • Sit or lie down. If you feel dizzy, find a quiet place to rest until you feel better. If possible, ask a friend to help you get home.
  • Eat or drink to boost your blood sugar. A bit of food or a sugary drink can help relieve dizziness. Try something hearty, like soup broth. If you don’t have any on hand, juice will do.
  • Stay hydrated. Both alcohol and weed can leave you feeling dehydrated. That can lead to dry mouth, headaches, and dizziness. Drink water to put your body back on track.
  • Squeeze a lemon. Lemons contain a chemical compound that may decrease the effects of THC in the brain. Adding lemon juice or zest to some water might help when you’re feeling too high.
  • Smell crushed peppercorns. Similarly, peppercorns contain a compound that some say helps when you’re greening out. To take advantage, crush or grind a handful of peppercorns, then take a long inhale. Just don’t get too close. You don’t want to actually get the pepper in your nose.
  • Talk to someone. If you can, get a trusted friend to keep you company. They can help you stay calm and pass the time.

Usually, a bad reaction to mixing weed and alcohol will pass within a few hours. You may even wake up with some lingering effects the next day.

But if you’ve been drinking a lot, it might be hard to tell the difference between a green out and alcohol poisoning, which can be life-threatening if not treated.

Recognizing alcohol poisoning

Seek emergency medical care if you or someone else is experiencing:

  • vomiting
  • confusion
  • seizures
  • slow or irregular breathing
  • bluish lips or skin
  • low temperature
  • unconsciousness

Remember, consuming weed after drinking alcohol might make you feel less intoxicated, which can lead you to drink more than you usually would.

Both weed and alcohol, together and on their own, are also potentially addictive and can lead to dependence and misuse.

Contact your healthcare provider or call the Substance Abuse and Mental Health Services Administration (SAMHSA) hotline at 800-662-4357 if you find yourself dealing with:

  • cravings
  • lack of control over how much you consume
  • anxiety, restlessness, or negative thoughts when sober
  • irritability and moodiness
  • disinterest in other activities
  • changes in appetite and sleep patterns
  • difficulty fulfilling obligations
  • consuming even when it’s risky
  • trying and failing to quit

It might seem harmless to mix alcohol and weed, but doing so can be a slippery slope toward getting overly intoxicated.

If you want to mix the two, pay careful attention to how much of each you’re consuming, especially if you’ve never mixed them before.

Keep in mind that combining the two may be linked to a decline in cognitive function and an increased risk of dependence.