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Anyone who has drunk alcohol will be familiar with how easily it can lower your social inhibitions and let you do things you wouldn’t normally do.

But you may not be aware that mixing certain medicines with alcohol can increase the effects and put you at risk.

When you mix alcohol with medicines, whether prescription or over-the-counter, the medicines can increase the effects of the alcohol or the alcohol can increase the side-effects of the drug. Sometimes it can also result in all new side-effects.

How alcohol and medicines interact

The chemicals in your brain maintain a delicate balance between excitation and inhibition. Too much excitation can lead to . Too much inhibition and you will experience effects like sedation and depression.

Alcohol works by increasing the amount of inhibition in the brain. You might recognise this as a sense of relaxation and a lowering of social inhibitions when you’ve had a couple of alcoholic drinks.

With even more alcohol, you will notice you can’t coordinate your muscles as well, you might slur your speech, become dizzy, forget things that have happened, and even fall asleep.

Medications can interact with alcohol to . Alcohol can interfere with the way a medicine works in the body, or it can interfere with the way a medicine is absorbed from the stomach. If your medicine has similar side-effects as being drunk, those .

Not all the side-effects need to be alcohol-like. Mixing alcohol with the ADHD medicine ritalin, for example, can , increasing your heart rate and the risk of a heart attack.

Combining alcohol with ibuprofen can lead to a higher risk of stomach upsets and stomach bleeds.

Alcohol can increase the break-down of certain medicines, such as . This can make the medicine less effective. Alcohol can also alter the pathway of how a medicine is broken down, potentially creating toxic chemicals that can cause serious liver complications. This is a particular problem with .

At its worst, the consequences of mixing alcohol and medicines can be fatal. Combining a medicine that acts on the brain with alcohol may make driving a car or operating heavy machinery difficult and lead to a serious accident.

Who is at most risk?

The effects of mixing alcohol and medicine are not the same for everyone. Those most at risk of an interaction are older people, women and people with a smaller body size.

Older people do not break down medicines as quickly as younger people, and are often on .

Older people also are more sensitive to the effects of medications acting on the brain and will experience more side-effects, such as dizziness and falls.

Women and people with smaller body size tend to have a higher blood alcohol concentration when they consume the same amount of alcohol as someone larger. This is because there is less water in their bodies that can mix with the alcohol.

What drugs can’t you mix with alcohol?

You’ll know if you can’t take alcohol because there will be a prominent warning on the box. Your pharmacist should also counsel you on your medicine when you pick up your script.

The most common are benzodiazepines (for anxiety, insomnia, or seizures), opioids for pain, antidepressants, antipsychotics, and some antibiotics, like metronidazole and tinidazole.

It’s not just prescription medicines that shouldn’t be mixed with alcohol. Some over-the-counter medicines that you shouldn’t combine with alcohol include medicines for sleeping, travel sickness, cold and flu, allergy, and pain.

Next time you pick up a medicine from your pharmacist or buy one from the local supermarket, check the packaging and ask for advice about whether you can consume alcohol while taking it.

If you do want to drink alcohol while being on medication, discuss it with your doctor or pharmacist first.

Nial Wheate in the past has received funding from the ACT Cancer Council, Tenovus Scotland, Medical Research Scotland, Scottish Crucible, and the Scottish Universities Life Sciences Alliance. He is a Fellow of the Royal Australian Chemical Institute, a member of the Australasian Pharmaceutical Science Association, and a member of the Australian Institute of Company Directors. Nial is the chief scientific officer of Vaihea Skincare LLC, a director of SetDose Pty Ltd a medical device company, and a Standards Australia panel member for sunscreen agents. Nial regularly consults to industry on issues to do with medicine risk assessments, manufacturing, design, and testing.

Kellie Charles was a previous Board Member of the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists.

Associate Professor Tina Hinton has previously received funding from the Schizophrenia Research Institute (formerly Neuroscience Institute of Schizophrenia and Allied Disorders). She is currently a Board member of the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists.

Jasmine Lee does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.