Mixing energy drinks with alcohol could be a risky combination, leading to a greater risk of accidents and injuries, research from Canada suggests.
The caffeine contained in energy drinks can make people feel wide awake and encourage them to drink more than normal.
Medics say this could also cause problems sleeping and a raised heart rate, although more research is needed.
Charity Drinkaware does not recommend mixing alcohol and energy drinks.
Mixing spirits and liqueurs with energy drinks, such as Red Bull and Monster, has become increasingly popular - in pubs and clubs, and at home.
But recent research suggests that drinking alcohol mixed with high-caffeine energy drinks could be more risky than drinking alcohol on its own, or with a more traditional mixer.
This is because it can make people "wide awake drunk" - a result of the stimulating effects of caffeine and the brain-slowing effects of alcohol.
What are the risks?
In a review of 13 studies published between 1981 and 2016, researchers at the University of Victoria, Canada, found a link in 10 studies between intake of alcohol mixed with energy drinks and an increased risk of falls, fight and accidents.
But they said they were unable to pin down the size of the injury risk because of the varied nature of the studies and the difficulty of comparing results.
When it comes to the question of whether mixing alcohol and energy drinks is harmful to health, larger studies are still needed to work this out.
At present, the Food Standards Agency and the Committee of Toxicity says the evidence is not clear.
What is in energy drinks?
Energy drinks contain high levels of caffeine, usually about 80mg in a 250ml can - equivalent to a mug of instant coffee.
In comparison, a 330ml can of classic Coca-Cola contains 32mg and a can of Diet Coke 42mg.
Energy drinks also contain lots of sugar as well as other ingredients, such as glucuronolactone and taurine, and sometimes vitamins and minerals or herbal substances.
Some smaller "energy shot" products can contain as much as 160mg of caffeine in a 60ml bottle.
How much caffeine is too much?
High levels of caffeine can lead to anxiety, panic attacks and increased blood pressure.
Pregnant and breast-feeding women are advised not to have more than 200mg of caffeine over the course of a day.
There is more information on NHS choices.
European advice says that most other adults are safe to drink up to 400mg a day.
Children should have caffeine in moderation - a daily intake of less than 3mg of caffeine per kilogram of body weight in children and adolescents is safe, the European Food Safety Authority says.
Under current UK rules, drinks that contain more than 150mg per litre of caffeine (apart from teas and coffees) must carry a warning saying: "High caffeine content. Not recommended for children or pregnant or breast-feeding women".
But there are currently no legal restrictions on the amount of caffeine that may be present in a food or drink product in the UK.
What are the recommended limits on alcohol?
Men and women should not drink more than 14 units of alcohol a week.
That's equivalent to six pints of average strength beer or seven glasses of wine.
The advice, from the Department of Health, also says that it's best not to save up units and drink them all in one go and to make sure you have alcohol-free days every week.
What's the advice on mixing both?
Audra Roemer, study author and doctoral student in clinical psychology at the University of Victoria, says: "Usually when you're drinking alcohol, you eventually get tired and you go home.
"Energy drinks mask that, so people may underestimate how intoxicated they are, end up staying out later, consume more alcohol, and engage in risky behaviour and more hazardous drinking practices."
The charity Drinkaware said anything that encouraged people to drink more alcohol was "a very risky thing to do, and a worrying trend".
But Gavin Partington, director general at the British Soft Drinks Association, said there was no indication that energy drinks had any specific effect related to alcohol consumption.
"The European Food Safety Authority has concluded that it is unlikely that caffeine interacts adversely with energy drinks or with alcohol," he said.
"However, anybody drinking alcohol should do so in moderation, whether or not it's mixed with an energy drink."
Any top tips?
If you're going to mix alcohol and energy drinks, then try to reduce any risks by:
- keeping a close eye on how much you and your friends are drinking
- eating food such as pasta or potatoes before a night out
- tracking the caffeine and sugar content of energy drinks
- avoiding drinking them before going to bed