The just-published survey of thousands of New Zealanders has found a heightened risk of caffeine use disorder (CUD) among people who consume even a moderate amount of it.
"This means having two to three cups of coffee or a can of energy drink every day can make the person more likely to experience problems," said Dr Simone Rodda, of the University of Auckland's School of Population Health.
After surveying around 2400 New Zealanders, Rodda and her team found about three quarters consumed caffeine at least every day – and one in five met the proposed criteria for CUD.
The research - which quizzed participants on how often they consumed a wide range of different caffeinated products, also delved into trends around harm, age and gender - also indicated that women and smokers are at greater danger of addiction.
While caffeine has long been known to have an effect on people – research on it dates back to the beginning of the 19th century, while the term "caffeinism" began popping up amid studies around the 1960s and '70s – scientists are still working to understand its addictive properties.
But Rodda said the current body of evidence was now clear: physiologically, caffeine was an addictive substance, so going cold turkey could bring on withdrawal problems.
Caffeine use withdrawal now happened to be included in the latest edition of psychiatry bible, the Diagnostic and Statistical Manual of Mental Disorders (DSM).
The study found many New Zealanders experienced symptoms of caffeine withdrawal. Nearly half reported fatigue and drowsiness and about a third suffered headaches or had difficulty concentrating.
Yet there wasn't enough evidence to include CUD itself in the DSM, partly because of a lack of severe negative consequences.
"Our study found, however, that 85 per cent of participants reported some harms from the caffeine use," Rodda said.
"These included psychological harms like feeling dependent as well as physical like insomnia, dehydration, irritability or a desire for sugar, when caffeine in the body reduces."
Another alarming insight from the survey was that the risk of CUD and harm among people who consumed between 200mg and 400mg of caffeine a day - equivalent to two to three cups of coffee - was almost the same as for people who consumed more than 400mg.
"Why was it alarming? Because current international recommendations are that consuming under 400mg of caffeine a day is not harmful," Rodda said.
"Our findings pointed out that current recommended safe limit might not be that safe."
Whether a person could develop CUD very much depended on their factors like habit, or close access to caffeine.
"We have become a café culture whereby we meet for coffee, go out for coffee and have fancy machines in our home," she said.
"It is literally the most accessible and prolific mind-altering substance that is consumed every day by most people. When problems develop, it is usually because something has changed in the person's environment."
Students, for example, were often prone to caffeine problems because of periods of high stress like exams, so gradually used more and more to get the same effects.
Soon enough, they found they had to keep their consumption going to avoid withdrawal symptoms, locking themselves into a vicious cycle.
Rodda's research programme at the university explores strategies used by people to limit such unwanted behaviours, ranging from gambling and gaming, to sugar and pornography.
"Recently, we looked at caffeine as well and found that actually quite a lot of people try different methods to cut back or limit their use," she said.
"As part of this study we discovered that there was very limited information on consumption in New Zealand and we really struggled to understand whether it was even a problem.
"There has been research on energy drinks – but we noticed almost nothing on coffee."
Rodda herself was more than aware of the dangers of drinking too much coffee - something she realised she was doing a few years ago.
"I knew this because I started to feel generally a bit anxious and would get very moody if I didn't have the morning cup. I also found out that sugar has a half life of six hours - meaning if you have a latte at 9am by 3pm you need more.
"I was like a lot of people – not wanting coffee at 3pm because it might keep me awake later but also wanting a pick-me-up. I noticed I was turning more and more to sugar as that quick fix."
Eventually, she quit coffee for two years, and found the change tough.
"I had to stay in bed for a whole weekend to get through the first days of withdrawal. I used a bunch of strategies including decaf and soda water as well as meeting people for a walk instead of coffee."
Her team has now made good progress toward creating an effective intervention for caffeine reduction, which has been based on real-life experiences like her own.
The most common techniques were substance substitution - swapping caffeine for decaf or tea - finding out if the amount they were consuming really was addictive or fell within safe limits, or just avoiding it altogether, along with cafes.
For those moderate coffee drinkers among us, what was the big take-away?
"People can and should enjoy a cup of coffee or a glass of soda. The key is to listen to your body," she said.
"Some people find that one cup a day is all they can tolerate but for, others two or three is fine.
"If they notice any harm, like increased anxiety, irritability or headaches then perhaps look at cutting back.
"People in professions that are stressful should also keep an eye on their consumption. My advice is to use it – don't abuse it."
The new research has been published in the journal Addictive Behaviours.
