An estimated 75% of Australians drink at least one cup of coffee per day. Coffee drinkers report loving the taste and the way a warm cup of coffee makes them feel. From the increased focus to the mood boost, coffee’s simply the best.

But like all good things, there’s a flipside: Too much caffeine can make you feel incredibly anxious and stressed.

Caffeine (the world’s most widely-used psychoactive drug) is a stimulant found in coffee, tea, soda, and chocolate. It can also be hiding in some medications and supplements, particularly weight control products. And, of course, in energy drinks, which can contain excessive amounts of caffeine.

According to HealthDirect, caffeine is generally safe in moderate amounts (under 400 milligrams daily) for healthy adults. Coffee, which is how the majority of us get our daily dose, typically contains 80 to 100 milligrams of caffeine per cup. A stronger brew will naturally contain more. Meanwhile, there’s anywhere from 40 to 250 milligrams of caffeine per cup in energy drinks.

Energy drinks also contain plant-based chemicals that have a stimulatory effect or build upon the available caffeine in the beverage, says neuroscientist, Dr James Giordano, who warns against mixing coffee with other stimulants.

How does too much caffeine increase stress?

Once caffeine is absorbed in the bloodstream, it passes up to the brain where it blocks chemicals known as adenosines, which cause drowsiness. This increases activity in the brain that stimulates your central nervous system, activating your body’s stress response.

The result is a cascade of chemical reactions, including the release of adrenaline and cortisol (the stress hormone), that prepare your body for “fight or flight.” Not only do you feel more alert, your heart also beats faster, blood flow increases, and muscles tense—all of which can be helpful in small doses.

However, there’s a point at which caffeine can be overstimulating and lead to adverse effects, like the jitters, says neuropsychologist, Dr Jen Wolkin.

“Imagine muscles that are being prepped for sudden exertion but there’s nowhere to go. This translates into what we know as the jitters,” she explains. The increased blood flow and heart contractions can even lead to palpitations, which can feel like a panic attack.

It’s like adding fuel to the fire, according to Dr Lina Begdache, a nutrition scientist. “In small amounts caffeine can actually boost your mood,” she says. But if you exceed certain levels, it will increase (and prolong) the stress response past the point of being helpful.

Can caffeine make anxiety worse?

According to Wolkin, research indicates that caffeine can aggravate and maintain an anxiety disorder. The impact of coffee can be so pervasive and play such a clear role in exacerbating someone’s anxiety that she asks all new patients about their caffeine consumption.

If she later notices that coffee is intensifying, or helping to maintain, some of the anxiety a person is experiencing, she recommends weaning off slowly in conjunction with their therapeutic work.

Caffeine use can also become a vicious cycle for those with underlying anxiety, according to psychologist Jenicka Engler, PhD. For example, someone with anxiety may be dealing with fatigue due to trouble sleeping, so they’ll turn to coffee to perk up throughout the day. But, in turn, glugging down too much caffeine makes them feel even more anxious and prevents them from falling (and staying) asleep at night. And then the cycle repeats.

How many cups of coffee are too many?

It depends. Caffeine affects all of us differently for various reasons, including bodyweight, gender, tolerance, and so on. But in general, around two cups of coffee (200 milligrams of caffeine) won’t cause a great deal of symptoms for the average person, according to Dr Rashmi Goyal, an internal medicine specialist.

“Over 400 milligrams of caffeine (about 4 cups of coffee) may bring out symptoms of anxiety,” Dr. Goyal says. Drinking more than 1,200 milligrams can even cause seizures in some individuals.

“Imagine muscles that are being prepped for sudden exertion but there’s nowhere to go.”

However, that all depends on personal sensitivities and rates of metabolism. People who metabolise caffeine at slower rates end up compiling more caffeine in their system, and are thus impacted by fewer cups of coffee. Rapid metabolisers absorb, break down, and eliminate caffeine more quickly, so they can generally drink more cups before feeling anxious.

There are certain people who have a genetic defect in the liver enzyme that metabolises caffeine, explains Begdache, which makes them slow metabolisers. Caffeine also affects young people, who have more sex hormones competing with caffeine for metabolism, and women in general, who have higher levels of oestrogen and are more susceptible to mood disorders.

Some people may also be more sensitive to caffeine, says Dr. Giordano, perhaps due to certain medications or an underlying condition that makes them more predisposed to caffeine’s stimulating effects.

How to find your caffeine threshold

Since there’s not a one-size-fits-all dose of caffeine for everyone, it’s important to determine your own threshold. The main way to do that is to pay attention to how you feel as you drink coffee or other caffeinated drinks throughout the day.

For me personally, I become anxious and a little weepy in the early afternoon when I’ve overdone it. You may become restless or easily agitated. Someone else may notice that they start tossing and turning throughout the night after that late afternoon Starbucks run.

“It definitely takes some level of interoceptive awareness, which is awareness of our own inner body sensations,” explains Wolkin. When you start to feel tense, jittery, and like everything’s sped up—that’s a clue you’ve reached your limit. Take note of how much caffeine you’ve had once those feelings surface and aim to cap your intake before you hit that amount.

But experts warn against quitting cold turkey. The symptoms of caffeine withdrawal are very real and unpleasant, leading to headaches, fatigue, difficulty concentrating, irritability, and even muscle pain.

Giordano recommends gradually tapering off the amount of caffeine you drink in a day, allowing your system to return to normal in a more metered way. If you’re a coffee drinker, the Cleveland Clinic recommends alternating between regular and decaf at first, particularly if the taste of coffee is what you’re really after. (Coffee has a very strong conditioning effect that can act as a placebo due to its smell and taste, says Giordano.)

Try this for at least two to three weeks—gradually bringing down the amount of caffeine you drink in a day—and see what it does for you. This way, you can wean off slowly and return to an amount that feels healthy for you.