Maybe you never feel the effects of caffeinated beverages, or an espresso used to help kick-start your morning, but now it’s doing nothing for your energy levels. Either way, there are many reasons why caffeine may not be working for you.
Below, we dive into the six main reasons why caffeine isn’t affecting you. Plus, we cover ways to get the energy-boosting benefits of caffeine and how you can improve your energy without relying on caffeine at all.
Want to master the art of consuming caffeine? We’ve answered every question you could have about caffeine, sleep, and energy here.
We’ve already covered reasons why caffeine makes you feel tired, but if caffeine is having no effect on you at all, here are the main culprits:
Sleep debt is how much sleep you owe your body over the last 14 nights. It’s measured against your sleep need, the genetically determined amount of sleep you need each night.
If you’ve got a lot of sleep debt, no amount of caffeine is going to make you feel more awake. In fact, one study found after three nights of five hours of sleep a night, caffeine no longer boosted alertness or performance.
Everything from your focus to your mental health to your physical performance will take a hit when you’re suffering from sleep deprivation. Plus, it’s a vicious cycle. If you’ve been finding caffeine hasn’t been working for you, you may have been reaching for more of it each day, which has been keeping you up later, building up your sleep debt, and making you feel even more tired.
That sleepiness you feel is all down to adenosine, a chemical that naturally builds up in your body all the time you’re awake. It acts as a neurotransmitter, telling the brain when to rest, and depressing the central nervous system. When it reaches a certain level, you’ll feel drowsy and get the urge to sleep. And when you do sleep, adenosine is purged from your system, so you wake up feeling less sleepy, and the cycle starts again.
Caffeine works by temporarily blocking the adenosine receptors in your brain. But if you haven’t been meeting your sleep need, you’ll have a lot of adenosine in your system, meaning you’ll feel the sleepiness effect of the chemical, even with caffeine in your system.
Working out how much sleep debt you have doesn’t have to be difficult. The RISE app uses your phone use behavior to calculate your sleep need, giving you a number to aim for each night. The app then works out if you’re carrying any sleep debt and, if so, how much exactly.
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You know that afternoon slump when you suddenly feel sluggish? That’s your circadian rhythm at play. This is the internal body clock that runs on a roughly 24-hour cycle, dictating when you feel awake and when you feel sleepy. We all experience natural peaks and dips in our energy levels throughout the day, with one of those dips being in the afternoon.
You’ll feel this dip in energy more strongly if you’re carrying a lot of sleep debt. But even if you’re not sleep deprived, you’ll still feel it — it’s a natural part of your biology. So, if you’re sipping a coffee and feel like it’s doing nothing for you, it may just be because you’re in a natural dip in energy.
While you can’t stop this from happening, you can make it feel better by keeping sleep debt low, and you can plan for it. RISE can predict your circadian rhythm each day, showing you the timings of your energy peaks and dips. You can then schedule less-demanding tasks for this afternoon dip in energy.
Be careful not to rely on caffeine to get you through the afternoon slump. Consuming caffeine too close to bedtime will make it harder to fall asleep and meet your sleep need. This means more sleep debt, and more tiredness during the next day’s afternoon energy dip.
If caffeine used to perk you up, but you now can’t feel its stimulating effects, you may be suffering with caffeine tolerance. This is when your body gets used to the amount of caffeine you usually have, and starts needing more of it to give you the same energy boost.
One study looked at participants who either consumed caffeine or a placebo for 18 days, and then exposed them both to caffeine. The results showed those who had been consuming caffeine already didn’t feel the effects of caffeine as much as those who had been taking a placebo.
Other researchers suggest a caffeine tolerance can develop in as little as three to five days, so coffee lovers who can’t get through the day with a cup — or three — will definitely have a tolerance to it of some kind.
While having too much caffeine certainly comes with its downsides — think sleep loss and caffeine tolerance — having too little can mean it simply won’t work on you. The amount of caffeine we need to feel its effects is different for all of us — it all depends on things like our weight, age, and genetics (more on that soon).
A 2019 meta-analysis compared several studies with different caffeine intakes to see whether low doses were as effective as higher doses. While there were many studies showing no difference, there were some that found higher doses had more of an effect.
For example, one study found a dose of about 2 mg of caffeine per pound of bodyweight (342 mg for the average sized woman (171 lbs) and 400 mg for the average sized man (200 lbs)) improved aerobic endurance performance more than a dose of about 1.45 mg per pound did, which in turn improved it more than a dose of about 0.95 mg per pound. Another study found a dose of about 2.3 mg of caffeine per pound of bodyweight enhanced maximum knee flexion, whilst about 1 mg of caffeine per pound didn’t.
The researchers, Craig Pickering and John Kiely, wrote:
“The currently accepted optimal caffeine dose may not be optimal for everyone. Some individuals may benefit from lower doses of caffeine…, whilst others may need higher doses.”
That’s right, it may not be anything you’re doing. Your genetics determine how you respond to caffeine.
You may not have very “sticky” adenosine receptors, meaning caffeine will have a harder time binding to them to do its job blocking the sleepiness effects of adenosine.
Plus, the enzymes in your liver dictate how quickly caffeine can be broken down, and so how long it lingers in your system for and how long it takes for the effects to kick in.
CYP1A2 is the main enzyme responsible for metabolizing caffeine, but there are two variants of it. If you have one variant, you’ll metabolize caffeine much faster than people with the other variant, meaning you’ll feel the effects of caffeine much less.
One meta-analysis looked at several studies on genetics and caffeine and concluded that your genetics dictate:
It also found these responses to caffeine change as you age.
Certain medications interact with caffeine and change the way it affects you.
Some medications can slow down your caffeine metabolism, meaning it lasts longer in your system and it’ll take longer for you to feel the effects. This can also increase the likelihood of unwanted side effects — like jitters and headaches — while reducing the good ones, like getting an immediate boost of energy.
This may be one reason you’re not feeling the effects of caffeine straight away.
Here are the medications which can slow down how fast your body breaks down caffeine:
Beyond medication, alcohol can also slow down your caffeine metabolism, changing how it affects you (nicotine, meanwhile, results in increased caffeine clearance).
If caffeine isn’t giving you the buzz it once did, it can be easy to reach for another cup of coffee. But that comes with side effects, including the risk of keeping you up at night and building up sleep debt — not to mention building up your tolerance even further.
Here’s what to do instead if you find caffeine isn’t working for you anymore.
As we explained above, the higher your sleep debt the worse you’ll feel and perform each day. But, luckily, you can actually catch up on sleep and pay down some of this debt.
We recommend keeping your sleep debt below five hours to optimize your energy levels. Carrying more than that? Here’s how to pay it back:
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If you’re finding it takes more and more caffeine to feel the same effects, you can actually reset your tolerance. Try slowly cutting down on the amount of caffeine you consume, allowing your body to get used to the lower amounts. For example, coffee drinkers can replace one cup a day with decaf.
Resist the urge to go cold turkey, as this can make withdrawal symptoms even worse.
Caffeine withdrawal symptoms include:
We’ve covered how long caffeine withdrawal symptoms last here.
If you consume a little caffeine and find it’s not making a difference, increasing this slightly should mean you get the energy boost you’re looking for.
However, be careful not to let caffeine’s effects disrupt your sleep — it can last in your system much longer than you think. You can make sure this doesn’t happen by finding out your caffeine cutoff time. This is the time of day you should stop drinking coffee to allow your body enough time to metabolize it by bedtime.
Beware of all sources of caffeine after this time — that includes coffee, black tea, green tea, energy drinks, and chocolate. Plus, the caffeine content of decaf coffee is lower, but it’s still there, so you should steer clear of it close to bedtime.
Many people’s cutoff time will be around noon, though night owls might be able to enjoy caffeine until about 2 p.m. The RISE app can tell you your unique caffeine cutoff time each day.
There are reasons caffeine isn’t affecting you that you can’t control — like your genetics or being in a natural energy dip during the day. If you need an energy boost and coffee isn’t cutting it, consider these tips:
We’ve covered more ways to wake yourself up here.
Want to increase your energy levels, but caffeine isn’t doing the trick? It may be your genetics, but it could also be the amount of sleep debt you have, a caffeine tolerance you’ve developed, the amount of caffeine you’re having, or medications.
You can improve your energy without relying on caffeine though. The RISE app helps you do this by working out how much sleep debt you have and keeping track of it as you work to pay it back. Plus, if you do drink coffee, the app can tell you when to stop each day to make sure it doesn’t impact your sleep and energy levels.
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