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Why Doesn’t Caffeine Affect Me? 6 Things To Watch Out For

If caffeine isn’t affecting you, it may be down to a lack of sleep, a natural energy dip, a caffeine tolerance, the caffeine dose, your genetics, or medication.
Written by
Jeff Kahn, M.S., Rise Science Co-Founder
Reviewed by
Jamie Zeitzer, PhD, Rise Science Scientific Reviewer
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Updated Regularly
We regularly update our articles to explain the latest research and shifts in scientific consensus in a simple and actionable way.

Why doesn't caffeine affect me?

  • Caffeine might not affect you because of a lack of sleep, a natural energy dip, a caffeine tolerance, the caffeine dose, your genetics, or medication.
  • If caffeine isn’t giving you the buzz it once did, lower your sleep debt, reset your caffeine tolerance, or increase your caffeine tolerance (only if you drink small amounts of it).
  • The RISE app can improve your energy without relying on caffeine. And 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.

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.


Why Doesn’t Caffeine Affect Me?

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: 

1. You’ve Got a Lot of Sleep Debt

RISE app screenshot showing how much sleep debt you have
The RISE app can work out how much sleep debt you have.

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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2. It’s Your Circadian Rhythm

RISE app screenshot showing your energy peak and dip times
The RISE app can tell you when your energy peaks and dips will be.

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. 

3. You’ve Built Up a Caffeine Tolerance  

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.   

4. You’re Not Consuming Enough Caffeine 

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.” 

5. It’s Your Genetics 

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: 

  • Whether you feel the positive or negative effects of caffeine
  • Your caffeine sensitivity
  • How likely it is to impact your sleep
  • How likely it is to give you anxiety
  • Whether you’ll build up a tolerance for it
  • Whether you’ll develop withdrawal symptoms if you stop consuming it

It also found these responses to caffeine change as you age. 

6. Medications Are Getting in the Way 

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: 

  • Certain antibiotics
  • Heartburn medication 
  • High blood pressure medication
  • Antifungal medication
  • Estrogens and oral contraception
  • Antidepressants
  • Diabetes medication 
  • Medications for psoriasis, eczema, and vitiligo 
  • Stroke medication 

Beyond medication, alcohol can also slow down your caffeine metabolism, changing how it affects you (nicotine, meanwhile, results in increased caffeine clearance). 


What to Do If Caffeine Isn’t Affecting Me?

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. 

Lower Your Sleep Debt 

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: 

  • Take well-timed naps: Naps make you feel more alert immediately (a 10-minute power nap is best for this), but they can also pay back some sleep debt. Just don’t nap too close to bedtime or it’ll disrupt your nighttime sleep. 
  • Go to bed a little earlier: Head to bed a little earlier for a few nights to get in some extra sleep. 
  • Wake up a little later: If you can’t get to bed earlier, lay in later. Just be sure to keep this to one hour maximum so you don’t give yourself social jetlag, disrupting your circadian rhythm. 
  • Maintain good sleep hygiene: If you can’t squeeze in more sleep, focus on your sleep hygiene instead. This is the set of behaviors you can do throughout the day and night to help you fall asleep faster and wake up less frequently at night, therefore increasing how much sleep you get overall. 

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Reset Your Caffeine Tolerance 

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: 

  • Fatigue 
  • Headaches 
  • Depressed mood 
  • Difficulty concentrating 
  • Brain fog 

We’ve covered how long caffeine withdrawal symptoms last here. 

Increase Your Caffeine Consumption (Only If You Consume Small Amounts of It)

RISE app screenshot showing you when to limit caffeine intake
The RISE app can tell you your unique caffeine cutoff time.

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.

How Can I Get More Energy Without Caffeine?

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: 

  • Get some exercise: This increases your heart rate and releases dopamine and serotonin to improve your energy levels and mood.
  • Get some natural light: In the morning, this suppresses the sleep hormone melatonin. Getting outside in natural light is best, but sitting by a window or in front of a light box can also help. During the day, light boosts your serotonin levels, improving your mood. 
  • Take a nap: You’ll feel the immediate boost in alertness as well as pay down sleep debt for long-term energy.  
  • Take a cold shower: This will increase your heart rate, blood pressure, and metabolism for a jolt of energy

We’ve covered more ways to wake yourself up here. 

Get a Natural Energy Boost with RISE 

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.

Your Caffeine Questions Answered:

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