- A stim-free pre-workout supplement is a pre-workout supplement that doesn’t contain any stimulant ingredients like caffeine, but that still boosts your workout performance.
- Stim-free pre-workouts help you avoid the negative side effects that some people experience when taking caffeine, and increase the effectiveness of regular pre-workout supplements.
- Keep reading to learn how stim-free pre-workouts boost your performance, why you should consider taking one instead of a regular pre-workout, and how to choose the best one.
If you’ve spent any time in a gym in the past decade, you’re probably familiar with the benefits of a good pre-workout supplement.
You know, things like increased strength, endurance, and power, and heightened energy, mood, and focus.
You’re probably also familiar with their downsides—energy crashes, disrupted sleep, jitters, nausea, indigestion, and more.
Even if you haven’t encountered these problems, you’ve probably noticed that your pre-workout supplement has become less effective over time as your body becomes desensitized to caffeine.
All of these issues have given rise to the topic of this article: stim-free pre-workout supplements.
While the idea of taking a stimulant-free pre-workout might seem ridiculous at first blush (aren’t stimulants the whole point?), there are a few reasons you should consider doing so:
- They will boost your workout performance, although not quite as much as pre-workouts containing stimulants.
- They’ll help you avoid many of the negative effects of regular pre-workouts.
- They’ll help you maximize the benefits of regular pre-workouts when cycled properly (keep reading to learn how).
So, if you want to learn more about the benefits of pre-workout supplements, how to choose the best one for you, and how to use them to maximize your performance in the gym, this article is for you.
Let’s start at square one: what the heck is a pre-workout supplement?
Table of Contents
What Is a Pre-Workout Supplement?
A pre-workout is a supplement that’s meant to be taken about 30 to 60 minutes before training to boost your performance. Typically, they contain a mix of ingredients, like caffeine, citrulline malate, and beta-alanine that increase strength, endurance, and focus and reduce fatigue.
You can find all manner of different ingredients in pre-workout supplements from nootropics to branched-chain amino acids (BCAAs) to obscure plant extracts like green coffee bean extract. Most of these ingredients are benign but useless, some are very effective, and some are dangerous.
Read: Everything You Need to Know About Pre-Workout Supplements
The six most scientifically backed (and safe) pre-workout ingredients are:
Many people think that pre-workouts are really just caffeine powder mixed with some sweeteners and flavorings to make it palatable (raw caffeine tastes like the inside of a garbage truck), with the rest of the ingredients acting as a kind of third wheel.
And there’s some truth to this—caffeine delivers most of the benefits you experience from taking a pre-workout supplement. That said, the other five ingredients on the list above aren’t just fillers.
Substances like citrulline, beta-alanine, betaine, and alpha-GPC can also boost athletic performance in subtle but significant ways, and without the downsides of caffeine supplementation.
And that’s where stim-free pre-workout supplements enter the picture.
Summary: A pre-workout is a supplement that’s meant to be taken 30 to 60 minutes before training to boost your performance.
You don't need supplements to build muscle, lose fat, and get healthy. But the right ones can help. Take this quiz to learn which ones are best for you.
Find the Perfect Supplements for You in Just 60 Seconds
You don't need supplements to build muscle, lose fat, and get healthy. But the right ones can help. Take this quiz to learn which ones are best for you.Take the Quiz
What Is a “Stim-Free” Pre-Workout?
A stim-free or stimulant-free pre-workout is a pre-workout supplement that doesn’t contain any stimulatory ingredients like caffeine, but that contains other ingredients that can still boost athletic performance.
The main stimulants you won’t find in stim-free pre-workouts are:
- DMAA (now banned)
So, if stim-free pre-workout supplements don’t contain any stimulants, how do they boost your performance? Several ways:
- Improving your “pump,” positively affecting muscle growth
- Increasing endurance, allowing you to do more sets, reps, or both
- Reducing fatigue, helping you recover faster between sets and lift more weight with better form
- Boosting power output, which is useful for almost any sport
- Decreasing muscle soreness, which helps you have more productive workouts
Thus, although stim-free pre-workout supplements don’t offer the dramatic adrenaline rush you’ll get from the stimulants in regular pre-workout supplements, they can still boost your performance in important ways.
Summary: A stim-free pre-workout is a pre-workout supplement that doesn’t contain any stimulants like caffeine, yohimbine, or theacrine, but that still improves your strength, endurance, power output, and overall athletic performance.
The Top 5 Benefits of Stim-Free Pre-Workout Supplements
If you’re still skeptical of the benefits of a stim-free pre-workout supplement, I understand.
After all, isn’t the whole point of taking a pre-workout to get amped-up so you can train like a man (or woman) possessed?
Isn’t a stim-free pre-workout just a watered down version of a real pre-workout?
And what if you don’t notice any downsides with regular pre-workouts? Will you notice any benefit from taking a stim-free one instead?
Well, yes, no, and yes.
One the one hand, stimulants like caffeine are effective at improving performance in just about any sport you can think of, from powerlifting to cycling, which is why they’re included in so many pre-workout supplements. Thus, stim-free pre-workouts are going to be inherently less effective than regular pre-workout supplements.
On the other hand, regular (stimulant-containing) pre-workout supplements also come with a number of downsides that can outweigh their benefits, especially when used in large amounts for long periods of time.
The main reason to take a stim-free pre-workout supplement, then, is simply to avoid the negative side-effects that often go hand in hand with regular pre-workout supplements. And before you think, “but I don’t experience any negative side effects from stimulants,” research says you probably do, even if you aren’t aware of them.
Note that while I’ve mainly mentioned caffeine in this article, as it’s the most common (and effective) stimulant found in pre-workout supplements, the same principles apply to other stimulants like theacrine and yohimbine.
The five main benefits of stim-free pre-workout supplements are as follows:
- Stim-free pre-workout supplements help you avoid the “pre-workout crash.”
- Stim-free pre-workout supplements help you maximize the benefits of regular pre-workouts.
- Stim-free pre-workout supplements help you avoid nausea, jitters, anxiety, and other unpleasant side effects of stimulants.
- Stim-free pre-workout supplements don’t interfere with your sleep.
- Stim-free pre-workout supplements allow you to get most of your caffeine from other sources.
Let’s go over each point in turn.
Stim-Free Pre-Workout Supplements Help You Avoid the “Pre-Workout Crash”
Caffeine primarily boosts performance by preventing the neurotransmitter adenosine from working as it should (a neurotransmitter is simply a molecule that helps transmit nerve impulses throughout the body).
Adenosine is an inhibitory neurotransmitter, which means it reduces central nervous system (CNS) activity and promotes sleep and restfulness. When adenosine levels are high, CNS activity drops, and when adenosine levels are low, CNS activity increases.
The brain chemistry at play here can get confusing quickly, so just remember this:
- High adenosine = sleepy, sluggish, low-energy
- Low adenosine = alert, focused, high-energy
When you consume large amounts of caffeine, this blocks adenosine from doing its job, boosting alertness, focus, strength, and endurance. That’s the good news.
The bad news is that although caffeine stops the drowsiness-inducing effects of adenosine, it doesn’t stop adenosine production. That is, your body keeps pumping out adenosine even though it’s been “deactivated” by caffeine.
As your body clears the caffeine from your system, though, all of that excess adenosine becomes “reactivated” and floods the brain more intensely than usual. This often leads to a low-energy ennui a few hours after taking caffeine that many people refer to as “pre-workout crash.”
The more caffeine you take, the harsher this crash tends to be. Although I’m not aware of any scientific evidence to prove this, many people also find that taking caffeine in the form of pills or powder tends to produce a more intense crash than getting it from coffee.
Whether or not you experience a pre-workout crash is highly individual. Some people can guzzle a double dose of pre-workout and feel fine, whereas others feel like Eeyore a few hours after taking a single scoop. Most people fall somewhere in between—they notice a slight dip in energy a few hours after a normal dose of caffeine, with larger doses causing increasingly more problems.
One of the main benefits of a stim-free pre-workout supplement is that you don’t have to worry about the pre-workout crash at all.
As Legion’s Director of Research and Development, Kurtis Frank, says, “What the drug giveth, the drug taketh away.” In other words, when you experience a positive effect of a supplement (such as increased energy with caffeine), you often experience its opposite soon after (pre-workout crash).
In the case of a stim-free pre-workout, you won’t get the rush of energy that you’d normally get from caffeine (or other stimulants), but you also don’t have to cope with the comedown, either.
Summary: Many people experience a large drop in energy a few hours after taking a pre-workout containing stimulants, but you won’t experience this with a stim-free pre-workout supplement.
Find the Best Diet for You in Just 60 Seconds
How many calories should you eat? What about "macros?" What foods should you eat? Take our 60-second quiz to get science-based answers to these questions and more.Take the Quiz
Stim-Free Pre-Workout Supplements Help You Maximize the Benefits of Regular Pre-Workouts
An oft-overlooked downside of caffeine (and other stimulants) is that they tend to become less effective over time.
That is, the longer you take caffeine and the more you take, the less it boosts your performance.
This puts you in a pretty wretched catch-22: the more you use caffeine, the less sensitive you become to it, and the less sensitive you become to it, the more you need to use, and the more you need to use, the less sensitive you become, and . . . you get the picture.
What’s more, you also quickly hit a point where no matter how much you increase your caffeine intake, you won’t get the same boost in energy as you used to. This is known as an insurmountable tolerance.
Luckily, there’s a simple way to feel caffeine’s invigorating effects again.
All you have to do is stop using caffeine for a couple of weeks.
After this point, your body will be sensitive to caffeine again, and you should experience the same benefits you did the first time you took it.
The downsides is that in the short-term, you may feel some of the effects of caffeine withdrawal such as decreased performance in the gym. What’s more, if you stop taking your regular pre-workout, you’ll also lose the benefits of the other non-stimulatory ingredients like citrulline, beta-alanine, and betaine.
Unless, that is, you take a stim-free pre-workout supplement.
The logic looks like this:
- Regular pre-workout supplements are more effective than stim-free pre-workout supplements, but they only significantly boost your performance for a few weeks before the effects largely wear off.
- Thus, to maximize the benefits of regular pre-workout supplements, you need to cycle them—taking them for a few weeks before abstaining for a few weeks (a good rule of thumb is two weeks “on” caffeine and one week “off”).
- Stim-free pre-workout supplements act as a stopgap between periods of caffeine abstinence, propping up your performance in the gym while allowing your body to become sensitive to caffeine once again.
For example, you might not have any caffeine during the first two weeks of every month (during which time you’d stick with a stim-free pre-workout), and then switch back to taking a regular pre-workout during the last two weeks of each month.
Or, you could stretch out these phases even longer, alternating between a month of being caffeine-free and a month of consuming moderate amounts of caffeine (including a regular pre-workout supplement).
In either case, by cycling your caffeine intake you’ll get more out of your pre-workout supplement and make faster progress in the gym, and a stim-free pre-workout makes this process easier by boosting your performance when you aren’t taking caffeine.
Summary: In order to maximize the benefits of caffeine (and thus most regular pre-workouts), you need to cycle your intake. Stim-free pre-workout supplements help boost your performance while allowing your body to become sensitive to caffeine once more.
Stim-Free Pre-Workout Supplements Help You Avoid Nausea, Jitters, Anxiety, and Other Unpleasant Side Effects of Stimulants
Aside from the “pre-workout crash,” the caffeine in regular pre-workouts can also cause more immediate negative side effects like nausea, jitters, and anxiety in many people.
Now, it’s worth noting that not everyone responds to stimulants (including caffeine) the same way. Some people are hypersensitive and will experience negative side effects at even the smallest dose (extreme anxiety, nausea, tremors, perspiration, palpitations, restlessness, dizziness, and headaches, followed by a massive crash), while others are much less sensitive and can consume large amounts late in the day without issue.
Most people fall somewhere in between these two extremes. Large and continuous caffeine intake tends to cause unwanted side effects, whereas moderate and intermittent use tends to be well tolerated.
What’s more, many people find these effects tend to get worse over time, which is another reason to cycle your caffeine intake.
Thus, if you’re particularly sensitive to caffeine and don’t like taking large amounts or any, or if you’re currently consuming large amounts and dealing with the fallout, you can give your body a break by taking a stim-free pre-workout supplement.
In other words . . .
If you’re the kind of person who can’t consume any caffeine without negative effects, then you can use a stim-free pre-workout supplement instead indefinitely.
If you’re the kind of person who experiences mild adverse effects from caffeine but still enjoys the energy rush and performance benefits of taking it, you can use a stim-free pre-workout before most of your workouts and a regular pre-workout before your hardest sessions (like when trying to set a new one-rep max).
Summary: If you experience negative side effects from caffeine such as nausea, jitters, and anxiety, you can avoid these issues while still boosting your performance by taking a stim-free pre-workout supplement.
Stim-Free Pre-Workout Supplements Don’t Interfere With Your Sleep
Not getting adequate sleep can wreak havoc on your fitness goals.
For instance, research conducted by scientists at the University of Chicago and National Center of Medicine and Science in Sports shows that insufficient sleep slows down weight loss, increases muscle loss, decreases performance, and reduces testosterone levels.
Basically the polar opposite of what you want if your goal is to get fit.
Caffeine can reduce fatigue and boost wakefulness for seven or more hours (with the exact length of time depending on how fast your body metabolizes caffeine and how much you consume).
For most people, taking a moderate dose of caffeine early in the morning doesn’t disturb their sleep, but taking large amounts and/or taking it late in the day often does. This is particularly problematic for people who train in the late afternoon or early evenings, as taking caffeine any time after mid-afternoon often makes it difficult to fall asleep and can reduce the quality of your sleep after you nod off.
Read: What’s the Best Time of Day to Lift Weights? What 35 Studies Say
Once again, you can avoid this issue by taking a stim-free pre-workout supplement.
You’ll experience many of the same benefits of a regular pre-workout, like improved endurance and power output and reduced fatigue and muscle soreness, but you won’t miss a wink of sleep when you go to bed.
In fact, if you’ve found that taking caffeine in the afternoon or evening interferes with your sleep, you’ll probably progress much faster in the gym by switching to a stim-free pre-workout that lets you get some real Z’s, as high-quality sleep will improve your performance much more than caffeine over the long haul.
Summary: Pre-workouts containing stimulants can interfere with your sleep and thus reduce strength, muscle gain, and workout recovery, but you can avoid this problem by taking a stim-free pre-workout supplement.
Stim-Free Pre-Workout Supplements Allow You to Get Most of Your Caffeine from Other Sources
If you’re an inveterate coffee drinker, like me, regular pre-workouts put you on the horns of a dilemma:
How can you enjoy both your pre-workout supplement and your morning mug of jitter juice without overconsuming caffeine?
One solution is to simply take pre-workout on the days of your hardest workouts and drink coffee on other days (which also makes it hard to effectively cycle your caffeine intake). Another option is to give up coffee and switch to pre-workout (after all, coffee doesn’t give you other performance-boosting ingredients like beta-alanine, citrulline, and so forth). And as a final backstop, you could try decaf. . . .
. . . or not.
Stim-free pre-workout supplements offer a lifeline out of this thorny predicament.
By taking a stim-free pre-workout supplement, you can enjoy your morning cup of coffee . . . while benefiting from the other performance-boosting ingredients in pre-workout supplements . . . and while keeping your caffeine intake at a healthy, sustainable level.
Basically, stim-free pre-workouts give you greater flexibility in how you “spend” your caffeine “budget.”
(And if you’re a tea drinker, all of the same benefits still apply).
Summary: Stim-free pre-workout supplements allow you to keep drinking caffeinated beverages (like coffee), while getting the benefits of a pre-workout supplement, without overconsuming caffeine.
What’s the Best Stim-Free Pre-Workout?
If you’re looking for a 100% natural stim-free pre-workout supplement that improves mood, sharpens mental focus, increases strength and endurance, and reduces fatigue, you want to try Pulse stimulant-free pre workout.
It contains clinically effective doses of four non-stimulant ingredients proven to boost workout performance:
- 8 grams of citrulline malate, which improves muscle endurance, reduces muscle soreness, and improves aerobic performance
- 3.6 grams of beta-alanine, which reduces feelings of fatigue during workouts, and improves anaerobic exercise capacity
- 2.5 grams of betaine, which boosts muscle endurance and increases strength
- 150 milligrams of alpha-GPC, which increases power output
Every ingredient in stim-free Pulse is backed by peer-reviewed scientific research and is included at the same doses used in scientific studies.
Stim-free Pulse is also naturally sweetened and flavored and contains no artificial food dyes, fillers, or other unnecessary junk.
So, if you want to feel focused, tireless, and powerful in your workouts without jitters, nausea, insomnia, or crashes, or you just take a break from caffeine to boost its effectiveness, try stim-free Pulse today.
Some Nutritionists Charge Hundreds of Dollars for This Diet "Hack" . . .
. . . and it's yours for free. Take our 60-second quiz and learn exactly how many calories you should eat, what your "macros" should be, what foods are best for you, and more.Take the Quiz
The Bottom Line on the Best Stim-Free Pre-Workout Supplement
A “stimulant-free,” or “stim-free,” pre-workout is a pre-workout supplement that doesn’t contain any stimulants, but that still improves your strength, endurance, and power output, while reducing fatigue and muscle soreness.
A good stim-free pre-workout supplement can help you:
- Avoid the “pre-workout crash”
- Maximize the benefits of regular pre-workouts
- Avoid nausea, jitters, anxiety, and other unpleasant side effects of stimulants
- Get better sleep
- Get most of your caffeine from other sources
At bottom, stim-free pre-workout supplements help you get many of the benefits of a pre-workout supplement while having greater control over your caffeine intake.
A stim-free pre-workout is a pre-workout supplement that doesn’t contain any stimulants like caffeine, yohimbine, or theacrine, but that still improves your strength, endurance, power output, and overall athletic performance.
And if you’re looking for a 100% natural stim-free pre-workout supplement, try caffeine-free Pulse.
What’s your take on stimulant-free pre-workout? Have anything else to share? Let me know in the comments below!
+ Scientific References
- Ziegenfuss, T., Landis, J., & Hofheins, J. (2008). Acute supplementation with alpha-glycerylphosphorylcholine augments growth hormone response to, and peak force production during, resistance exercise. Journal of the International Society of Sports Nutrition, 5(S1), P15. https://doi.org/10.1186/1550-2783-5-s1-p15
- Lee, E. C., Maresh, C. M., Kraemer, W. J., Yamamoto, L. M., Hatfield, D. L., Bailey, B. L., Armstrong, L. E., Volek, J. S., McDermott, B. P., & Craig, S. A. S. (2010). Ergogenic effects of betaine supplementation on strength and power performance. Journal of the International Society of Sports Nutrition, 7. https://doi.org/10.1186/1550-2783-7-27
- Trepanowski, J. F., Farney, T. M., McCarthy, C. G., Schilling, B. K., Craig, S. A., & Bloomer, R. J. (2011). The effects of chronic betaine supplementation on exercise performance, skeletal muscle oxygen saturation, and associated biochemical parameters in resistance trained men. Journal of Strength and Conditioning Research, 25(12), 3461–3471. https://doi.org/10.1519/JSC.0b013e318217d48d
- Smith, A. E., Walter, A. A., Graef, J. L., Kendall, K. L., Moon, J. R., Lockwood, C. M., Fukuda, D. H., Beck, T. W., Cramer, J. T., & Stout, J. R. (2009). Effects of β-alanine supplementation and high-intensity interval training on endurance performance and body composition in men; a double-blind trial. Journal of the International Society of Sports Nutrition, 6. https://doi.org/10.1186/1550-2783-6-5
- Walter, A. A., Smith, A. E., Kendall, K. L., Stout, J. R., & Cramer, J. T. (2010). Six weeks of high-intensity interval training with and without β-alanine supplementation for improving cardiovascular fitness in women. Journal of Strength and Conditioning Research, 24(5), 1199–1207. https://doi.org/10.1519/JSC.0b013e3181d82f8b
- Sale, C., Saunders, B., Hudson, S., Wise, J. A., Harris, R. C., & Sunderland, C. D. (2011). Effect of β-alanine plus sodium bicarbonate on high-intensity cycling capacity. Medicine and Science in Sports and Exercise, 43(10), 1972–1978. https://doi.org/10.1249/MSS.0b013e3182188501
- Hill, C. A., Harris, R. C., Kim, H. J., Harris, B. D., Sale, C., Boobis, L. H., Kim, C. K., & Wise, J. A. (2007). Influence of β-alanine supplementation on skeletal muscle carnosine concentrations and high intensity cycling capacity. Amino Acids, 32(2), 225–233. https://doi.org/10.1007/s00726-006-0364-4
- Kern, B. D., & Robinson, T. L. (2011). Effects of β-alanine supplementation on performance and body composition in collegiate wrestlers and football players. Journal of Strength and Conditioning Research, 25(7), 1804–1815. https://doi.org/10.1519/JSC.0b013e3181e741cf
- Hoffman, J. R., Ratamess, N. A., Faigenbaum, A. D., Ross, R., Kang, J., Stout, J. R., & Wise, J. A. (2008). Short-duration β-alanine supplementation increases training volume and reduces subjective feelings of fatigue in college football players. Nutrition Research, 28(1), 31–35. https://doi.org/10.1016/j.nutres.2007.11.004
- Stout, J. R., Sue, B. S., Smith, A. E., Hartman, M. J., Cramer, J. T., Beck, T. W., & Harris, R. C. (2008). The effect of beta-alanine supplementation on neuromuscular fatigue in elderly (55-92 Years): A double-blind randomized study. Journal of the International Society of Sports Nutrition, 5. https://doi.org/10.1186/1550-2783-5-21
- Derave, W., Özdemir, M. S., Harris, R. C., Pottier, A., Reyngoudt, H., Koppo, K., Wise, J. A., & Achten, E. (2007). β-Alanine supplementation augments muscle carnosine content and attenuates fatigue during repeated isokinetic contraction bouts in trained sprinters. Journal of Applied Physiology, 103(5), 1736–1743. https://doi.org/10.1152/japplphysiol.00397.2007
- Stout, J. R., Cramer, J. T., Zoeller, R. F., Torok, D., Costa, P., Hoffman, J. R., Harris, R. C., & O’Kroy, J. (2007). Effects of β-alanine supplementation on the onset of neuromuscular fatigue and ventilatory threshold in women. Amino Acids, 32(3), 381–386. https://doi.org/10.1007/s00726-006-0474-z
- Suzuki, T., Morita, M., Kobayashi, Y., & Kamimura, A. (2016). Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study. Journal of the International Society of Sports Nutrition, 13(1). https://doi.org/10.1186/s12970-016-0117-z
- Bendahan, D., Mattei, J. P., Ghattas, B., Confort-Gouny, S., Le Guern, M. E., & Cozzone, P. J. (2002). Citrulline/malate promotes aerobic energy production in human exercising muscle. British Journal of Sports Medicine, 36(4), 282–289. https://doi.org/10.1136/bjsm.36.4.282
- Glenn, J. M., Gray, M., Wethington, L. N., Stone, M. S., Stewart, R. W., & Moyen, N. E. (2017). Acute citrulline malate supplementation improves upper- and lower-body submaximal weightlifting exercise performance in resistance-trained females. European Journal of Nutrition, 56(2), 775–784. https://doi.org/10.1007/s00394-015-1124-6
- Pérez-Guisado, J., & Jakeman, P. M. (2010). Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. Journal of Strength and Conditioning Research, 24(5), 1215–1222. https://doi.org/10.1519/JSC.0b013e3181cb28e0
- Stepanski, E. J., & Wyatt, J. K. (2003). Use of sleep hygiene in the treatment of insomnia. In Sleep Medicine Reviews (Vol. 7, Issue 3, pp. 215–225). W.B. Saunders Ltd. https://doi.org/10.1053/smrv.2001.0246
- Roehrs, T., & Roth, T. (2008). Caffeine: Sleep and daytime sleepiness. In Sleep Medicine Reviews (Vol. 12, Issue 2, pp. 153–162). Sleep Med Rev. https://doi.org/10.1016/j.smrv.2007.07.004
- Boutrel, B., & Koob, G. F. (2004). What keeps us awake: The neuropharmacology of stimulants and wakefulness-promoting medications. In Sleep (Vol. 27, Issue 6, pp. 1181–1194). Associated Professional Sleep Societies,LLC. https://doi.org/10.1093/sleep/27.6.1181
- Souissi, N., Souissi, M., Souissi, H., Chamari, K., Tabka, Z., Dogui, M., & Davenne, D. (2008). Effect of time of day and partial sleep deprivation on short-term, high-power output. Chronobiology International, 25(6), 1062–1076. https://doi.org/10.1080/07420520802551568
- Nedeltcheva, A. V., Kilkus, J. M., Imperial, J., Schoeller, D. A., & Penev, P. D. (2010). Insufficient sleep undermines dietary efforts to reduce adiposity. Annals of Internal Medicine, 153(7), 435–441. https://doi.org/10.7326/0003-4819-153-7-201010050-00006
- Willson, C. (2018). The clinical toxicology of caffeine: A review and case study. In Toxicology Reports (Vol. 5, pp. 1140–1152). Elsevier Inc. https://doi.org/10.1016/j.toxrep.2018.11.002
- Boulenger, J. P., Uhde, T. W., Wolff, E. A., & Post, R. M. (1984). Increased Sensitivity to Caffeine in Patients With Panic Disorders: Preliminary Evidence. Archives of General Psychiatry, 41(11), 1067–1071. https://doi.org/10.1001/archpsyc.1983.01790220057009
- Klein, E., Zohar, J., Geraci, M. F., Murphy, D. L., & Uhde, T. W. (1991). Anxiogenic effects of m-CPP in patients with panic disorder: Comparison to caffeine’s anxiogenic effects. Biological Psychiatry, 30(10), 973–984. https://doi.org/10.1016/0006-3223(91)90119-7
- Coffin, V. L., & Spealman, R. D. (1987). Behavioral and cardiovascular effects of analogs of adenosine in cynomolgus monkeys. Journal of Pharmacology and Experimental Therapeutics, 241(1), 76–83.
- Ishak, W. W., Ugochukwu, C., Bagot, K., Khalili, D., & Zaky, C. (2012). Energy drinks: Psychological effects and impact on well-being and quality of life-A literature review. In Innovations in Clinical Neuroscience (Vol. 9, Issue 1, pp. 25–34). Matrix Medical Communications. www.dietfacts.com
- Fredholm, B. B. (1995). Adenosine, Adenosine Receptors and the Actions of Caffeine. Pharmacology & Toxicology, 76(2), 93–101. https://doi.org/10.1111/j.1600-0773.1995.tb00111.x
- Nehlig, A., Daval, J. L., & Debry, G. (1992). Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects. In Brain Research Reviews (Vol. 17, Issue 2, pp. 139–170). Brain Res Brain Res Rev. https://doi.org/10.1016/0165-0173(92)90012-B
- Dunwiddie, T. V., & Masino, S. A. (2001). The Role and Regulation of Adenosine in the Central Nervous System. Annual Review of Neuroscience, 24(1), 31–55. https://doi.org/10.1146/annurev.neuro.24.1.31
- Daly, J., & Shi, D. (1999). The role of adenosine receptors in the central action of caffeine. In Caffeine and Behavior (Vol. 7, Issue 2, pp. 201–213). CRC Press. https://doi.org/10.1201/9781439822470.ch1
- Warren, G. L., Park, N. D., Maresca, R. D., McKibans, K. I., & Millard-Stafford, M. L. (2010). Effect of caffeine ingestion on muscular strength and endurance: A meta-analysis. Medicine and Science in Sports and Exercise, 42(7), 1375–1387. https://doi.org/10.1249/MSS.0b013e3181cabbd8
- Astrup, A., Toubro, S., Cannon, S., Hein, P., Breum, L., & Madsen, J. (1990). Caffeine: A double-blind, placebo-controlled study of its thermogenic, metabolic, and cardiovascular effects in healthy volunteers. American Journal of Clinical Nutrition, 51(5), 759–767. https://doi.org/10.1093/ajcn/51.5.759
- An, H. J., Choi, H. M., Park, H. S., Han, J. G., Lee, E. H., Park, Y. S., Um, J. Y., Hong, S. H., & Kim, H. M. (2006). Oral administration of hot water extracts of Chlorella vulgaris increases physical stamina in mice. Annals of Nutrition and Metabolism, 50(4), 380–386. https://doi.org/10.1159/000094303
- Kimura, K., Ozeki, M., Juneja, L. R., & Ohira, H. (2007). l-Theanine reduces psychological and physiological stress responses. Biological Psychology, 74(1), 39–45. https://doi.org/10.1016/j.biopsycho.2006.06.006
- Beck, T. W., Housh, T. J., Schmidt, R. J., Johnson, G. O., Housh, D. J., Coburn, J. W., & Malek, M. H. (2006). The acute effects of a caffeine-containing supplement on strength, muscular endurance, and anaerobic capabilities. Journal of Strength and Conditioning Research, 20(3), 506–510. https://doi.org/10.1519/18285.1
- Astorino, T. A., Rohmann, R. L., & Firth, K. (2008). Effect of caffeine ingestion on one-repetition maximum muscular strength. European Journal of Applied Physiology, 102(2), 127–132. https://doi.org/10.1007/s00421-007-0557-x