Guide to Caffeine, Caffeine Anhydrous, Dicaffeine Malate, Caffeine Citrate & Pterostilbene
It's been well-established that supplementing with caffeine (also known as 1,3,7-trimethylxanthine or methyltheobromine) prior to a workout can increase mental alertness, power output, anaerobic running capacity and metabolic rate as well as decrease rate of perceived exertion. 
As with most supplements, more caffeine isn't necessarily better; too much caffeine can increase blood pressure, heart rate, cortisol, and anxiety levels. However, when caffeine is used in moderation, it provides a slew of all-natural performance-enhancing benefits with minimal or no side effects.
I'm not going to beat a dead horse and discuss how amazing and beneficial caffeine can be for athletic performance and health reasons. Instead, I'm going to analyze the five most common forms of caffeine:
- Natural Caffeine,
- Caffeine Anhydrous,
- Dicaffeine Malate,
- Caffeine Citrate
At the end of this article you should have a much better idea of what makes caffeine anhydrous different from dicaffeine malate and why you need 200% more caffeine citrate then caffeine anhydrous to achieve the same effects.
Before we start, I want to clear up any confusion on the interpretation of the word "caffeine", when it's listed on the ingredient label. If the label doesn't specify, it could be one or more of the five caffeine types we're going to discuss in this article.
All five types contain the natural occurring xanthine derivate we call "caffeine."  However, some caffeine types are bound to other compounds to change how the body responds to and processes the stimulant.
90% of North American adults consume caffeine on a daily basis; the vast majority of which coming from natural sources like coffee beans, tea leaves, cocoa beans, and guarana berries (although I'm betting most people don't eat the latter on a regular basis). 
Natural caffeine typically achieves peak caffeine blood level concentrations around 40 minutes post-ingestion.  Unlike other sources of caffeine, natural caffeine typically requires steeping a bean or leaf in near-boiling liquid for 3-5 minutes to extract the caffeine. However, the percentage of caffeine extracted depends largely on the temperature of the water, quality of the bean or leaf, and the steeping duration.
One of the drawbacks of using natural caffeine is the lack of consistency in dosing; I could make 100 cups of tea or pots of coffee under near-identical conditions and each time, the caffeine content would vary. However, natural caffeine sources typically include added benefits from phytonutrients like potent antioxidants, vitamins, and minerals. Manufacturers typically process natural caffeine sources to produce the remaining four types of caffeine we will be discussing.
Outside of natural caffeine sources, caffeine anhydrous is the most-used caffeine type in the fitness community. You can find caffeine anhydrous in capsule, tablet, powder, and liquid forms as both a standalone product or as part of the blend in pre-workout and fat-burning supplements.
The main difference between natural caffeine and caffeine anhydrous is water content. Anhydrous literally means "with all water removed."  Manufacturers process natural caffeine sources to create caffeine anhydrous powder, which must be less than 0.5% water by weight. 
The result of this processing and dehydration is the white, bitter, and potent crystalline powder that we all know and love. Standalone caffeine anhydrous supplements can increase caffeine blood levels as quickly as 15 to 45 minutes post-ingestion with levels peaking 60 to 120 minutes post-ingestion.  
Caffeine anhydrous is not only the most popular caffeine type used in supplements, but is also used in the highest quantities relative to other caffeine types.
Per gram, caffeine anhydrous is the cheapest and most highly concentrated form of caffeine.
If you purchase standalone caffeine anhydrous powder or tablets, PROCEED WITH CAUTION. it's extremely easy to consume too much caffeine so start with low doses to determine tolerance and response, then increase as desired. As with any supplement, more isn't always better and can in some cases, more can cause serious health issues.
Some of the most common non-life-threatening side effects include nausea, jitteriness dizziness, diarrhea, and upset stomach.
Supplement manufacturers select caffeine anhydrous to comprise the majority of the caffeine content. If you find that 200-400mg of caffeine per serving causes unwanted side effects, start with a half serving; you'll be doing your body and your wallet a favor.
Dicaffeine malate, also referred to as Infinergy, is an ionic bonded combination of caffeine and malic acid and is trademarked by Creative Compounds LLC.  Although Creative Compounds LLC holds the trademark, it was not the first company to discover and use dicaffeine malate. After cocaine was banned from use in consumer products, Coca-Cola used dicaffeine malate as a replacement stimulant. 
Like other forms of caffeine, dicaffeine malate can increase focus, energy, and metabolism while decreasing perceived fatigue. However, dicaffeine malate offers a unique advantage in that the malic acid supposedly calms the digestive distress commonly caused by natural caffeine and caffeine anhydrous. 
Furthermore, some findings suggest malic acid may weaken the post-ingestion caffeine crash and replenish the energy produced by caffeine. 
There was no significant clinical evidence validating this claim but if it's true, caffeine and malic acid would be a powerhouse combination; one provides energy and the other slows tolerance development. Unfortunately there's no peer-reviewed journal articles on dicaffeine malate so we have to rely on consumer reports, manufacturer claims, and third party websites.
Supplement manufacturers typically include dicaffeine malate as a small percentage of the overall caffeine content.
You've probably heard of caffeine anhydrous and dicaffeine malate, but you may not know about caffeine citrate unless you work in the healthcare or pharmaceutical industries.
This compound, also referred to as CAFCIT®, is a combination of caffeine anhydrous, citric acid monohydrate, and sodium citrate dihydrate.  This combination of compounds does not occur naturally and requires lab synthesis to produce.
Caffeine citrate is commonly prescribed for premature infants, with a gestational age between 28 and 33 weeks, for the short term (10-12 day) treatment of apnea of prematurity.  Apnea of prematurity occurs when a premature infant doesn't breath for 15-20 seconds during sleep.  Caffeine citrate is also commonly prescribed for migraines. 
Caffeine citrate has recently gained popularity in the fitness community because it appears to raise caffeine blood levels faster than other caffeine sources. Whereas caffeine blood levels peak 60 to 120 minutes post-ingestion of caffeine anhydrous, caffeine blood levels peak as quickly as 30 minutes post-ingestion of caffeine-citrate.  
Although caffeine citrate acts faster than caffeine anhydrous, it has one major drawback - 20mg of caffeine citrate provides only 10mg of active caffeine.  This means, milligram per milligram, caffeine citrate provides 50% less caffeine than caffeine anhydrous. We should expect these findings considering caffeine citrate includes two other ingredients whereas caffeine anhydrous does not.
Caffeine citrate may be the ideal stimulant for those looking to increase energy as quickly as possible and are willing to double the dose to do so.
Supplement manufacturers typically include caffeine citrate as a small percentage of the overall caffeine content. Heavier users of caffeine know that 25mg of caffeine anhydrous is next to nothing. However, caffeine citrate, when stacked with other caffeine sources, may be a powerful combination for increasing energy faster and extending the duration of the benefits.
Pterostilbene-CaffeineUnless you follow supplement news and/or read ingredient labels very closely, you've probably never heard of pterostilbene-caffeine.
This compound, also referred to as XCelicorTM or PURENERGY®, is a patent-protected co-crystal combination of caffeine and pterostilbene developed by ChromaDex Inc.  Before we examine manufacturers claims, let's look at pterostilbene as a solo compound.
Pterostilbene (trans-3,5-dimethoxy-4-hydroxystilbene), is a natural compound structurally similar to resveratrol and the primary antioxidant in blueberries.  Studies show that <10mg doses of pterostilbene offer cognitive benefits and 250-500mg doses may reduce cholesterol and blood glucose levels while improving insulin sensitivity. 
Although the research thus far is relatively limited, it appears to offer powerful neuroprotective, cardioprotective, and anticancer properties.  PURENERGY® is approximately 43% caffeine and 57% pTeroPure® pterostilbene by weight.  Compared to traditional (ordinary) caffeine sources, researchers found that PURENERGY® offered the following benefits:  
- 30% higher caffeine levels in the blood during the observation period
- 25% longer half-life and 30% slower absorption rate which led to 45% more caffeine in the bloodstream after 4 hours and 51% more caffeine in the bloodstream after 6 hours
- At 6 hours participants showed less fatigue, greater concentration, alertness, energy, and focus compared to both baseline and traditional caffeine users
Based on the above findings, the manufacturer of PURENERGY® suggests that using pterostilbene-caffeine may decrease the required caffeine content by up to 50% to achieve the same effect as caffeine from traditional sources and may decrease the likelihood of experience the infamous post-caffeine crash. 
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