Caffeine has some proven performance enhancing effects, and its use in competition is legal as long as concentrations in the urine do not exceed a predetermined limit. On the other hand, one could argue that the use of caffeine during races is legal because its performance enhancing effects are negligible. This is also confirmed by a research with amateur cyclists  showing that cycling performance was unaffected by caffeine.
Indeed, despite years of research, exercise scientists and sports medicine professionals are still uncertain of some of caffeine’s effects. There is still a lack of solid dose-response data for caffeine, and there has been a failure to differentiate between acute effects (caffeine’s effects in those who do not normally use it) and chronic effects (caffeine’s effects in those who regularly use it).
Caffeine and Energy
One thing is certain: caffeine doesn't provide energy. Rather it's a stimulant that causes you to utilize the energy that you have from the carbohydrates you have consumed and your muscle glycogen stores. However, the stimulating effect of caffeine diminishes with subsequent doses. That means that you get a big "boost" from your first caffeine shot, and not so much from your 2nd shot, the 3rd shot, etc.
Actually this is exactly the opposite of what you are looking for: in an endurance event you don't want to be utilizing more energy than necessary early in the event as it will help you to run out of juice before the finish line. In fact, especially at the end of an endurance event, you may really be in need of a "boost". If you have been relying on caffeine since the beginning of the event, then you are not going to get the boost you are looking for at the end due to the diminishing stimulating effect. On the other hand, if you have been "caffeine free" for the duration of the event, then you may have a better chance of getting the kick you desire at the end with your first shot of caffeine.
Caffeine and Dehydration
Many studies have shown caffeine to be a diuretic which doesn't surprise most coffee drinkers that have to go take a ‘bio-break’ soon after drinking coffee. A diuretic causes your body to increase urine production, thus potentially contributing to dehydration. In a 2006 study  researchers looked at energy drink consumption and how caffeine and/or other energy drink ingredients like taurine influenced dehydration. They found that the testing group that received the caffeinated energy drinks had significantly more urine output than those that received no caffeine or just taurine only drinks.
Caffeine and Bladder Muscles
A 2011 study  revealed that caffeine promotes early urgency and frequency of urination because caffeine relaxes detrusor muscles, thereby causing the bladder to feel fuller more frequently. The detrusor muscle is a smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to store urine, and contracts during urination to release urine. The detrusor muscle in the bladder helps determine capacity limits of the bladder as well as control bladder output into the urethra. In addition, caffeine causes the bladder to be incapable of holding larger amounts of urine, causing urgency to urinate. This indirectly compounds the diuretic effects of caffeine.
Caffeine and Other Side Effects
Besides diuretic effects some people experience side effects such as gastrointestinal upset, headache, muscle cramps and anxiety. In addition, caffeine has detrimental effects on hand steadiness and possibly reaction time.
Caffeine and Bollox
Ultimately, the above reasons are sufficient to leave caffeine out of our Bollox Energy Gels. With fructose and maltodextrin for higher peak power, a balanced mix of electrolytes and taurine to reduce lactate buildup, Bollox contains all ingredients you need to help you bring more stamina to any endurance event.
Now if you decide to use caffeine anyway to benefit from its alleged performance enhancing effects, avoid routine use of caffeine because you will build a tolerance to many of the effects of caffeine within days. That means no more morning espressos or day-time cappuccinos. And delay consumption to the end of your race or exercise to maximize possible ergogenic effects while minimizing the potential effects of dehydration.