Since 2001 American troops in combat zones have learned that there are many ways to keep awake and alert when doing that is a matter of life or death. Not all “alertness” cures (coffee, tea, meth, caffeine pills and gum, energy drinks) work the same for everyone. But since 2003, as more American combat troops found themselves operating in tropical climates for long periods one of the favorite methods, caffeine infused “energy drinks” was found to have particularly bad side effects if used a lot in hot weather. Some troops, despite warning about the problem, drank energy drinks instead of water. These drinks do contain a lot of caffeine (100 mg per eight ounce can) but they cause you to sweat and urinate more so you lose more liquids than you take in. There is also the risk of diarrhea. Both dehydration and diarrhea can be incapacitating in combat so by 2012 a growing number of commanders tried to ban energy drinks in the combat zone or at least when troops were going out for extended (24-72 hours) combat operations in hot weather. There was resistance because the troops, especially the younger ones, grew up with these energy drinks. By 2003 the military had informally adopted one brand, “Rip It” because it was the cheapest and just as effective as the more expensive ones. Rip It was available on bases and the military bought it in bulk. But NCOs and junior officers complained about problems (mainly dehydration and diarrhea) that Rip It came to be something of a controlled substance in tropical combat zones.
Rip It thus became the latest mood control drug used by combat troops and all of them have side effects. Not all of them are used for alertness. For example U.S. Navy SEALs often use of sleeping pills (Ambien) while getting ready for operations. That often involves first flying long distances in cargo aircraft, then keeping odd hours in crude accommodations as final preparations are made. All this is quite stressful, making it difficult to fall asleep, even when exhausted. Getting some sleep is essential, so the SEALS are encouraged to take stuff like Ambien if they need it. Many journalists found this shocking. Some even found it disturbing. But taking sleeping pills and stimulants is an ancient tradition. The alternative is getting killed in combat.
The big problem is maintaining alertness in a stressful environment. Once in combat American troops are issued stimulant pills and gum to help them stay alert. Back in 2007 the U.S. Army began issuing "Stay Alert" caffeine gum to combat troops. This was yet another in a long line of drugs troops have been given to keep them alert after long hours in a combat zone. This fatigue problem has existed for a long time and has become particularly acute in the last century or so, as battles became endurance contests, with forces engaged for days on end.
The air force has a similar problem. In the last few decades, as long range bombers and refueling in the air became common, pilots have had to face alertness problems during very long (30 hours or more) missions. In over half a century of using "go pills" (amphetamines), the air force has never had an instance where the stimulant caused a crash or accident. In contrast, over a hundred crashes have been caused by pilot fatigue.
Wakefulness can be a potent weapon, especially for commandos or troops engaged in prolonged combat (like the Battle of Fallujah in 2004). Without these wakefulness drugs you would have to either pull troops out of action so they could rest or leave them in and risk having them make fatal mistakes. Either way you have a problem because there are never enough troops to get the job done. But with the wakefulness medications you can solve the problem, for a few days, anyway.
In Afghanistan and the Middle East the enemy favored even more powerful wakefulness drugs. Many Islamic terrorists consider amphetamines an essential drug for their fighters. Amphetamines have long been used by military personnel to remain alert during combat situations. Islamic terrorists don’t have access to military grade amphetamine pills but instead rely on a commercial product; Captagon. This is the trade name for fenethylline, a synthetic drug that has the same effects as amphetamine but with fewer bad side effects (like increased blood pressure). Fenethylline was still pretty potent and by the 1980s most countries had either outlawed it or made it a prescription drug. Now the most common form of fenethylline is Captagon, which is widely available in the Middle East. Captagon is considered a major problem in the Middle East because there is so much illegal use of it. It is the stimulant of choice among many Syrian rebels, Islamic terrorists and pro-government forces.
Prolonged use of these drugs is not healthy. But neither is being drowsy during combat. It's better to get some sleep when you can, even if you have to take more medications to help make that happen. Troops exposed to prolonged combat find the stimulants lifesavers and consider them as essential as ammunition. Thus the Syrian rebels consider a weapons and ammo shipment incomplete if some Captagon was not included.