The reason this occurs is because B-12 in combination with certain vitamins and caffeine on some people can act as a vasoconstrictor. What this means is that it tightens up veins and intestines. If you feel your heart really race or feel like blood is just pumping something furious through your body while having these other symptoms it is recommended that you quit taking these medications, and seek medical advice.
Another way that might bring on these symptoms is drinking alcohol(most likely beer or a drink where you have to consume a bunch of liquid). The alcohol will already make your body feel bloated, and your stomach full. This in combination with the extra stomach activity can provide strong discomfort. If this happens it is recommended you stop drinking both liquids, and taken an antacid such as pepto bismol or alka seltzer. If you aren't too wired, it's recommended that you sleep off the effects and take a break from your crazy partying activity.
If you suffer from these symptoms you should at the very least not take energy shots every day. Consider taking them every other day or two days. Another thing to consider is taking your energy shots for a couple days and then taking a two to three day break. This allows the body a break, and you won't build up a tolerance to the energy drink.
Tags: 5 hour energy stomach discomfort, energy shot intestine, energy shot stomach ace