Zach - About.com User
If you're looking for a B-complex vitamin supplement to make you feel more alert or more motivated, you're probably going to be disappointed. Your body needs the B vitamins for many different reasons, including metabolizing food to energy and for healthy brain function, but the B vitamins don't work as fuel, and they don't act like caffeine.
In that case, you're looking for an energy supplement. Typically, these supplements come in the form of tablets or liquids and are easy to find in any store, usually marketed to young people. They contain small amounts of B vitamins and other ingredients like amino acids or herbs, but the main active ingredient is caffeine. Some contain lots of sugar as well.
Dietary supplements may help to ensure that you'll get all the vitamins and minerals you need, but they won't counteract the effects of eating a poor diet. If you're feeling tired and sluggish, you may need to look at foods you eat every day (and you should speak to a health care provider). Be sure to get the right number of calories; avoid excess fats, sugars and sodium; and eat lots of fiber-rich fruits, vegetables and whole grains every day, along with healthy fats, such as omega-3 fatty acids found in fish, flax seeds and canola oil. If you decide you need to take supplements, I've got tips for choosing high quality dietary supplements.
Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Fourth Edition. Belmont, CA. Wadsworth Pub Co. 2005.