I think the difference between energy drinks and coffee must have to do with the other herbs and additives in the energy drinks. Although I'm sure there is still some psychological effect as well.
Here's what I found on some of the ingrediants.
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GUARANA
Studies involving guaranį show benefits to cognitive function. They have not been evaluated by the Food and Drug Administration (FDA) or similar government agencies. In the United States, guaranį holds a GRAS-status, i.e. generally regarded as safe and must be labeled as not intended to diagnose, treat, cure or prevent any disease.
A separate 1997 study of guaranį's effects on the physical activity of rats showed increased memory retention and physical endurance when compared with a placebo.
Other studies have shown antioxidant, antibacterial, and fat cell reduction (when combined with conjugated linoleic acid) properties in guaranį
GINSENG
The herbal remedies referred to as "ginseng" are derived from the roots of several plants. One of the most commonly used and researched of the ginsengs is Panax ginseng, also called Asian or Korean ginseng. The main active components of Panax ginseng are ginsenosides, which have been shown to have a variety of beneficial effects, including anti-inflammatory, antioxidant, and anticancer effects. Results of clinical research studies demonstrate that Panax ginseng may improve psychologic function, immune function, and conditions associated with diabetes.
Trials investigating the effects of Panax ginseng on various psychologic parameters have shown positive effects, no effects, or both. In one study of 112 healthy volunteers older than 40 years, the administration of 400 mg per day of the standardized ginseng product Gerimax for eight weeks resulted in better and faster simple reactions and abstract thinking, but no change in concentration, memory, or subjective experience.
The results of two small studies, each including about 30 young, healthy volunteers who received 200 mg of G115 daily for eight weeks, showed improvement in certain psychomotor functions (i.e., better attention, processing, and auditory reaction time), social functioning, and mental health.
GINKGO BILOBA
The extract of the Ginkgo leaves contains flavonoid glycosides and ginkgolides and has been used pharmaceutically. It has many alleged nootropic properties, and is mainly used as memory enhancer and anti-vertigo agent. However, studies differ about its efficacy.
Out of the many conflicting research results, there seem to be basically three effects of Ginkgo extract on the human body: it improves blood flow (including microcirculation in small capillaries) to most tissues and organs; it protects against oxidative cell damage from free radicals (antioxidant); and it blocks many of the effects of PAF (platelet aggregation, blood clotting) that have been related to the development of a number of cardiovascular, renal, respiratory and CNS (Central Nervous System) disorders.
INOSITOL
Inositol, is a cyclic polyalcohol that plays an important role as a second messenger in a cell, in the form of inositol phosphates. It is found in many foods, particularly in cereals with high bran content.
It is classified as a member of the vitamin B complex, though it is not considered a vitamin itself because it can be synthesized by the human body.
Some preliminary results of studies on inositol supplements show promising results for people suffering from problems such as bulimia, panic disorder and bipolar depression.
Inositol has been found in double-blind studies to be an effective treatment for obsessive-compulsive disorder (OCD). It is equal in effectiveness to SSRIs and is virtually free from side effects.
CREATINE
Creatine is a nitrogenous organic acid that naturally occurs in vertebrates and helps to supply energy to muscle cells.
Creatine supplementation has been, and continues to be, investigated as a possible therapeutic approach for the treatment of muscular, neurological and neuromuscular diseases (arthritis, congestive heart failure, disuse atrophy, gyrate atrophy, muscular dystrophy, neuroprotection, etc.).
Two scientific studies have indicated that creatine may be beneficial for neuromuscular disorders. First, a study (Klivenyi et al. 1999) by MDA-funded researcher M. Flint Beal of Cornell University Medical Center demonstrated that creatine was twice as effective as the prescription drug riluzole in extending the lives of mice with the degenerative neural disease amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease). Beal suspects that the neuroprotective effects of creatine in the mouse model of ALS are due either to an increased availability of energy to injured nerve cells or to a blocking of the chemical pathway that leads to cell death.
GLUCURONOLACTONE
Glucuronolactone is a naturally occurring chemical compound produced by the metabolization of glucose in the human liver.
Glucuronolactone has been shown to improve memory retention and concentration as well as acting as an antidepressant and stimulant. It is present in some energy drinks such as Red Rooster, Red Bull, Monster, IRN-BRU 32, Rockstar and Pollen Burst. Most of these drinks contain caffeine, but glucuronolactone is included because it is purported to fight fatigue and provide a sense of well-being.
TAURINE
Taurine is an acidic chemical substance found in high abundance in the tissues of many animals (metazoa), especially sea animals. Taurine is also found in plants, fungi, and some bacterial species, but in far less abundance. Taurine is a derivative of the sulphur-containing (sulfhydryl) amino acid, cysteine. Taurine is present in high concentrations throughout the brain and plays an important role both in neuroprotection and enhancement of neurotransmission.
It is a key ingredient of bile, which in turn is needed for fat digestion, absorption of fat-soluble vitamins as well as the control of cholesterol serum levels in the body. (It is incorporated in the bile acid chenodeoxychloic acid, which emulsify the dietary fats) This nutrient is also used in the proper use of potassium, calcium as well as sodium in the body, and for maintaining cell membrane integrity. It is thought to be helpful with anxiety, hyperactivity, poor brain function and epilepsy as well as hydrating the brain. Taurine, together with zinc is also required for proper eye health and vision.