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As concerns over the safety of energy drinks continue to grow, a study outlines the recent evidence regarding the content, benefits, and risks of the beverages that are popular with adolescents.

The study, published in the journal Pediatrics, reports that more teens are downing energy drinks; in 2003 16% regularly consumed the drinks while in 2008, that percentage jumped to 35%. One study of college student consumption found 50% of students drank at least one to four a month. This year, research documented a jump in energy drink-related emergency room visits and politicians and consumers called upon the Food and Drug Administration (FDA) to look into deaths associated with the drinks.

(MORE: Are Energy Drinks Fatally Caffeinated?)

What do the beverages contain that could pose a health hazard? Currently, the amount of caffeine added to energy drinks is not regulated by the FDA, so often the amounts listed (if they’re listed) are inaccurate. Studies also don’t support all of the claims made by the manufacturers on some of the other ingredients’ ability to maintain energy. The study authors broke down the most common ingredients found in energy drinks: caffeine, guarana, taurine, ginseng, sugars and B vitamins and why they might be problematic.

Caffeine

This is the primary ingredient in energy drinks, and its levels can vary widely. Energy drinks do not fall under the same regulatory category as sodas and often have higher levels of the stimulant than indicated. For comparison, a 6.5 oz cup of coffee contains 80 to 120 mg of caffeine, tea has about 50 mg, and a 12 oz cola cannot have more 65 mg. Energy drinks have significantly higher amounts, with the most well-known brands containing anywhere from 154 mg in a 16 oz Red Bull to 505 mg in a 24 oz Wired X505. There is no official recommended limit for the amount of caffeine a person can consume, but excessive caffeine has been linked to a variety of adverse effects such as high blood pressure, premature birth and possibly sudden death.

Guarana

Also known as Brazilian cocoa, guarana is a plant from South America that contains a caffeine compound called guaranine. One gram of guarana is equal to 40 mg of caffeine. But even if it’s in energy drinks, it’s typically not included in the total caffeine tally. “In reality, when a drink is said to contain caffeine plus guarana, it contains caffeine plus more caffeine,” the authors write. The FDA has not assessed guarana, so it’s risks and benefits remain unknown.

Sugars

The sugar content in energy drinks ranges from 21 g to 34 g per 8 oz, and can come in the form of sucrose, glucose, or high fructose corn syrup. “Users who consume two or three energy drinks could be taking in 120mg to 180 mg of sugar, which is 4 to 6 times the maximum recommended daily intake,” the authors write, noting that adolescents who consume energy drinks could be at risk for obesity and dental problems.

Taurine

As one of the most common amino acids in the body, taurine can support brain development and regulate the body’s mineral and water levels, and could even improve athletic performance. It’s found naturally in meat, seafood and milk. The study authors say the amount of taurine consumed from energy drinks is higher than that in a normal diet. As of yet, there is no evidence this is unhealthy, but there is also no evidence that consuming large amounts is beneficial for the human body.

“Some energy drinks [contain] super-physiologic amounts of these ingredients, embracing the mantra ‘more is better.’ I’m not sure this mantra should necessarily apply,” says study author Dr. Kwabena Blankson, an Air Force pediatrician specializing in teen medicine at Portsmouth Naval Medical Center. “Many energy drink ingredients that are ‘healthy’ are vitamins or minerals you probably get even if you don’t eat the most balanced diet. American foods are heavily fortified. For the average consumer, energy drinks don’t even tell you how much of these special ingredients you are getting, couching the quantities behind the term ‘proprietary blend’ or ‘energy blend.'”

(MORE: 5-Hour Energy Cited In 13 Deaths and ‘Spontaneous Abortion’)

Ginseng

There are claims that ginseng boosts athletic performance, strengthens the immune system and improves mood. But the authors say there is little proof of this, and there isn’t enough ginseng in energy drinks to offer any benefit. The root has also been linked to increased risk of insomnia, headache and hypertension. “Ginseng should be used cautiously, as it can cause undesirable side effects in high doses and may even be dangerous when taken with certain medicines or if the patient is undergoing surgery,” according to the American Cancer Society.

B vitamins and other additives

Studies suggest that B vitamins can improve mood and even fight heart disease and cancer, but the amount contained in each energy drink isn’t enough to have any meaningful effect.

There are also a number of other additives that the authors say need further study. “I was surprised by the profound lack of science supporting the benefit of ingesting some these ingredients such as carnitine, Yohimbe, and bitter orange,” says Blankson. “Adolescent consumers have no idea what these ingredients do. They assume that because they can easily buy it off the shelf that it must be safe for them.” The fact is, however, that there isn’t much scientific evidence on the risks or benefits of these additives—and very little is known about the effects of daily energy drink consumption over the long-term.

The study also highlights the fact that many teens mix their energy drinks with alcohol, which can mask the effects of alcohol and give drinkers the impression they’ve consumed less than they have. Given the lack of knowledge about how energy drinks and alcohol interact, as well as how the beverages mix with medications and antidepressants, the researchers also urge physicians to be aware of energy drink consumption, particularly among teens, and suggest educating patients and parents on the potential consequences of making energy drinks a regular habit.