It’s usually smart to avoid foods that have long, complicated words on their ingredient labels that make you scratch your head. If the ingredients sound like someone made them up, chances are they did—in a chemistry lab. So it’s not surprising that health professionals have warned against energy drink consumption pretty much since they became popular. Reading the words on a can, you start to wonder: Does anyone really know what’s in this?

The answer is yes, and also not really. We know caffeine and sugar, both of which are plentiful in energy drinks. The other ingredients, though, aren’t quite as ubiquitous in our daily diets—unless you frequent GNC. When it comes to safety, health experts are weary about both the amount of caffeine packed into a single can, and how all the substances may interact.

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“Energy drinks’ caffeine content varies a lot,” Sheri Zidenberg-Cherr, Ph.D., a nutrition specialist in the UC Davis department of nutrition, told SELF.

They’re considered supplements and not a food product, so labeling requirements are quite lax, and the ones that do label caffeine content may not make it very legible. When it comes to the other, more unknown ingredients, Zidenberg-Cherr explained that even if one substance is proven safe on its own, that may change when it’s combined with other things. 

“The problem with these drinks is there are a lot of ingredients being added to them, some that have been used before in this way and others that have not, and it’s the mixture that’s the concern,” Zidenberg-Cherr said.

So what’s even in that mixture? Here are some of the most common energy drink ingredients, and where they rate on usefulness and safety.

1. Ginseng

Used most commonly in Chinese medicine, ginseng is an herb that been used traditionally to treat numerous ailments. It’s generally thought to boost immunity and improve overall health—you’ve probably seen it added to green tea and other herbal remedies. Research doesn’t conclusively back up these claims, but short-term use is thought to be safe. The concern, though, is that it may compound caffeine’s impact and increase side effects like increased heart rate, Zidenberg-Cherr said.

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2. Taurine

“This is an amino acid that we find in protein, meat, fish, breast milk,” Zidenberg-Cherr explains. It helps us maintain neurological function and regulate fluid levels. There are some claims that taking a taurine supplement can improve athletic performance, but not a lot of data exists on its efficacy or its safety as either a supplement or energy drink ingredient.

“The concern has been that when it’s mixed with high amounts of caffeine, there could be effects on the heart,” Zidenberg-Cherr said.

One 2014 review found that taurine seems to counteract some of caffeine’s cardiovascular effects rather than compound them.

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3. Guarana

Guarana is an herb that’s often used as a stimulant in teas, either added or naturally occuring. Its major component is caffeine.

“It has been associated with increased energy and enhancement of physical performance,” Zidenberg-Cherr said.

It’s generally recognized as safe (GRAS), but Zidenberg-Cherr notes that no one really knows if it’s still just as safe when compounded with other high-caffeine ingredients. 

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4. Ginko biloba

This is another herb, added to supposedly increase alertness.

“There’s been a lot of studies looking at it in terms of mental function and mental alertness,” Zidenberg-Cherr said. “But there is not very consistent information on it.”

It’s been used medicinally for thousands of years, according to the Mayo Clinic, and research supports its use for some medical conditions including dementia, anxiety, and schizophrenia. For other uses, evidence is lacking or mixed.

“It might also depend on what other medications someone is taking,” Zidenberg-Cherr added.

Oftentimes, we view herbal ingredients as safe because they’re natural, “but if you’re taking other medications, they could interact with some of these herbs.”

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5. Carnitine

Our bodies naturally produce carnitine, a substance that’s used to turn fat into energy. You can also buy it as a supplement, and it claims to boost exercise performance.

“There’s not much data to encourage its use,” Zidenberg-Cherr said. “There’s no evidence that taking it is going to alter anything, and there’s not a lot of information on its safety as a supplement.”

Some studies suggest carnitine may be promising in treating various health problems, like certain heart conditions, kidney disease, and hyperthyroidism, but in all cases, more research needs to be done and supplements should not be taken without a doctor’s supervision.

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6. Green coffee extract

You may have heard of green coffee bean pills from that lawsuit the FTC won against a company selling them as a magical weight loss drug, with completely falsified “research” to back up their claims. Dr. Oz got some pretty hefty backlash, too, after promoting the bogus pills as a secret weight-loss weapon. Zidenberg-Cherr said green coffee extract, which is often listed in energy drinks and especially those claiming to be all-natural, is just another form of caffeine. 

“People look at it thinking it’s natural so it’s better,” Zidenberg-Cherr said, but all caffeine works the same way in your body. And no, it’s not the magic weight-loss wonder our society has been searching for.