What are you really getting when you buy an energy drink?

Some advertisements promise weight loss, increased endurance and even legal highs, but doctors say what they're not advertising are the health and side effects it could have on your body.

"They can usually raise heart rate, blood pressure. They can cause stomach side effects. They can cause anxiety, depression and even headaches," said Dr. Robert Marks.

Comparing the calories, a can of Coke has 35 milligrams of caffeine whereas some energy drinks have 80 milligrams and others skyrocket to 280 milligrams.

It's that extra charge of caffeine that some athletes think will help enhance their performance, but Marks disagrees. "Anytime an athlete drinks an energy drink they are running the risk of becoming seriously dehydrated," Marks said.

Also, instead of helping you to lose weight, Marks said they can actually cause you to gain weight from retaining fluids.

Numerous studies have been done on energy drinks. One that experts say worries them the most is mixing such drinks with alcohol.

"People are twice as likely to harm themselves or others if they were mixing energy drinks with alcohol as opposed to drinking cocktails alone," said Marks.

He said the caffeine, which is a stimulant, reduces symptoms of drunkenness allowing people to drink more and longer.

All of this in mind, it's relevant to note that these drinks are not FDA regulated, so officials do not really know what lasting effects they might have.

Therefore, Marks says "with caffeine intake the key is moderation, if that's considered, people will do OK."