Energy drinks are colorful, sweet, and hugely popular with teens. Now, an important warning for parents. A new Consumer Reports investigation finds what’s inside those drinks may be more than you’re bargaining for.

Energy drinks are everywhere these days. Many of them look like sports hydration drinks and taste like candy. They have flavors like Jolly Rancher flavor and sour gummy worms. It’s so easy just to pop open a cold can and chug it. But inside that can is often a jolt of caffeine that can be far from harmless.

Consumer Reports found that many drinks contain 2 to 3 times the daily caffeine limit recommended for teens: 100 mg. Too much caffeine has been linked to insomnia, anxiety, jitters, and heart-related symptoms, and teens may be especially vulnerable.

To find out exactly what’s in these drinks, Consumer Reports tested 23 popular energy drinks and shots. CR wanted to see how much caffeine is on the label versus how much caffeine is actually in the product.

The results? CR found most drinks came close to or matched their labels, but some had up to 16 percent more caffeine than advertised.

Bang Energy Peach Mango — Label: 300 mg | Tested: 305 mgG Fuel Zero Sugar Energy Drink, Snow Cone — Label: 300 mg | Tested: 297 mgReign Total Body Fuel, Sour Gummy Worm — Label: 300 mg | Tested: 288 mgCelsius Essentials, Fruit Burst Sparkling Fruit Punch — Label: 270 mg | Tested: 272 mgAlani Nu Energy, Cherry Slush — Label: 200 mg | Tested: 215 mgPrime Energy Drink, Ice Pop — Label: 200 mg | Tested: 199 mgAccelerator Zero Sugar, Cherry Ice Pop — Label: 200 mg | Tested: 196 mgBloom Sparkling Energy Drink, Strawberry Watermelon — Label: 180 mg | Tested: 196 mgRedcon1 High Performance Energy, Prime Time Punch — Label: 200 mg | Tested: 187 mgG.O.A.T. Fuel Sports Energy Drink, Watermelon Fruit Punch — Label: 200 mg | Tested: 186 mgVenom Energy Drink, Original — Label: 160 mg | Tested: 163 mgFull Throttle Energy Drink, Original Citrus — Label: 160 mg | Tested: 160 mgZoa Energy Zero Sugar Energy Drink, White Peach — Label: 160 mg | Tested: 158 mgRockstar Energy Drink, Original — Label: 160 mg | Tested: 156 mgMonster Energy Drink, Original Green — Label: 160 mg | Tested: 154 mgNOS High Performance Energy Drink, Original — Label: 160 mg | Tested: 146 mgRed Bull Energy Drink — Label: 80 mg | Tested: 76 mgVitamin Energy Focus+, Tropical Infusion — Label: 260 mg | Tested: 281 mgTweaker Extra Strength, Watermelon — Label: N/A | Tested: 278 mg5-hour Energy Extra Strength, Berry — Label: 230 mg | Tested: 248 mgEternal Energy Grape — Label: 230 mg | Tested: 248 mgBucked Up Buck Shot High Powered Energy Shot, Blue Raz — Label: 200 mg | Tested: 218 mg365 Whole Foods Liquid Energy Shot, Pomegranate — Label: 100 mg | Tested: 116 mg

And the problem doesn’t stop there.

Often, teenagers aren’t just getting caffeine from one source: they’re also getting it from coffee, soda, and even medications. A teenager could wind up with even more caffeine than an adult should have. It’s an additive problem.

The American Beverage Association, an industry trade group, says, “parents should be in the driver’s seat when it comes to what their children have for beverages.”

So, what can parents do? Check labels, track total caffeine from all sources, and pay attention to sleep, because using caffeine to fight fatigue can create a cycle that’s hard to break. The bottom line: when it comes to energy drinks and teens, even one can be too much.

Consumer Reports also recommends that teens learn to read labels, with a reminder that one drink can push them over their daily caffeine limit.