(WOOD/NEXSTAR) — Maybe you’re among the 90% of U.S. adults who drink caffeinated drinks daily or you like a little pick-me-up every now and then — either way, you know the world’s most popular stimulant definitely can pack a punch. But are you getting too much of it?

While doctors say caffeine usually doesn’t directly lead to health problems, it’s important to be mindful of side effects.

“The (U.S. Department of Agriculture), the (Food and Drug Administration), both of those organizations are going to recommend that 400 milligrams is typically what’s deemed safe for most adults,” said Shanthi Appelö, a registered dietitian with Blue Cross Blue Shield of Michigan.

For reference, Appelö said there’s about 100 mg of caffeine in an 8-ounce cup of coffee — a cup of tea has 50 mg and a 12-ounce cola has 50 mg. Herbal tea doesn’t have caffeine.

Appelö said the half-life of caffeine is four to six hours and some people are more sensitive to it than others.

“After you consume caffeine, half of that caffeine is still going to be present in your system after that time,” Appelö said. And people 65 and older process caffeine at an even slower pace.

In younger people, extreme caffeine like powder caffeine can be dangerous and has been leading to emergency room visits for heart issues.

“If you’re a tea drinker, switching to herbal teas can be a really good idea. It’s also a good idea just to be mindful of how that caffeine racks up throughout the day,” said Appelö.

While caffeine can be used safely, health experts still urge caution if users notice any unwanted side effects like gastrointestinal issues, headaches or difficulty falling asleep. As Princeton University says, users may want to consider pulling back on how much caffeine they’re getting.

How much is 400 milligrams of caffeine exactly?

Mayo Clinic explains that the safe level of 400 milligrams, give or take, amounts to:

• Four cups of coffee
• 10 cans of cola
• 2 energy shot drinks

Meanwhile, Harvard University data shows 16-ounce energy drinks (which are standard size for these types) can pack a 170 mg punch. Even though caffeine contents vary by brand, you’ll want to be extra sure how much you’re consuming when it’s an energy drink.