Market research firm Mintel estimates that about 14 percent of new beverages and foods (about 14,000 products) added to store shelves in the past five years contain added or natural caffeine. It’s fine to have a cup or two of coffee to ease into the day, but should you pair it with a spread of caffeinated peanut butter on your morning toast? Caffeine isn’t the health villain it was once believed to be, but getting too much can still have its downsides. We outline some key health-related facts about this ubiquitous compound:

1. Overdoing Caffeine Can Be Dangerous

According to the Department of Agriculture’s latest Dietary Guidelines for Americans, up to 400 mg of caffeine per day—the amount in two to four 8-ounce cups of coffee—can be part of a healthy diet for adults. The Food and Drug Administration says 600 mg per day is too much.

While everyone's tolerance is different, getting more than your normal amount could make you feel nervous, anxious, irritable, jittery, and could cause excessive urine production or irregular heartbeat, says caffeine researcher Maggie Sweeney, Ph.D., postdoctoral research fellow at the behavioral pharmacology research unit at Johns Hopkins University School of Medicine. “That could be the case even for people used to caffeine. And for those who have anxiety or insomnia, it could worsen their symptoms.”

Your caffeine intake can easily add up if you drink coffee and also consume several caffeinated products in a day. For example, if you have a Starbucks coffee in the morning, a water with added caffeine in the afternoon, and a few caffeinated mints during the day, you could easily exceed 600 mg. And at extremely high doses, caffeine can lead to vomiting, convulsions, heart attack, and even death. For instance, in 2014 two young, healthy men died after overdosing on pure, powdered caffeine they bought online. Just 1 teaspoon contains the amount of caffeine in about 28 cups of coffee. That’s a rare example, but it’s a reminder of the potential risks of getting too much caffeine.

2. Where You Get it From Matters

Caffeine is naturally present in the seeds, leaves, and fruit of many plants, including cacao, coffee, and tea. Packaged foods containing ingredients such as coffee and green tea extracts, guarana, kola nut, and yerba mate will add to your daily dose. But synthetic versions of the stimulant may also be infused into food and drink. And though there’s no chemical difference between natural and synthetic caffeine, Sweeney says, the other ingredients in the product may interact with the caffeine. For example, the sugars or the amino acid taurine in many caffeinated energy drinks produce different effects on mood and attention than caffeine alone. And sweet, tasty drinks or foods may cause you to consume too much caffeine without realizing it, Sweeney says.
3. We Still Don’t Know Everything About Caffeine

Caffeine is speedily and completely absorbed through the intestines, so you can get that eye-opening pop in as little as 10 minutes. Once in the brain, it targets and blocks a cascade of neurotransmitter signals that would normally make you sleepy. But it can also have other effects on your body, both positive and negative. Though more research is needed, studies have indicated that caffeine could both precipitate and alleviate headache, boost athletic performance and memory, protect against type 2 diabetes, prevent constipation, and exacerbate menopausal hot flashes.

4. Don't Get All of Your Caffeine in a Single Shot

Pairing a cup of java with caffeinated versions of yogurt and peanut butter at breakfast may sound like a boon, but it may be too much caffeine for you to handle at once. There’s a difference between getting 400 mg of caffeine over the course of a day and consuming that amount or more in one sitting, notes Neal Benowitz, M.D., professor of medicine at University of California, San Francisco. If the drug level rises too quickly in the body, Benowitz says, you'll get a more intense response. To prevent a big punch, Sweeney advises being mindful of your own tolerance. If you start to feel nervous or jittery, you’ve probably had too much.

5. Learning How Much a Product Contains Isn't Easy

Currently, the FDA requires manufacturers to note on the label that a product has added caffeine, but not the amount. And if a product is made with a naturally containing source, such as guarana or cocoa, it will be listed in the ingredients list, but no mention of caffeine on the label is required. The FDA has explicitly approved added caffeine in just one product—colas—but based on that, manufacturers have begun adding caffeine to other foods and beverages. The agency is concerned about the increase in caffeinated products, especially those marketed to kids, and is investigating the potential health consequences of consuming too much caffeine. In December 2015, the FDA asked the makers of Steem caffeinated peanut butter, which had been on the market since 2014, to provide data on the product’s safety. In 2013, Wrigley announced that it would stop production of a line of caffeinated gum after it received questions from the FDA. The maker of Perky Jerky reformulated its caffeinated beef jerkies after the USDA raised concerns in 2010.

But for now caffeinated products are plentiful, and if the trend sticks, you might see more of them on supermarket shelves in the future. To keep your intake in line, check labels and watch out for hidden sources of caffeine.