Drinking a morning cup of coffee can do wonders for your energy level and work productivity, so what’s another cup… and another and another? The boost may seem worth it, but eventually it is doing more harm than good.

At certain levels, coffee may have health benefits. Various studies show it decreases the risk of dementia in older women, protects the brain from other cognitive impairments, aids weight loss and eases headaches, among other applications. It is possible, however, to go overboard.

The Mayo Clinic advises that adults shouldn’t have more than four cups of coffee in a day, or the equivalent of 10 cans of soda or two energy drinks. In terms of caffeine dosage, those four cups of coffee are about 400 milligrams of caffeine. Any more than that and the “heavy caffeine use can cause unpleasant side effects,” it says. Those can include symptoms you may expect from someone who is put on edge — it can cause restlessness, irritability, an upset stomach, a fast heartbeat and nervousness. Other effects of heavy use include insomnia and muscle tremors. And don’t forget the twitches; the National Institutes of Health list caffeine among the most common causes of eye twitches.

The reaction can vary based upon personal tolerance: “How you react to caffeine may be determined in part by how much caffeine you're used to drinking,” the Mayo Clinic says. “People who don't regularly drink caffeine tend to be more sensitive to its negative effects. Other factors may include body mass, age, medication use and health conditions such as anxiety disorders.” Researchers have also suggested that women handle their caffeine better than men.

Part of the issue with reducing intake is that you may be adding caffeine to your body without even knowing it. Certain pain relievers contain caffeine, as do chocolate and many teas. All of these things really add up — “Caffeine is the most widely used drug in the world, consumed by some 80 percent of American adults every day,” the American Psychological Association says.

The safest approach is to pay attention to your body. If you are showing signs of consuming too much caffeine, it’s best to dial it back and see if things improve. But be careful if you’ve become reliant on the stimulant: the Mayo Clinic warns that abruptly decreasing intake can cause withdrawal symptoms like headaches, fatigue and irritability, so it’s best to do it gradually.

“Most often it doesn't pose a health problem,” the organization says. “But be mindful of those situations in which you need to curtail your caffeine habit.”