Overconsumption Risks
If you're like most healthy adults, you can safely consume about 200 to 300 mg of caffeine per day, which equals around two to four cups of brewed coffee. You are more likely to experience unwanted effects such as insomnia, nervousness, irritability, upset stomach, muscle tremors and increased heartbeat if you drink more than four cups of coffee a day. You could be more sensitive to coffee's effects, however. You are more likely to experience negative effects with smaller amounts if you aren't used to consuming caffeine, if you have a small body size or if you have an anxiety disorder.
Negative Interactions
You may also be at increased risk of ill effects from coffee if it contains caffeine and you take certain medications or herbal supplements. For instance, certain antibacterial medications can impede caffeine's breakdown and increase the amount of time that its effects linger in your body. Additionally, you may experience heart palpitations, nausea and vomiting if you drink caffeinated coffee in conjunction with a bronchodilator called theophylline. You can reduce your risk of experiencing negative effects if you ask your pharmacist or doctor about whether consuming coffee could influence your medications.