If you have a severe caffeine allergy, it can cause anaphylaxis symptoms. Anaphylaxis is a life-threatening allergic reaction that triggers your immune system to release chemicals. Symptoms of anaphylaxis include nausea, a rapid and weak pulse, a drop in blood pressure, and a narrowed airway.

People with a caffeine intolerance metabolize caffeine more slowly than others. When someone with a caffeine intolerance drinks coffee, the immune system sees the caffeine as a harmful substance. As a result, the immune system starts to produce the antibody immunoglobulin E, which causes allergy symptoms such as headaches, anxiety, and skin rash.

There have been some studies that show coffee can reduce the risk of depression, due to its antioxidant and anti-inflammatory properties. Groups who drank coffee reported fewer symptoms of depression than those who didn't consume caffeine.

People with conditions such as inflammatory bowel disease (IBD) and Crohn's may find that coffee causes flare-ups, diarrhea, and nausea.

Different medications can interact with caffeine, increasing its effect on the body. For example, Theo-24 (theophylline), which is used to treat respiratory issues, has been shown to affect how the body processes caffeine. That’s why it’s important to talk to your doctor or pharmacist about any medications you’re taking and your caffeine consumption.