In many cases, caffeine interacts with drugs, and other components of coffee also play an important role. Studies have shown that dozens of drugs, including antidepressants, estrogen preparations, and medications for osteoporosis and thyroid disease, are affected by coffee and alter their effects.
A study conducted in 2008 found that if a patient drank coffee shortly before or after taking thyroxine, the drug was absorbed 55 percent less effectively. Other findings also suggest that coffee reduces the body's absorption of the drug alendronate (a bone resorption inhibitor) by 60 percent. In addition, coffee decreases circulating hormone levels, including estrogen, in women.
Oddly enough, some prescription drugs enhance the effects of coffee and coffee drinks. These drugs, which include antidepressants, antibiotics and oral contraceptives, inhibit enzymes, e.g., known to have CYP1A2, i.e., help the body absorb caffeine. As a result, caffeine stays in the body longer than usual. Experiments have shown that for women taking birth control pills, caffeine stays in their bodies for 4 hours longer than others.