Every medicine has a specific molecular job:

• Aspirin permanently blocks the COX enzymes that make prostaglandins, the chemicals behind pain and inflammation
• Antihistamines block histamine receptors, stopping the allergic response that causes sneezing, itching, and swelling
• SSRIs (antidepressants like Prozac) block the reuptake of serotonin, leaving more of it active in the brain
• Beta-blockers block adrenaline receptors on the heart, slowing the heart rate and lowering blood pressure