Adverse reactions are unwanted or harmful effects that can occur after taking a medication or receiving a treatment. These reactions can range from mild symptoms, like a rash or headache, to severe issues, such as difficulty breathing or anaphylaxis. It's important for patients to be aware of these potential side effects when using medications, as they can vary from person to person. Healthcare providers monitor adverse reactions closely to ensure patient safety. If someone experiences an adverse reaction, they should report it to their doctor or pharmacist immediately. This helps improve the understanding of how different individuals react to specific drugs, ultimately leading to safer treatments for everyone.