This chapter explores the definition of drugs, their interactions with cells, and the concept of therapeutic effects using examples like beta blockers for hypertension. It delves into the distinctions between side effects, adverse effects, and toxic effects, illustrating with examples such as weight loss as an unintended but beneficial effect of a diabetic drug. The dialogue also covers key pharmacological terms like agonist, potency, and dose-response, emphasizing the importance of dosage in determining drug effects.