Concept:
Self-medication means taking medicines without proper medical advice.
Step 1: Irrational self-medication often involves wrong drug, wrong dose, or incomplete course.
Step 2: Misuse of antibiotics is especially dangerous.
Step 3: It allows microbes to survive and become resistant.
Step 4: Therefore, a major risk is antimicrobial resistance.
\[
\boxed{\text{Antimicrobial resistance}}
\]