Step 1: Understanding the Concept:
This is a factual question asking for the specific date of an international observance designated by the United Nations.
Step 2: Detailed Explanation:
The International Day against Drug Abuse and Illicit Trafficking is observed annually on 26th June.
This day was designated by the United Nations General Assembly in December 1987. The date was chosen to commemorate Lin Zexu's dismantling of the opium trade in Humen, Guangdong, just before the First Opium War in China. The day aims to raise awareness about the major problem that illicit drugs represent to society.
Step 3: Final Answer:
The International Day against Drug Abuse and Illicit Trafficking is observed on 26th June.