Introduction

Worldwide estimates of illicit substance use are between 153 and 300 million people (3.4% to 6.6% of the population aged 15-64 years) according to the United Nations Office on Drugs and Crime (UNODC). Cannabis users constitute the largest number of illicit drug users (119-224 million people), followed by users of amfetamine-group substances, opioids, opiates, and cocaine. [1]