Which of the following is NOT considered an illegal drug?

Caffeine is not considered an illegal drug because it is a commonly consumed stimulant found in beverages like coffee, tea, and energy drinks. It is legal and widely accepted across many cultures due to its mild effects and social acceptance. In contrast, cannabis and ecstasy are substances that are regulated or prohibited in many countries due to their potential for abuse and health impacts. "Weed" is often a colloquial term for cannabis, which also falls under the category of illegal drugs in jurisdictions where it has not been legalized. Thus, caffeine's legal status distinguishes it from the other substances listed.