The main active compound in weed, or marijuana, is delta-9-tetrahydrocannabinol (THC). THC is responsible for the psychoactive effects of marijuana, producing feelings of relaxation, euphoria, altered perception, and potentially influencing mood and cognition. However, it's important to note that marijuana contains many other compounds, including cannabidiol (CBD), which has non-psychoactive properties and is also of interest for its potential therapeutic benefits.