What is constructive possession?

Actual possession is straightforward: it was on you. Constructive possession is the theory the State uses when it wasn't.

The elements are knowledge and control. The State must prove you knew of the presence of the substance and had the ability to exercise dominion and control over it. Mere proximity isn't enough on its own.

Where this gets contested is shared spaces — a car with multiple occupants, a shared apartment, a house with visitors. In a jointly occupied space, knowledge and control can't simply be inferred from presence. The State generally needs something more connecting the particular person to the particular substance.

That "something more" is what the case turns on. Statements, fingerprints, DNA, ownership of the container, proximity to that specific location, or conduct suggesting awareness.