This phrase means that you have in your possession a drug that is illegal for sale or use without a prescription. A common misconception is that, in order to be charged with possession of a controlled substance, law enforcement must find the substance on your person. This is not entirely true. To be in possession of a controlled substance, any of the following cases apply. Police or law enforcement find drugs physically on your person. Police or law enforcement find drugs in a place that you have control over. This can include your home, your car, or even your bag. Police or law enforcement find drugs in a space that you share control over with another person, like your home or apartment.