A monitoring system includes a weight sensor for receiving a vial containing a controlled substance possessed by a patient. A processor receives a weight measured by the weight sensor. A communication circuit transmits the weight measured by the weight sensor to a remote server. The weight sensor may be mounted in a container having a first compartment and a second compartment. The first compartment has a first lid that is releasable without any lock. A second compartment has a second lid that is secured by a lock. The weight sensor is mounted inside the second compartment.