Any insight on how to help a friend that's been addicted to drugs and experiencing racing and intrusive thoughts, trouble sleeping, drowsiness & anxiey?

Doctor now. These are withdrawal symptoms and can be life-threatening. Take him to a doctor, hospital, or drug treatment center.
Professional help. This is very serious and requires professional treatment. An intervention by concerned friends and family can help your friend realize they have to get help. Good luck. Most communities have support lines and services as a good place to start.