The following 3 page handout is a great introduction to the substance use, abuse and related behaviours unit of the Health strand of the Ontario Curriculum for Grades 6-8.
The handout is organization in this manner:
1) key term definitions
2) explanation and examples/scenarios of legal and illegal substances
3) influences affecting drug use
4) short term and long term effects (definitions and examples)
5) healthy alternatives (making better choices) and support available
Handout is in Word Doc format and can be modified accordingly to suit the various needs (e.g. IEP modifications, accommodations, etc.) of your students.