“How do you talk to someone abusing drugs?”

It is great that you care. A very tough task. Best is to gather concerned family members and friends and confront him in an “intervention”. Seek professional help in preparing to do this so you can be most effective.

Take a look at this link for some insight...
https://www.hazeldenbettyford.org/articles/what-can-i-say-to-get-you-to-stop
or
see this Youtube video
https://video.search.yahoo.com/yhs/search;_ylt=AwrEeBwtU2pe3SMAQCgPxQt.;_ylu=X3oDMTByMjB0aG5zBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNzYw--?p=Abusing+Drugs+How+to+talk+to+him&fr=yhs-adk-adk_sbnt&hspart=adk&hsimp=yhs-adk_sbnt&guce_referrer=aHR0cHM6Ly9zZWFyY2gueWFob28uY29tL3locy9zZWFyY2g_aHNwYXJ0PWFkayZoc2ltcD15aHMtYWRrX3NibnQmdHlwZT1BMS1hdGhpLSZwYXJhbTI9OTVjMzc5NzMtZTFjNS00ZjdlLTg0Y2MtOGIxZGYzMDRhZWVmJnBhcmFtMz1zZWFyY2htYW5hZ2VyX35VU35hcHBmb2N1czF-JnBhcmFtND1nLWNjYzEtbHAwLWRzZl9zZWFyY2htYW5hZ2VyLWNwXzE5NzQyOTQ0MzAtYmI5fkNocm9tZX5BYnVzaW5nK0RydWdzK0hvdyt0byt0YWxrK3RvK2hpbX43MTNDRENFNTY3MUVEQTgzQTE0QUY3MzEyQ0YxNUY3QyZwYXJhbTE9MjAyMDAzMDImcD1BYnVzaW5nK0RydWdzK0hvdyt0byt0YWxrK3RvK2hpbQ&guce_referrer_sig=AQAAAMk3ccCySgHsMZtff_qHRNi_loIUKe88vJ5XEcKhyfclVI7ncL_3UThTia3W-xGVxYaKoatMTPml6bXAFUC-5LG5yZr149bIX_lkKPsFMZk3IJfhNKL9eFo6Hp6X4tqMO_nZuekxWq0glzAaMse7I_mSolkq2FQfB9X7tA4ADGdV&_guc_consent_skip=1584026557