I appreciate this question because it means that there ARE people speaking AGAINST these harmful substances. There are many scriptures which address this matter either directly or indirectly. At the outset, we must realize that there are many of today's issues that the Bible does not SPECIFICALLY mention. The words"marijuana" / COCAINE are not found in the Bible, however there are broader categories and issues in the Bible that DO deal with this subject and we will concentrate on those scriptures.
First of all, despite vehement efforts, marijuana /COCAINE and most other mind-altering drugs are still illegal. As Christians, we are to be subject and submissive to the governing authorities, (Rom. 13:1-5) thus, if something is illegal under our government it is not only unlawful for a Christian, it is also sinful. Even if a person is not a Christian, he or she is still subject to these same laws.
Marijuana/COCAINE along with most other drugs of its kind, has also been proven to have harmful physical and psychological effects on the user. If we believe I Cor. 3:16, we will not do ANYTHING to intentionally harm our bodies, which are the temples of God.
We are also, as Christians, in a constant spiritual battle against Satan (Eph. 6:12). No person goes into battle unprepared, especially Christians. Marijuana/ COCAINE 'S psychological effects include but are not limited to: paranoia, anxiety, fatigue, loss of ambition, lowered inhibitions, loss of concentration, and delusions and hallucinations; not exactly the traits of a godly warrior.
When we realize that Satan is roaming around, seeking to "devour" us (I Pet. 5:8) and that we must be "self-controlled and alert", we must also realize that anything which weakens our resolve or chips away at the armor that God has given us is evil.
I Thess. 5:22 tells us to abstain from the very APPEARANCE of evil. Phil. 4:8 tells us what to think on as Christians and since we usually end up DOING what we think about, this is an excellent scripture for this topic. Finally, Col. 3:5 tells us to put to death whatever belongs to our earthly nature. If we have died to self and live in Christ, we will not allow anything other than God to gain control of our lives. Marijuana / COCAINE WILL take over your life if you let it. I hope I've helped you and I hope you will continue to stand up for what is right.