Question: "What does the Bible say about recreational marijuana use?"
Answer: In some parts of the USA, and in many other parts of the world, governments are decriminalizing/legalizing the use of marijuana, not just for medical use, but for recreational purposes as well. Christians’ arguments against marijuana use have traditionally included a submit-to-the-government angle, but, of course, where marijuana is legalized, that aspect is removed from the equation. The question then arises, is it a sin to use marijuana in places where it is legal to do so?
In instances where recreational marijuana use is legal, there are still two primary issues that should keep people from using it. The first is the impact marijuana has on physical health. A recent study by the Journal of Neuroscience demonstrates that even casual marijuana use changes the brain and can lead to mental illness (see http://www.usatoday.com/story/news/nation/2014/04/15/marijuana-brain-changes/7749309/ and http://www.jneurosci.org/content/34/16/5529.abstract"). The fact that children are being hospitalized due to accidental marijuana exposure also demonstrates the health risks: http://www.medicaldaily.com/legalized-marijuana-cookie-sends-2-year-old-girl-hospital-colorado-266338.
The health implications are by no means a secret. And the detailed scientific study demonstrating the effects of marijuana use on the brain was probably unneeded. Simple observation demonstrates that marijuana deadens the brain, resulting in laziness and an inability to concentrate or think clearly. The pain relief many receive from marijuana is a result of this brain-deadening effect. So, very similar to using tobacco and abusing alcohol, the recreational use of marijuana should be avoided due to its adverse effect on health. While the context of 1 Corinthians 6:12–20 is not specifically about harming the body, the clear implication is that we are not to intentionally do things that hurt our bodies.
The second reason to avoid recreational marijuana use is the fact that marijuana is addictive (see http://www.psychologytoday.com/blog/almost-addicted/201311/is-marijuana-addictive and http://www.brown.edu/Student_Services/Health_Services/Health_Education/alcohol,_tobacco,_&_other_drugs/marijuana.php). The Bible commands us not to allow our bodies to become “mastered” by anything. “Everything is permissible for me—but not everything is beneficial. Everything is permissible for me—but I will not be mastered by anything” (1 Corinthians 6:12).
Beyond these two reasons, recreational marijuana use is not consistent with anything the Word of God tells us about the Christian life. We are to be transformed by the renewing of our minds (Romans 12:2), not by the deadening of our minds. We are to be sober-minded about the devil’s schemes (1 Peter 5:8–9), not so stoned that we don’t even care. We are to be filled with the Holy Spirit (Ephesians 5:18), not baked/blasted/wasted by what is undeniably a harmful drug.