Is it a sin to smoke weed or use marijuana

The Bible never mentions marijuana by name, so this is a matter of applying its principles rather than quoting a direct verse. Scripture repeatedly warns against anything that clouds sober judgment or masters the mind: 'be not drunk with wine, wherein is excess' (Ephesians 5:18) sets a broader principle of not letting a substance control you, and 'all things are lawful unto me, but I will not be brought under the power of any' (1 Corinthians 6:12) applies directly to anything - alcohol, marijuana, or otherwise - that takes control of the body.

Believers are also called to be sober-minded and self-controlled (1 Peter 5:8; Galatians 5:22-23, self-control as fruit of the Spirit), and to honor the body as 'the temple of the Holy Ghost' (1 Corinthians 6:19-20). Where it is illegal, Romans 13:1 also calls believers to submit to civil law.

Faithful Christians differ on this question since Scripture doesn't name it directly, but the consistent themes are: avoid anything that impairs sober judgment or enslaves you, and let your conscience be shaped by these principles rather than by what is merely permitted.