These are the community policies for LINE Webtoons if that's the site you're asking about. https://www.webtoons.com/en/challenge/operationalPolicies
It doesn't really mention drug use, but they do touch upon graphic content which could potentially apply to drug use as well.
" We do not allow graphic depictions of gratuitous violence, or content that promote acts of violence. Examples of prohibited content include:
• Brutal, extended, graphic acts of violence
• Depiction of sadism, or glorification/promotion of inflicting harm on others
• Glorification or promotion of self-harm "