Generally speaking, psychoactive substances such as opium, heroin, cocaine, etc. are so addictive that even experimental use of such drugs can create a grave risk for some persons. To take such a risk (and who knows in advance their own vulnerability) is generally a mortal sin because it opens the way to self-destruction. The gravity of the use of marijuana, which seems not physiologically addictive, is less clear, but it is probable that its habitual use often leads to more serious addictions.
Living the Truth in Love, Fr. Benedict Ashley, OP
Here’s the deal. It’s uncertain that the use of marijuana is not morally wrong. In other words, it’s uncertain that its use is
morally permissible. **But **it is a sin to act without practical certainty that something is
morally permissible. And it is a serious sin to act when there is a real possibility that the action at hand might be seriously wrong.
For example, if I go up to a closed office building and say to myself, “Well, there is
probably no one inside,” and then fill the building with bullet holes using a semi-automatic, I still commit a formal sin of murder, even if no one ends up being killed… nevermind the sins of injustice, scandal, etc. that I also commit.
In a similar way – although the use of marijuana is not possibly as grave as murder – if I smoke marijuana without knowing whether or not it is morally permissible, because competent theologians cannot yet come to a decision on whether it is morally bad, then I cannot act in good conscience. Since there is a real possibility of it being not only slightly morally bad, but seriously morally bad, then to act would be formally a serious sin, even if it turns out, in the end, that marijuana use is not objectively (“materially”) wrong.
Thus, so far as current Catholic moral theology is concerned, the use of marijuana is not permitted.
Moreover, there is also the sin of grave scandal involved if one is an occasion for other persons to go ahead and act against their conscience.
(With that said, the use of marijuana is not
intrinsically wrong, such as contraception is, and so if there is a sufficiently serious reason (such as, for example, very specific circumstantial medical usages for which there is no other substitute), then marijuana could be used. But recreation is not a sufficiently serious reason, and in order to determine what is sufficiently a serious reason, one would need the help of one expertly trained in Catholic moral theology or bioethics.)
Now, as to the OP, you don’t need to know any of that to examine your conscience on the matter. That just concerns future actions. Did you have certainty that what you were doing was permissible, but then only later came to doubt? If that is the case, then there’s no sin, although you might try and set a good example in the future, since you reinforced your friends’ actions. If you have pretty darn goods reasons that some of them trust you on moral matters and would take your advice, then you might encourage them in some way not to do it. This need not necessarily involve words, although it may. Otherwise, no worries, just continue to set a good example. If, on the other hand, you were uncertain that what you were doing was permissible, and you at least in a vague way saw that there is a real possibility of it being seriously wrong, then that’s something which needs to be mentioned in confession. Moreover, you are then really obliged to try and correct the situation to the extent that you damaged it. But if that is not possible, because the others would be unwilling to listen, you are not bound to do that at all.
If you are scrupling over this and are genuinely uncertain as to whether or not you sinned… you are under no obligation to confess. Doubtful mortal sins do not bind you to confess and refrain from Holy Communion. If you do decide to confess a doubtful mortal sin, simply confess it
as doubtful: “Father X., I am doubtful if I committed this sin, but I…”.
However, you might make a perfect act of contrition, by setting aside 10-15 minutes and being contrite for your sins on account of God’s goodness. Perfect acts of contrition are not difficult to make on account of God’s mercy and generosity. In fact, it’s good to get in a habit of making them daily. We can benefit greatly from the immensity of those graces.