CathInfo.com

Lay summary
In contrast to its medical use, the recreational use of marijuana cannot be justified for at least three reasons. First, as scientists have amply docuмented, it harms the organic functioning of the human body. Second, it impedes our ability to reason and in so doing does harm to us. Finally, it has lasting detrimental effects on the user and his neighbor, even when it occurs in a casual setting. Intoxication is always contrary to the integral good of the person. Thus, the use of marijuana is never warranted even for good, non-medical reasons.

I would submit that 100% of these people would be scandalized *just as much* or 99% as much by those same priests/nuns lighting up a regular cigarette. And so...

Can you quote the parts where they specifically address the morality of recreational use of Marijuana?

Since morphine, opium, chloroform and similar drugs can also deprive one of the use of his reason temporarily, that which was said of intoxicating drinks holds also for narcotics.

To use narcotics in small quantities and only occasionally, is a venial sin if done without a sufficient reason. Any proportionately good reason justifies their use, e.g., to calm the nerves, dispel insomnia, etc. Such use becomes gravely sinful if it creates an habitual craving for "dope", which is more difficult to overcome than dipsomania and more injurious to health.