Catholic colleges typically have strict policies on alcohol and substances on-campus. That said, they do not necessarily have the same policies across the board. Depending on the specific Catholic college, there may be some tolerance for alcohol, or none at all.
Catholic colleges ensure that their policies on Alcohol and drugs/substances adheres to state and federal laws. Thus, regardless of the specific policies on alcohol at a Catholic college, students under the legal drinking age of 21 are not permitted alcohol consumption, purchase, or possession in any capacity.
Depending on the Catholic college, a dry-campus policy may be in place. A dry-campus is one in which alcohol is not permitted on the premises at all. This means it cannot be sold in the campus stores, offered by any on-campus restaurants or at events, and it cannot be brought onto campus from any outside sources at all. Usually, these policies only extend as far as the campus property, but in some cases colleges expect students to abstain from Alcohol completely during their period of enrollment, even when they are off-campus.
Some Catholic colleges are more tolerant of alcohol and may allow it in certain areas, such as dorms or pre-approved events. Even so, the expectation is that students will use it responsibly, obey state and federal laws, and practice temperance.
As for substance policies, typically all drug substances are banned from Catholic college campuses. Any illegal drug or substance will be banned from a Catholic college, in compliance with state and federal law. Even in states where it is legal, marijuana is still usually banned on Catholic college campuses, with possible exception and extenuating circumstances (prescription & approved medical use). Failure to adhere to these policies will result in disciplinary action, ranging from fines and suspension to expulsion from the university and possible legal action.
As stated, not every Catholic college will have the same policies regarding alcohol and substances. Make sure to understand the restrictions and expectations before arriving on a campus. To find out what specific policies are in place at a Catholic college regarding alcohol and other substances, speak to an admissions officer and check the website of the college(s) you are interested in for the student handbook.