Maybe it would be more properly said: Does marijuana (recreational use) constitute “grave matter”? As we know that for a sin to be mortal it must be: grave matter, done with full knowledge, and willful.
Deliberate drunkenness (with alcohol) is a mortal sin according to St. Thomas Aquinas, because it affects reasoning.
I believe even in small doses marijuana use is “deliberate drunkenness”; and since marijuana use is always deliberate and the affects produced are very similar to drunkenness with alcohol, marijuana use is always a grave matter because of the affects on reasoning.
Marijuana affects the reasoning to such a great extent that the DSM IV classifies being stoned as “Marijuana Psychosis.” Under this DSM description for marijuana use (even if only for several hours) the affects are very similar to schizophrenia. Marijuana distorts the five senses of sight, smell, sound, taste, and touch. It also distorts reasoning in a profound way (even if it is only for two to three hours); it changes the perception of reality. Also people who are stoned are often very paranoid, therefore they have lost a sense of reality. Furthermore under the influence of marijuana it is harder to resist sins of the flesh, due to the affects of loss of reasoning.
Objection #1, One could say,
“Marijuana use doesn’t cause overdoses, cancer, black lung, or emphysema- no one dies from marijuana use.”
Reply to Objection #1:
The reason why deliberate drunkenness is a mortal sin (according to Aquinas) is not because it affects the health, but because it affects reasoning.
Notwithstanding, marijuana use does affect the cardiovascular system; it causes heart problems.
Objection # 2, One could say:
"Marijuana use in small doses, like alcohol use in small doses, is not always drunkenness. Alcohol use only becomes a mortal sin when one looses his/her reasoning abilities of right and wrong.
Reply to Objection # 2:
On the contrary, marijuana use even in small doses drastically affects the use of reasoning. Even in small doses a person is not able to clearly perceive, receive, reflect, and act upon the real (at certain times). This loss of reality leads to a distorted sense of pride.
Short term memory is affected and a person becomes lethargic. The reception of grace which God gives may not always be acted upon properly because reasoning is so distorted. A person doesn’t have to loose completely his/her sense of right and wrong to have this loss of reality and reasoning.
Pot heads can handle marijuana a little more effectively (due to frequent use) however it does change their perception of reality.
Objection # 3, One could say:
“A person can reason better under marijuana use (compared to alcoholic drunkenness), rarely does one see a person get stoned beat up his wife and drive down the street and kill entire family.”
Reply to Objection # 3:
Maybe this is true in this respect, however marijuana use distorts the perception of reality (reasoning). With marijuana a person is not able to clearly perceive, receive, reflect, and act upon the real. This loss of reality (truth) causes pride to be increased.
Furthermore, short term memory is affected. The reception of grace may not always be acted upon properly because reasoning is so distorted.
Objection #4, One could say,
"The affects of being stoned is so slight that a sober person cannot even tell in a conversation, with a person who is stoned, that they are under the influence of marijuana.
Reply to Objection #4:
Reasoning out logical arguments that have never been reasoned before is very difficult to do effectively under the influence of marijuana. Also learning a new task under the influence of marijuana is very difficult. At certain times under the influence of marijuana, fulfilling even the smallest of tasks seems very difficult. With a small amount of alcohol reasoning is not so drastically affected.
Short term memory under the influence of marijuana is very poor. A person cannot even watch a movie, read a book, or have a conversation and remember the events nearly as well as when sober. Even with small doses of marijuana, it seems impossible for reasoning to be effectively done. Furthermore marijuana use leads to lethargy, spiritual sloth.
Also more attention is given to the fleshly nature, and this attention is distorted because it affects the five senses and the mind.
One cannot use the excuse that alcohol drunkenness is not a mortal sin (See link above).
Objection # 5, One could say,
“Marijuana doesn’t cause hang-overs like alcohol and therefore doesn’t affect the behavior the next morning like alcohol.”
Reply to Objection #5:
This I think is one of the reasons why marijuana is a greater evil. Alcohol lends itself naturally to hangovers to discourage alcohol abuse; thus one naturally does not want to be drunk. Since, marijuana use does not lead to hangovers the next day it would lead to greater frequent abuse compared to alcohol.
Objection # 6, One could say,
“It was the Puritans who thought alcohol, tobacco, and caffeine were sinful. Catholics don’t think such substances are evil because matter is not evil, if these substances are done in moderation they are not sinful. Therefore, marijuana should be thought of in similar ways, if done in moderation it is not sinful.”
Reply to Objection #6:
I have already made it clear that Catholics do think deliberate drunkenness is a mortal sin according to St. Thomas Aquinas. Marijuana cannot be thought of like cigarettes or alcohol because it always affects the use of reasoning, even in small amounts.