Those convicted of possessing, using, or trafficking illegal drugs can suffer long jail sentences, large fines and deportation.Now, on with our story...
I'm not using snide remarks based on stereotypes and Korea-bashing to make my point; I'm speaking from a wide range of direct personal involvement.
Let me make this clear for any other would-be pot smoker in Korea. Why you get caught would likely be because someone who knows of your in-country drug use (by smoking with you, by selling it to you, by buying it from you, by getting it from you, by giving it to you, by hearing that you've done it, by seeing you do it, etc.) has fingered you and four other people in order to get a reduced sentence. Think of it as the Korean police version of the Verizon Fave 5.
A reduced sentence will be the ability to plead down to reduced jail time or, if you're lucky, a fine and deportation. If you are arrested and they determine you have drugs in your system, they will pressure you to do the same. If your five and your accuser's five are the same, you're in for some trouble if narcing your way out was the plan.
(I'm guessing a lot of people facing jail time choose to finger their friends and get deported because they assume the people they finger will also avoid jail time by doing the same thing.)
If you are accused, the police will go to your home and/or place of work to question you. I'm not a lawyer and I'm a little fuzzy on this, but from what I piece together from cases I'm familiar with, the police have a right to search your property if you have been fingered like this. If they find drugs, I believe they can formally arrest you at that point.
They may also insist you take a drug test, usually blood or peeing into a cup. I don't know if they take hair samples (hair samples may be legally fuzzy since they can indicate drug use from too early a time period). I'm not sure, but I believe you CAN refuse the test, though I don't know the ramifications. If you don't cooperate, they can, I believe, get immigration involved and you might get deported, though I'm not sure about that part.
All the K-blogs remarks about the Korean legal system notwithstanding, the Korean courts are pretty straightforward and systematic on this stuff: If they don't have evidence against you (drugs found on your person or property, drugs in your system) then they can't charge you. The police might make life hard for you with Immigration or your place of work, and your place of work might decide to let you go, but at least you'd avoid jail time (and if you haven't taken drugs, you should avoid jail time).
If you are a "dealer" then your potential punishment is much more severe, and if the prosecutor is in a bad mood, deportation may not be an option. A "dealer" is anyone who supplies drugs to someone else, including situations where someone says to their buddy, "Hey, wanna light this up when we get home?"
It's McCarthyistic. The goal is not to reduce drug usage, but to eradicate it. Arrest and then imprison or deport those who take it so that they can deter or prevent others. Zero tolerance. If someone is toking up in Korea and they haven't gotten arrested, they've been lucky so far. Maybe only 10% of regular drug users get arrested — I don't know — but is the reward of toking up worth a one-in-ten shot of going to jail or being deported? Maybe some can go ten years or more without getting arrested, but some people get nabbed within weeks or months. It's a crapshoot.