On December 14, 1999, Shin Dong Yup got arrested for smoking marijuana. This is a rumor behind this scandal:
Shin Dong Yup was in a relationship with a very popular model Lee Sora at that time. Lee Sora filmed a porno for money when she debuted and it was exported overseas. Unfortunately, a sports journalist found the tape when he was travelling aboard, and he was going to report it as soon as he returned to Korea.
Shin Dong Yup heard the news before it was reported. He requested a meeting to see the journalist and asked him not to report it. The journalist refused to do his favor because it would be very big news. Shin Dong Yup made a promise - that he will smoke marijuana so that the journalist could report his marijuana news instead...
Soon after, the journalist did report big news - "Shin Dong Yup marijuana scandal". Shin Dong Yup was immediately thrown into a jail. However, as soon as he was discharged, he was cast in a big show as an MC, which was a rare case. Psy had to reflect for 2 years, Lee Tae Ran for 1 year... Shin Dong Yup's comeback was a very rare case. It's because the PDs knew that he smoked marijuana for Lee Sora and they did a petition to support him. However, Lee Sora broke up with him shortly after he was discharged.
But also keep in mind that there isn't any credible sources for this rumor. A lot of K-netizens take this rumor as an open secret, but at the same time, many netizens also claim that this rumor has no evidence or credibility. Whenever this rumor is brought up, K-netizens argue over the truth of this rumor. For example, in a recent article of criminal celebrities, the top comment was talking about this rumor. I'm going to post one of the replies to the comment:
[+4, -1] Do you really think this rumor is credible??? I'm so dumbfounded... Do you take Lee Sora as a joke just because she doesn't sue the rumor makers? Hey, don't you guys know how trashy the entertainment journalists are? If this rumor was true, then the journalists would've found the tape and reported it already. Shin Dong Yup is just a criminal who smoked marijuana. When Shin Dong Yup's scandal was being reported, Lee Sora was the MC of Hanbam... It was a tragedy... Do you really believe the rumor made up by Shin Dong Yup fans? So pathetic, geez. Think objectively instead of making up stuff.
We should take this rumor with a grain of salt