I did not see any place in the article where it was said that JC overdosed on prescription drugs. It also does not say that he attempted suicide. Overdosing is not typically a suicide attempt, but usually accidental.
For him and his girlfriend to both overdose, it sounds to me like they were doing heroin. If it was heroin, its possible that they were not regular users, or they were given a very strong batch, or possibly given a bad batch(meaning spiked with something). An unfamiliar environment will sometimes result in overdose. The body typically builds up a tolerance to drugs, by secreting certain chemicals to counteract the effect of the drugs. One way it does this is through recognition of certain environmental cues that are recognized by the brain as being associated with the drug use. It is my understanding that people overdose in hotel rooms and other unfamiliar surroundings for this reason.
If they were given a bad batch of heroin, and they are regular users, that would be very interesting.