While there could be some (limited) correlation between drug-abuse and intelligence, there are certainly plenty of less than intelligent individuals who become drug addicted. Perhaps intelligent people survive somewhat longer (as heavy drug abusers), or are able to find innovative ways to support more extreme addictions, but this is also debatable.
Online intelligence tests are most likely bullshit (perhaps there are some truly full length exams, I am not entirely sure). My IQ was somewhat higher as a child, which occurs in some people, while the opposite occurs in other. I had measured my IQ (not online) a few months before I had gotten into drugs, then somewhat recently after a period of heavy drug abuse (opioids and benzos), and noticed a decrease by 6 points, which still probably fits into the standard deviation of the previous score. Nonetheless, my memory is not as sharp as it once was, but it continues to improve to pre-drug levels. One unintended benefit is that I can concentrate a little better now, but this actually makes me a bit uneasy...
Some people forget just how stupid "average" is, so even if true, claims of 120-40 are not surprising. In fact, if you’re able to log-on to a computer, find this website, and type a semi-coherent sentence, I’d wager to say your IQ is at least 115!
This being said, a very high IQ is not synonymous with success (although it can be in regards to academics). The hallmark of a truly intelligent individual is one who is able to get extremely intelligent individuals to work for their purposes.