There are 3 ways I can see personal drug use creating victims, but drug laws either create or worsen the underlying problems.

First is the most obvious and also the easiest to fix. Person buys drugs, and in the process funds potentially violent criminals and criminal organizations. With a legal, well regulated market this would mostly be a non-issue.

The next would be harm the drug user does to others around them as a result of their drug use. Treating drug addiction as a health issue instead of a criminal one is the only answer.

Finally we have harm to society as a whole by using medical resources to treat the health consequences of long term addictions. Well, rehab costs less than prison and is far more effective at reducing further drug use, since our prisons are chock full of drugs. Furthermore, many recreational drugs are more physically harmful than they should be due to harmful impurities, and overdoses caused by inconsistent or unknown purity.

You're right, it's not victimless. But it shouldn't be a crime, and most of the harm associated with drug use is due to the criminality.