Decriminalization of drugs - in Portugal

This week's issue of The Economist contained an article about a study done in Portugal for the last 8 years. In 2001, Portugal decriminalized drug usage - decriminalized, not legalized - and the study shows that drug usage has gone down and the percentage of users going to rehab has gone up. For the lay person, this is undoubtedly good. What about the gangs that thrive of drug profits? With fewer customers for illegal drugs, what will the gangs turn to for a profit? I think the lack of money may encourage some gang members, or prospective gang members, to go look for a legal job that will probably get them more money than the damaged illegal drug market. But I am still left wondering what the rest will turn to?