Celiac is definitely a disease. I was diagnosed with it at a very early age. I almost died from stomach issues at age 19 months - had to have emergency surgery to save my life and then subsisted strictly on bananas for the next 4-5 years, as it was the only food I could stomach. My main health problems to this day are still tied to the gut. However, in terms of addiction, the question of whether it is truly a disease is somewhat controversial. The idea of addiction being a disease has only come about since the 1980's. I will admit that I didn't buy it at first, but today i am not so sure. So much of chemical dependency is tied into our chemicals, and when you look at the studies/anectdotal evidence and also the physical Science behind what happens when your body becomes addicted to drugs/alcohol, I must say that I have changed my opinion about this. I truly do think that it is a disease. It goes way beyond willpower or the mental power to just say no. There are other physical processes in play. You are very lucky that you have had some bad experiences that you have seemed to recover from that have shown you the dangers of addiction, but I will say that as someone who has been around so to speak that you have to be very careful regarding the notion of trading one drug for another. I have known a number of people who have "traded" alcohol for marijuana, and to a tee they have come to the conclusion that they are an "addict", regardless of their drug of choice at the time. Marijuana, to most people, is a less dangerous drug then alcohol, but it is still a drug, and people use it for the same reason they use alcohol. So just be very careful.
All my best to you in your travel abroad. I have been lucky enough to travel this great world a number of times and they have all been great experiences.