Recently, a friend of mine was expelled from my school in relation to distribution/utilization of illegal substances within school time. (I'm currently in year nine, and the fact that he is distributing such goods to other school students and adults is outrageous). I was good friends with him through my junior years, and it was in about year seven that his entire personality transformed. He informed me earlier in that year that he was experiencing feelings of depression, and had been influenced by members of online communities he participated to test drugs. He would only ever use it during feelings of extreme depression, and said that it worked as a relaxant and was a good experience. However, the transition into high school signalized the beginning of the end for him. He began taking and testing drugs more frequently, developing addictions. He began to openly discuss his usage of these drugs to our class, and very quickly rumors arose about him. At this point, he developed quite an ego, and began to crave attention, and began to bring Marijuana to school, and utilization on the school ovals after school. He stupidly posted VIDEOS of himself using these drugs on facebook, and was seen by a large portion of the school. His hunger for these substances, and attention, continued to grow, and he began to use LSD during class. He was never caught actually using this, (although I wish he were, at times), but his behavior provoked suspicion in teachers, and began to be watched. It was about this time that he decided to sell these substances for a large profit, and would leave school with HUNDREDS of dollars.
Skip ahead a few days, to one morning, the second last day before end of term. In our school, we have a house system, in which every pupil is divided equally, and a every person in every year level is divided into a tutor group, a group of people from each grade, allowing grades to meet and bond etc. etc. In one of these tutor groups, Jack (my drug-addicted friend) showed someone in his tutor group, one of these substances. A teacher, having the knowledge that he was participating in illegal activities, caught a glimpse of him, and tracked him down as he left to find it in his pocket, and report him to the school principal. He was expelled for possessing these substances. His whole life... His chances at getting a good job... His chances at travelling... Down the drain. For making these mistakes. For abusing these substances. I saw first hand the personality transformations he made, from a bright-eyed, intelligent, hilarious friend to a drug-riddled, attention seeking monster, and as a result of this, would never, ever venture towards trying these substances.
Furthermore, I have tendencies to become extremely addicted to games, as a result of my 'addictive' personality. This quality would increase the effect of the withdrawal symptoms, and create a dependency within me on these substances. Heck, just playing minecraft for a few minutes has led to me playing over 4 weeks just ingame on MCGamer. I'm not stupid enough to risk my wellbeing with potential drug addictions.
So, to conclude, if you have an addictive personality (or not) try to avoid these substances. They can have drastic negative effects on the mind, the body, and those around you.