My friend said that it is fine to try illegal drugs as long as you will not continuously use it. This is why he keeps on persuading me to puff some marijuana. However, I told him that a small amount of illicit substance would be very harmful for the body. Besides, it will lead to even bigger problem and greater addiction. I want to convince my friend using factual info, but I am not so sure about the stages of substance use. Can you help me?