What is in the drug that makes you sick or dead ? For example ,cocaine is harmful ,but what makes it harmful?
I can’t tell you all about drugs ,but I can 1 you think about them in this 2 way. Your body is a very complicated（复杂的） machine, 3 a lot of chemical machinery, all of which is finally turned 4 it all works together . Special chemicals, which we call drugs ,can affect it in many different ways.
Some drugs are 5 when your body has a problem, as with disease-causing bacteria. Then someone may give you aspirin to keep your temperature from going too 6 or some penicillin（青霉素） 7 it stops the growth of some kinds of bacteria. 8 ,all drugs are really poison, 9 if you take too much ,so you must always use them 10 .
Why do some people take drugs like cocaine ? For a little while they seem to make you feel better ,or happier .But 11 their effects have 12 ,your body has to pay an extra 13 to get back to normal. That makes you want to get 14 of the drug .
Drugs like cocaine have their special effects because they act as 15 for your nervous system. They cut off some of your nerve pathways and take away some of your senses and your 16 .They make you want always more . And just a little too much can even 17 nerves to your heart and stop its beating .
Many of us worry about the 18 around us and what pollution does to us .How about your internal（内在的） environment, and what goes on 19 you ? You control that all by yourself in what you put into your 20 . Most drugs are pollutants .You would not want pollutants in the air and water around you . Why would you want pollutants in your body ?