No, not necessarily—and in fact if you handle it wisely, it may give you greater credibility with them. They'll realize that you know what you're talking about, and that you know the dangers of drugs from firsthand experience.
This doesn't mean it was a good idea for you to experiment with drugs when you were younger, and you need to make this clear to your children. In other words, they need to realize that they don't actually have to experiment with something in order to learn if it is harmful. One of the marks of a mature person is that he or she learns from the experiences of others. One of your goals should be to teach this truth to your children.
The most important thing you can do, however, is to make Christ the center of your home and your family, and to show your children the importance of putting Him first in their lives. God loves them (just as He loves you), and He doesn't want them to ruin their lives or follow the wrong path in life.
If you've never done so, ask Christ to come in to your lives today—and then urge your children to give their lives to Him as well. Young people today face enormous pressures that can easily destroy them—but with Christ's help they can resist them. The Bible says, "Put on the full armor of God so that you can take your stand against the devil's schemes" (Ephesians 6:11).