THe Immediate Effects
A teen's brain is a developing brain.
WHat
Because the teen brain is still developing neuron connections, you will immediately lower your IQ by 8 points the first time by using drugs.
Find Out WhyAddiction
A whopping 30 percent of people who try a drug become addicted the first time, the beginning of a bad path to take. Addiction is when a person had their brain rewired so that they feel a craving for the drug, much like a person would for food.
Dependence
100 Percent of the people who use drugs become dependent on them. This means that they literally can't quite cold turkey or it would kill them, giving them seizures, strokes, etc.
Here's Why...
The teen brain is still developing, specifically in the prefrontal cortex, therefor a teenagers decision making and information processing is still in development. The neurons in the brain are still forming connections. Because of this, if you take a drug like marjuana, which its main component being THC, you will cause the neurons in your brain to stop forming connections, then have major trouble with it. This is because THC is a brain stimulant that the brain makes its self to help form neural pathways. When you take a drug that uses THC, your brain adapts to the situation immediately, and so it stops making THC because it thinks it doesn't have to. The brain stays in this state for some years, and by then you've lost the chance to make those connections.