Using drugs can alter the way your mind processes information. On top of that it can actually destroy brain cells and even permanently cause characteristics and symptoms relating to brain damage. Cocaine for example if used for a period of time alters the brain permanently of many of its users. Many former Cocaine addicts have to take anti psychotics for life as a result of the symptoms gained from taking this drug. Some people show strong signs of a learning disability after prolonged usage of heavier substances. Methamphetamine is also a dangerous drug that can destroy ones mind.
Marijuana can relax someone too much. This could result in a poor, or incorrect action during an emergency. The latter could cause for a parenting related mistake that could even bare life threatening consequences. Even the legal and lighter drugs like alcohol and cigarette smoking can have negative effects on health. Doctors prescribe to us different drugs when we need them for specific conditions. That is a valid reason to want to use a drug, however just to get the feeling of high is a dangerous choice to make. Take responsibility and think long term. You only get one brain and if it is functioning it is best to attempt to preserve your brain by taking care of it and avoiding things that harm it.