When inhaled, the active substance ends up in the lungs. There are many blood vessels in the lungs and the drug is quickly absorbed into the blood. The blood is then pumped throughout the body by the heart. This is the fastest way to get a drug into your brain. The drug reaches your brain within 7 to 10 seconds.
Because the effect of smoking is felt so quickly, the user can regulate the intake easily. For example, you stop smoking weed when you feel you are stoned enough.
By inhaling you damage your lungs.
For example: smoking a cigarette or a joint, smoking base coke, inhaling heroin vapors (chasing the dragon), sniffing glue, smoking cannabis through a vaporizer.