Heroin is a very powerful drug in the family of Opiates. Opiates do two things, they’re pain killers, and they can also provide a Euphoric feeling, or a High. After a person takes high doses of Opiates for a long period of time, the person can damage their brain. What happens is, the brain makes more Opiate Receptors. The more Opiates a person takes, the more Opiate receptors they make in their brains. That is how tolerance develops. The same dose of Opiates no longer does the same job, so the person must ratchet up the dose. Over a long time, the person ends up on dangerously high doses of Opiates, and then, if they don’t take them, they get sick with severe withdrawal symptoms.