What happens to your body when you use heroin?

WATCH ABOVE: A preview for 16×9’s “Heroin for Addicts.”

Even though it creates a “high,” heroin is sometimes called “down” because it’s a depressant, like alcohol. It depresses the central nervous system and the spinal cord. That’s why users feel so relaxed after a hit. The body’s motor functions slow down, the extremities feel heavy, the body gets warm.

What’s happening inside the body is complex. Heroin can be smoked, injected or snorted. With an injection (mainlining) the effect is almost immediate. After only a few seconds, the user feels a rush—a surge of euphoria. That’s the heroin fastening to the brain cells called opioid receptors. These receptors govern how we perceive and react to pain and reward. Our bodies already produce natural feel-good substances call endorphins, but the heroin is more powerful than these endorphins. In effect, the drug hijacks the brain function that makes us feel good and cranks up the pleasure switch. Then the bloodstream distributes the drug, converted into morphine, throughout the body. We feel “better” than we have ever felt as the chemicals do their work. After a few hours, we come back down to the real world. The brain and body return to their natural balance. But we remember the intense feeling, sometimes described as orgasmic.

READ MORE: 16×9: Life at the end of the needle

After repeated use, things change. The body builds up a tolerance to the drug, and you need more heroin in your arm to produce that same initial effect of euphoria. Often, this leads to dependency. If you don’t feed that need, the body rebels. The neurons in the brain that the heroin has suppressed begin pumping out stuff that assaults the central nervous system, and you get nausea, cramps and fever. You are in withdrawal. And that can be awful—a combination of pain and anxiety that, you tell yourself, can only be relieved by one thing . . . more heroin. To borrow a line from Dr. Gabor Mate, you are a point where the drug is the only freedom you know. You are an addict.

16×9’s “Heroin for Addicts” airs this Saturday at 7pm.