Opiates can make you throw up—this can even happen to someone given opiates by a doctor—which is why many people don’t like taking them.
Your brain produces its own versions of opiates, called endogenous opioids. These chemicals act just like opiates, binding to opiate receptors. Endogenous opioids help your body control pain. If you’ve ever felt pleasantly relaxed after exercising a lot, that feeling was probably caused by the release of this natural chemical in your brain.