Explain to me why opioid pain pills are addictive.

[.455_Hunter]

I broke my collarbone in a vehicle accident on November 1st, and had repair surgery four weeks later when it became apparent the bone was going heal problematically. For the first time in my 46 years, after both events, I was prescribed a short regimen of opioid based pain pills. I took the full dose of two 5-mg pills every six hours for 2-3 days, then one pill every six hours for two days, then 1/2 pill every six hours for two days before fully transitioning to OTC acetaminophen. I agree that they helped take the sharp edge off the pain, but made me feel tired and blah, with overly vivid dreams and bad smelling piss. Luckily, my GI tract didn't shut down like some folks experience.

What is the attraction that makes these things supposedly so addictive and dangerous?