According to Dr. Jeffrey Stuckert: Chemical changes also occur in the brain as it tries to adapt to overstimulation of the reward pathway. During opioid addiction and opioid dependence, the brain tries to "turn down the volume" and compensate for the vicious highs and lows that occur during repeated opioid use and opioid withdrawal by reducing the number of opioid receptors in the brain. This is what leads to tolerance in people with opioid addiction. More and more opioid is needed to achieve the same effect. The result is that the addict may ultimately feel lifeless, depressed, and unable to enjoy the activities that usually bring him pleasure. By the time most opioid addicts seek treatment, they no longer get the euphoric high from taking an opioid – they only take opioids to function