Opioids look like chemicals in your brain and body that attach to tiny parts on nerve cells called opioid receptors. Scientists have found three types of opioid receptors: mu, delta, and kappa (named after letters in the Greek alphabet). Each of these receptors plays a different role. For example, mu receptors are responsible for opioids’ pleasurable effects and their ability to relieve pain.
Opioids act on many places in the brain and nervous system, including:
- the limbic system, which controls emotions. Here, opioids can create feelings of pleasure, relaxation, and contentment.
- the brainstem, which controls things your body does automatically, like breathing. Here, opioids can slow breathing, stop coughing, and reduce feelings of pain.
- the spinal cord, which receives sensations from the body before sending them to the brain. Here too, opioids decrease feelings of pain, even after serious injuries.
Whether it is a medication like Vicodin or a street drug like heroin, the effects of opioids (and many other drugs) depend on how much you take and how you take them. If they are injected, they act faster and more intensely. If opioids are swallowed as pills, they take longer to reach the brain and are much safer.