We have an entire government institute that is dedicated to handling drug abuse issues. NIDA is not connected to the DEA in any manner and has much experience and knowledge about addiction, but their expertise is being ignored.
Here, the true experts on addiction give a lengthy explanation of how the brain region leading to addiction is entirely separate from the region that controls dependence and tolerance.
This is a slide show with diagrams to illustrate the points they make. Click on the link of each section to see the slides.
…different parts of the brain are responsible for the addiction and dependence to heroin and opioids.
Review the areas in the brain underlying the addiction to morphine (reward pathway) and those underlying the dependence to morphine (thalamus and brainstem).
Thus, it is possible to be dependent on morphine, without being addicted to morphine.
(Although, if one is addicted, they are most likely dependent as well.) This is especially true for people being treated chronically with morphine for pain, for example associated with terminal cancer.
They may be dependent--if the drug is stopped, they suffer a withdrawal syndrome. But most such patients are not compulsive users of the morphine, and they are not addicted.
However, a proportion of people treated with morphine in the hospital for pain control after surgery may become addicted.
morphine binds to opioid receptors that are concentrated in areas within the reward pathway (including the VTA, nucleus accumbens and cortex).
Morphine also binds to areas involved in the pain pathway (including the thalamus, brainstem and spinal cord).
Binding of morphine to areas in the pain pathway leads to analgesia.
The development of tolerance to the analgesic effects of morphine involves different areas of the brain separate from those in the reward pathway.
Point to the two areas involved here, the thalamus, and the spinal cord (green dots).
Both of these areas are important in sending pain messages and are responsible for the analgesic effects of morphine. The parts of the reward pathway involved in heroin or morphine addiction are shown for comparison.
Dependence develops when the neurons adapt to the repeated drug exposure and only function normally in the presence of the drug.
When the drug is withdrawn, several physiologic reactions occur.
These can be mild (e.g. for caffeine) or even life threatening (e.g. for alcohol). This is known as the withdrawal syndrome. In the case of heroin, withdrawal can be very serious, and the user will seek and take the drug again to avoid the withdrawal syndrome.
The development of dependence to morphine also involves specific areas of the brain, separate from the reward pathway.
In this case, point to the thalamus and the brainstem (green dots). The parts of the reward pathway involved in heroin (morphine) addiction are shown for comparison. Many of the withdrawal symptoms from heroin or morphine are generated when the opioid receptors in the thalamus and brainstem are deprived of the drug.