Regarding one of the topics of this subject: Why can’t painkillers be both safe and effective?
It should be duly noted that,
One of the most problematic conditions when using opioids in clinic is the respiratory depression that they can cause
The most common cause of opioid overdose and death is opioid-induced respiratory depression (OIRD)
essentially due to a neuronal malfunction at the brainstem level
Opioids such as morphine depress the hypoxic ventilatory response in the brainstem by affecting the chemosensitive cells that respond to changes in the partial pressures of carbon dioxide and oxygen in the blood
The difficulty to treat an overdose and the narrow therapeutic window that opioids are known for, make them drugs that need to be monitored very well and thus not much "safe"; although there are a lot being made to counter that effect with the new development of drugs, such as Fentanyl or Remifentanil
Conventional µ receptor opioids have a narrow therapeutic window in part because of their mechanism of action
The opioid receptor desensitization is also a problem, that diminish their effectiveness, being also a cause of dependency and overdose.
Now, regarding your question: Are opioids just dependency inducing or are they actually addictive to a majority of patients?
The answer is both. Opioids are in fact addictive to the majority of patients due to their ability to desensitize quickly.
Opioids are required in ever-increasing doses as you develop a tolerance to them. In other words, the dose you used to take to relive your pain will eventually not work as well, which means you’ll need more of the opioid to get the same effect
From a clinical standpoint, opioid withdrawal is one of the most powerful factors driving opioid dependence and addictive behaviors. Treatment of the patient’s withdrawal symptoms is based on understanding how withdrawal is related to the brain’s adjustment to opioids
From a psychological point of view
Other areas of the brain create a lasting record or memory that associates these good feelings with the circumstances and environment in which they occur. These memories, called conditioned associations, often lead to the craving for drugs when the abuser reencounters those persons, places, or things, and they drive abusers to seek out more drugs in spite of many obstacles
And also they induce dependency essentially with the release of endorphins.
With the definition being stated on the article that you have provided such that Dependence is characterized by the symptoms of tolerance and withdrawal.
One of the brain circuits that is activated by opioids is the mesolimbic (midbrain) reward system. This system generates signals in a part of the brain called the ventral tegmental area (VTA) that result in the release of the chemical dopamine (DA) in another part of the brain, the nucleus accumbens (NAc). This release of DA into the NAc causes feelings of pleasure. Other areas of the brain create a lasting record or memory that associates these good feelings with the circumstances and environment in which they occur.
Two clinically important results of this alteration are opioid tolerance (the need to take higher and higher dosages of drugs to achieve the same opioid effect) and drug dependence (susceptibility to withdrawal symptoms).
By all those reasons chronic pain is thus a very difficult condition to treat and is usually regarded according to the principle of the gate control theory of pain which leads to a broad spectrum analgesia therapy.
Regarding the fact that
If the cause(s) of the chronic pain are removed and the patient is being weaned off the opioids, do the damaging behaviours associated with addiction appear in a large proportion of these patients?
Naturally a high intake for a longer duration is associated with more severe withdrawal and to better grasp this concept there is a psychological scale that enable us to measure that (Clinical Opiate Withdrawal Scale - COWS) by quantifying the severity of opiate withdrawal symptoms,
Patients who score between 5-12 are classified as mild withdrawal, 13-24 as moderate, 25-36 as moderately severe, and over 36 as severe withdrawal
On the other hand, sometimes the chronic use of opioids can lead to brain abnormalities (dependce/addiction abnormalities) and here we have a clear difference about dependence and addiction, because it will lead to different ends.
The abnormalities that produce dependence, well understood by science, appear to resolve after detoxification, within days or weeks after opioid use stops.
The abnormalities that produce addiction, however, are more wide-ranging, complex, and long-lasting. [...] Such abnormalities can produce craving that leads to relapse months or years after the individual is no longer opioid dependent.