An opioid agonist drug binds to opioid receptors in the human body and triggers the receptors to send a signal. The signal it sends is comparable to what it would be if the receptors were triggered by morphine.
Drugs classified as opioid agonists include codeine, heroin, hydrocodone, hydromorphone, morphine, oxycodone, oxymorphone, along with many other drugs that are marketed as narcotic pain relievers.
An opioid antagonist drug does the opposite, it binds to opioid receptors in the human body and severely reduces or blocks the signal the receptors send. Opioid antagonists include drugs like nalmefene, naloxone, naltrexone.
If you had a history of opioid consumption but decided to quit, an opioid antagonist can be utilized to prevent you from starting to use again. Since antagonists severely reduce or block the pleasant effects, there is little reason to take an opioid agonist.
Opioid antagonists can cause instant withdrawal for people that take opioid agonists (heroin, oxycodone, etcetera). For this reason they should only be started after a period of abstinence, or withdrawal will be an even worse experience than it usually is.
In order to comply with federal recommendations regarding opioid addiction, some US medical practitioners are trying to do so by getting people who are taking opioids for pain relief into switching to opioid antagonist and partial antagonists.
Some partial antagonists will produce mild analgesia (pain relief) or euphoria for people with no tolerance to opioids. However, for those who have a previous history of consuming opioids, the effects will be limited in comparison.
Partial antagonists like buprenorphine might be good if you are trying to quit doing heroin, oxycodone, or another addictive opioid. They produce some amount of the positive effect of agonists.
This might make withdrawal easier, while blocking most of the positive properties of opioid agonists. So there is limited benefit to taking heroin, oxycodone, or other agonist while taking a partial antagonist.
In conclusion, if you are taking any type of opioid for medical, recreational, spiritual, or any other purpose, opioid agonist drugs are the good ones. Avoid opioid antagonist drugs at all cost, unless you have a very good reason to do so.
--- Opioid agonists reduce pain and produce pleasant effects.
--- Opioid antagonists prevent the pain relief and pleasant effects.
--- Opioid antagonists can also block the effects of endorphins.
--- Opioid partial antagonists can help quitting opioids.
Low dose naltrexone (an opioid antagonist) can be effective for treating chronic pain and several other maladies. It doesn't work for everyone but might be worth a try, especially if you have no history of daily opioid consumption.