What are opioid medications used for?

Trying to calm the pain has been one of the most constant searches in the human being. Opioid medications are one method, among others, to achieve this goal.

Although the consumption of opioid drugs has multiplied tenfold in our country in recent years, we are still far below the consumption of other developed countries in the world.

On the other hand, given that the illicit use of opioids is currently important, with consequent personal and societal harm, it is natural that the distinction between these uses and legal employment for analgesia is often confused.

Classification of opioid medications

Opoid plant and medications

We can group opioid drugs according to their way of joining the receptors of their nature. Therefore, we distinguish:

Pure agonists.

Mixed agonist-antagonists.

Partial agonists.

Pure antagonists.

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Pure agonists

Opioid medications that are pure agonists bind directly to μ-type receptors. Due to this interaction, effects of analgesia, euphoria, respiratory depression, constipation, nausea, vomiting and urinary retention are triggered.

That such a variety of effects occur when activating these receptors is an inconvenience when it comes to treating pain with these medications. This is because the desired analgesic effect is accompanied by many undesirable side effects.

The pure agonist prototype opioid is morphine. The higher the dose of this drug, the greater the analgesic effect. However, greater adverse effects also occur.

Heroin is also a potent analgesic but, due to its potent addictive action, it has not been authorized for use in this indication in most countries.

In short, pure agonists are opioid drugs that behave as agonists showing maximum intrinsic activity. Its main indications are to treat different pains such as:


Chronic intense pain resistant to other analgesics.


Transient pain of severe intensity.

Pain associated with myocardial infarction.

Mixed agonist-antagonists

Woman on the couch with pains

In general, agonists are effective in cases of severe pain associated with different pathologies.

This group of opioid medications are nonspecific, which means that they can exert a partial agonist action and even an antagonist. They can interact on the μ receptors, in addition to the κ receptors.

The activation of the κ receptors also produces analgesia, but the action is less than that which occurs with the activation of the μ receptors. The analgesic effect is achieved through the activity of both receptors.


In addition, the set of effects produced by these drugs does not include respiratory depression. However, they also produce a series of undesirable side effects such as hallucinations, anxiety and vomiting, among others.

They can also produce drug dependence, but this is not crossed with the pure agonist drugs of the μ receptors. In this group are, for example, pentazocine, which has a moderate analgesic effect 3 times less powerful than morphine and nalbuphine, among many others.

These drugs have as main indication the treatment of moderate to severe pain.

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Partial agonists

Partial agonist drugs show affinity for opioid receptors with intrinsic activity lower than that of pure agonists. That is why, in the presence of one of the latter can also behave as antagonists.

An example of this group is buprenorphine, which has an analgesic potency 20-30 times greater than morphine. It interacts like several types of receptors what will cause that, if dependence occurs, it will be slower.

The main indications of opioid medications that act as partial agonists, specifically buprenorphine, are:

Treatment of moderate or severe pain.

Pre or post-operative analgesia.

In the management of dependence on other opiates such as heroin.

Pure antagonists

Doctor extracting a drug with a syringe

The antagonists allow reverting the dependence of some drugs used during anesthesia in surgeries.

These drugs are opioids that show an affinity for opioid receptors but lack intrinsic activity. In addition, its affinity extends to the three main types of opioid receptors.

It must be said that, despite having affinity for the three main types of receptors, the affinity for the type μ is greater than for the κ and the δ.

In this group is naloxone, whose main indication is emergency medical treatment to reverse the effects of a known or suspected overdose of opiates that endanger the patient’s life.

Naloxone can also be used after surgery to reverse the effects of opioid medications that are given during the operation. Another indication is injecting newborns to reduce the effects of opiates that the pregnant mother receives before delivery.

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