Morphine, Oxycodone, Fentanyl (Dosage)

Opioid analgesics are a very useful tool for the treatment of severe pain that does not respond to other treatments. Certain genetic variants can influence the response to these drugs, so knowing this genetic profile can help to provide each patient with the optimal therapeutic dose.

Opioid analgesics (such as morphine, oxycodone, and fentanyl) are also called narcotics. They are only used to treat pain that is intense and is not relieved by other types of analgesics (since these are very potent analgesics). They should not be used for more than 3-4 months, unless the medical profesional gives other indications and lengthens the treatment. Opioids are widely used in the treatment of pain caused by cancer, among other indications.

Its mechanism of action is the binding to opioid receptors in the brain, thus blocking the sensation of pain.

Opioid or narcotic analgesics, taken in excess, can become addictive and are related to deaths due to accidental overdose.


When taking narcotic analgesics or opioids, do not drink alcohol, drive or operate heavy machinery.


Drowsiness, impaired judgment, itching, constipation, nausea, vomiting, withdrawal symptoms when the treatment is stopped (the dose should be gradually reduced over time to avoid the withdrawal syndrome).

Although in our platform we describe the pharmacogenetics of different opioids such as codeine, tramadol, alfentanil and others, in this item we have grouped the genetic polymorphisms that affect the response to morphine, oxycodone and fentanyl in the same way. The genetic information regarding the response to other opioids can also be found in this section of pharmacology but in other different items, since the mediacal literature describes other polymorphisms affecting the response.


  • Morfina: Morfina Braun®, Morfina clorhidrato®, MST Continus®, Oramorph®, Sevredol®, Zomorph®, Dolq®
  • Oxicodona: Oxycontin®, Oxynorm®
  • Fentanilo: Fentanest®

Genes analyzed



Lloyd RA, Hotham E, Hall C, Williams M, Suppiah V. Pharmacogenomics and Patient Treatment Parameters to Opioid Treatment in Chronic Pain: A Focus on Morphine, Oxycodone, Tramadol, and Fentanyl. Pain Med, 2017; 18(12):2369–87.

Lötsch J, von Hentig N, Freynhagen R, Griessinger N, Zimmermann M, Doehring A, et al. Cross-sectional analysis of the influence of currently known pharmacogenetic modulators on opioid therapy in outpatient pain centers. Pharmacogenet Genomics, 2009; 19(6):429–36.

Galvan A, Skorpen F, Klepstad P, Knudsen AK, Fladvad T, Falvella FS, et al. Multiple Loci modulate opioid therapy response for cancer pain. Clin Cancer Res, 2011; 17(13):4581–7.

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