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Test Code OPRM1 Opioid Receptor, Mu 1 (OPRM1) Genotype for Naltrexone Efficacy

Reporting Name

OPRM1 Genotype, Naltrexone Efficacy

Useful For

Identifying individuals with a higher probability of successful treatment for alcoholism with naltrexone

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Whole Blood EDTA

Specimen Required

Multiple whole blood EDTA genotype tests can be performed on a single specimen after a single extraction. See Multiple Whole Blood EDTA Genotype Tests in Special Instructions for a list of tests that can be ordered together.


Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions: Send specimen in original tube.

Specimen Minimum Volume

0.3 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Ambient (preferred)

Reference Values

An interpretive report will be provided.

Day(s) and Time(s) Performed

Tuesday; 8 a.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81479-Unlisted molecular pathology procedure

LOINC Code Information

Test ID Test Order Name Order LOINC Value
OPRM1 OPRM1 Genotype, Naltrexone Efficacy In Process


Result ID Test Result Name Result LOINC Value
31912 OPRM1 Result 82939-0
31913 OPRM1 Interpretation 69047-9
31914 OPRM1 Reviewed by 18771-6

Clinical Information

The mu-opioid receptor (OPRM1) is the primary binding site of action for many opioid drugs and for binding of beta-endorphins. One of the effects of opiate and alcohol use is to increase release of beta-endorphins, which subsequently increases release of dopamine and stimulates cravings. Naltrexone is an opioid antagonist used to treat abuse of opiates, alcohol, and other substances. Naltrexone binds to OPRM1, preventing beta-endorphin binding and subsequently reducing the craving for substances of abuse.(1)


The A355G polymorphism (rs1799971) in exon 1 of the OPRM1 gene (OPRM1) results in an amino acid change, Asn102Asp. Historically, this mutation has been referred to in the literature as 118A->G (Asn40Asp).(2) The G allele leads to loss of the putative N-glycosylation site in the extracellular receptor region, causing a decrease in OPRM1 mRNA and protein levels, but a 3-fold increase in beta-endorphin binding at the receptor.(3) Studies have shown individuals who carry at least 1 G allele have significantly better outcomes with naltrexone therapy including lower rate of relapse (P=0.044), a longer time to return to heavy drinking, and <20% relapse rate after 12 weeks of treatment compared with individuals who are homozygous for the A allele (55% relapse rate).(4) Other studies indicated that 87.1% of G allele carriers had a good clinical outcome, compared with only 54.8% of individuals with the A/A genotype (odds ratio, 5.75; confidence interval, 1.88-17.54).(1) A haplotype-based approach confirmed that the single OPRM1 355A->G locus was predictive of response to naltrexone treatment.(1)


Frequency of the 355G allele varies with ethnicity but ranges between 10% and 40% (European 20%, Asian 40%, African American 10%, and Hispanic 25%).

Analytic Time

1 day

NY State Approved


Method Name

Polymerase Chain Reaction (PCR) 5'-Nuclease End point Allelic Discrimination Analysis


1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. If not ordering electronically, complete, print, and send a Pharmacogenomics Test Request Form (T797) with the specimen (