Table 2.

Association studies investigating OPRM1 A118G in pain experience and opioid-mediated analgesia

Drug	Method	Finding	Population (number of subjects)	Reference
Morphine	Pain Score and morphine consumption	Reported pain and morphine consumption lowest in AA and highest in GG	Singapore and Han Chinese women receiving morphine for post-cesarean pain (588)	(Sia et al., 2008)
Chronic morphine	Pain Score and morphine consumption	GG required more morphine; no difference in reported pain	Norwegian Caucasians receiving morphine for cancer pain treatment (207)	(Reyes-Gibby et al., 2007)
Chronic morphine	Morphine consumption	GG required more morphine to control pain	Norwegian Caucasians receiving morphine treatment for cancer pain (99)	(Klepstad et al., 2004)
Morphine	Morphine consumption	GG consumed more morphine that AA and AG; no difference in reported pain	Taiwanese patients receiving morphine following arthroplastic knee surgery (147)	(Chou et al,, 2006b)
Morphine	Morphine consumption	G118 required more morphine 24 hours following surgery, but not at 48; no differences in reported pain	Taiwanese female patients receiving morphine following total abdominal hysterectomy (80)	(Chou et al., 2006a)
Morphine	NRS and PPI	G118 were poor responders to morphine treatment	Italian Caucasian patients receiving morphine treatment for cancer pain (145)	(Campa et al., 2008)
Morphine	Morphine consumption	Trend towards an increase in morphine consumption in G118	Mostly Caucasian colorectal surgical patients (74)	(Coulbault et al., 2006)
Morphine or fentanyl	Opioid consumption	GG required more opioid at 24-hr post operation compared to AA and AG	Japanese patients receiving opioid treatment for open abdominal surgery pain (138)	(Hayashida et al., 2008)
Alfentanil	Electrical pain stimulation	GG required higher opioid concentration for pain relief; respiratory depression was not increased with the elevated dose	Healthy German volunteers (20)	(Oertel et al., 2006)
Opioid (Oxycodone, morphine, methadone, fentanyl patch, intrathecal pump)	Pain score (NRS) and evaluation of chronic pain presence x genotype interaction	G118 was less common in members of the chronic pain group; more A118 members were resistant to high-dose opioids.	Mostly Caucasian patients receiving opioid treatment for elecetive laproscopic abdominal surgery (101)	(Janicki et al., 2006)
No drug	Three experimental pain procedures: pressure, thermal, and ischemic	G118 had higher pressure-pain thresholds. Lower thermal pain in G118- allele men, higher in G118-allele women.	Healthy volunteers (mostly Caucasian) (167)	(Fillingim et al., 2005)
Morphine	Pain score and morphine consumption	G118 allele associated with increased pain, increased morphine consumption, but reduced nausea	Women of varying Asian ethnicities receiving voluntary cesarian section (994)	(Tan et al., 2009)