Absorption: The absorption of opioid drugs into the bloodstream depends largely on the user's chosen route of administration of the drug, its dosage, and its lipid solubility. Most NMPOs are taken orally and absorbed into the bloodstream from the walls of the intestine. Some abusers crush and process whole prescription pills into powders that can be smoked, snorted, and injected easily. Alternative routes of administration allow users to combine active NMPO compounds with other drugs to achieve a unique effect and increase drug bioavailability. Specifically, other routes of administration also result in more potent and rapid delivery of the drug to the brain, which often increases the potential for drug abuse (Kollins, 2003; Roset et al., 2001). Studies using nationally representative samples indicate that men use these alternative routes of administration more frequently than women (Back et al., 2011, 2010; Green et al., 2009). Retour et al. reported in 2011 a striking disproportion between men and women in this regard; the majority of men in their sample reported frequently snorting (75%) or injecting (42%) their drugs, while women were much more likely to use oral NMPOs (Back, Lawson et al., 2011).Distribution (reviewed by Gandhi, Aweeka, Greenblatt, & Blaschke, 2004): Many factors affect the distribution of opioid medications throughout the body, including body mass index (BMI), body composition, plasma volume , organ blood flow, and the degree to which a drug binds to tissues and plasma proteins (Atkinson, Huang, Lertora, & Markey, 2012). Women have a higher body fat percentage, lower average body weight, lower average plasma volume, and lower average organ blood flow than men; thus, it...... middle of article......nton, 2010) Most metabolites produced by opioids are inactive or less active than the original compounds and have no clinically relevant pharmacological actions, other opioids such as codeine have metabolites (e.g. morphine) that are at least as potent as the parent drug and can produce analgesic effects as well as adverse effects. Most opioid metabolites are ultimately filtered from the blood via glomerular filtration by the kidneys and excreted through urine. Detection of these metabolites in urine serves as the basis for most drug tests. Patients with kidney failure and other kidney problems may have poor excretion of opioids and other waste products. In addition to renal excretion, glucuronide metabolites can be excreted via bile secretion. Bile flows from the bile duct of the liver into the intestine and is then excreted through the stool..