Almost all foods interact with the brain in different ways. The western diet has a number of foods that strongly predispose someone to enjoy certain drugs more.
One study has showed administering an opioid antagonist over time will make the effects of an opioid drug more pronounced. Common food products like milk contain those types of chemicals. Milk has a fraction of its constitutes called kappa casein that antagonize opioid receptors.
Unlike some other receptors, opioid receptor antagonists don't upregulate mRNA, they alter the receptor to make it easier to activate. This property makes opioid receptor activation easier to get addicted to because agonists down regulate the mRNA.
|Flickr @ shilohtd|
Chronic caffeine increases the effects of nicotine.  Nicotine increases the effects of cocaine. One of these chemicals could lead to a greater chance of addiction of another.
Jobs are necessary in the society we are in now, But working long hard hours is not quite a good thing for dopamine in the long run. People who work hard at work seem to get a dopamine rush which can in turn lead to lowered levels of dopamine.
|Flickr @ Travis Isaac|
Lowered dopamine levels will thus lead to drug use (and alcohol). A study supports this idea " we find evidence that for working men characteristics of jobs affect levels of alcohol consumption and the incidence of self-medicating drinking." 
Stress (at jobs) causes an uprise in DHT. Studies show that this hormone even causes mice brains to crave alcohol (suggesting any drug too).
School's summers, work's vacations, and the weekend are things that seem like they could help reduce stress and drug use but infact reinforce the possible drug addiction, as these times allow a time for the user to use drugs such as alcohol.
Society presents drugs as if a normal thing because some drugs are "accepted" and others arn't. Sexually denied worker bees aswell as humans go to alcohol to stave off bad feelings.
Doctors are well respected in the community. So strongly respected that most people think the drugs they give are less harmful than other ones. This notion leads to heavy numbers of drug over doses, addictions, and use.
Tobbacco can contribute to nearly every drug addiction. My post explaining it goes over that in more detail. Link to post
All these factors that contribute to drug use should be edited or controlled. Society needs tweeks if people are to operate like civilized people. The next post will propose an interesting edification.
Johnson MW, Strain EC, & Griffiths RR (2010). Effects of oral caffeine pretreatment on response to intravenous nicotine and cocaine. Experimental and clinical psychopharmacology, 18 (4), 305-15 PMID: 20695686
Unterwald EM, Rubenfeld JM, Imai Y, Wang JB, Uhl GR, & Kreek MJ (1995). Chronic opioid antagonist administration upregulates mu opioid receptor binding without altering mu opioid receptor mRNA levels. Brain research. Molecular brain research, 33 (2), 351-5 PMID: 8750897