The wall of prohibition began to show cracks when it became accepted that marijuana has medicinal uses.
Medical marijuana dispensaries have clients who suffer ills ranging from cancer to AIDS to chronic pain. Proponents say the drug's pain-relieving properties offer an alternative for cancer patients undergoing chemotherapy or radiation treatments.
Opponents, however, say that science has yet to prove that marijuana is safe.
A series of trials published by the University of California Center for Medicinal Cannabis Research last year showed cannabis can help patients suffering from neuropathic pain, commonly caused by degenerative diseases like multiple sclerosis or fibromyalgia. Neuropathic pain is also a common side effect of chemotherapy and radiation.
Study participants on cannabis reported a 34% to 40% decrease in pain, compared with the 17% to 20% decrease seen in patients on a placebo drug.
The National Institute on Drug Abuse, meanwhile, says that marijuana causes an increase in heart rate, which could put users at risk for a heart attack or stroke. Marijuana smoke also contains carcinogens similar to those in tobacco smoke.
Jason David, whose son Jayden suffers from seizures, turned to the drug and calls it "miracle marijuana."
Jayden has Dravet syndrome, a rare and catastrophic form of childhood epilepsy. The boy started taking a liquid, nonpsychoactive form of marijuana, which his father says controls his violent seizures. This form ensures that Jayden does not get high from the drug, his father says, but has allowed him to enjoy the things other boys do.
Medical marijuana dispensaries are not what you imagine
Spurlock said he imagined that marijuana dispensaries -- the places where patients can purchase medical pot -- would be shady places. What he found at Harborside Health Center, the largest dispensary in the country, surprised him.
The space was large and clean, nicer than many health clinics he has been to, Spurlock said. Tight security regulated who could enter the business, which sells various strains of marijuana and lotions, pills and other products derived from the drug.
Some strains of marijuana are known to be more cerebral and energizing, while others are more sedative in nature and have greater pain-relieving properties. Dispensaries such as Harborside categorize their products accordingly and have specific strains for different ailments.
Marijuana laws put state and federal statutes at odds
Eighteen states have either decriminalized or allowed medical marijuana in some fashion. While the state laws have allowed dispensaries to open, they remain illegal under federal law. The gap between state and federal laws is widening when it comes to marijuana enforcement.
For instance, state law makes it legal to possess marijuana in Washington state, but selling drugs is still a federal crime. There is a similar situation in California, where medical marijuana is allowed, but again, growers don't have the same legal protections that users have.
Pot smokers in Washington celebrated in Seattle's Space Needle by toking up as the law legalizing weed went into effect, but growing and selling it remain felonies.
"So I'm not sure where you're supposed to get it," King County Prosecutor Dan Satterberg said when the law went into effect. "If you stumble across some on the street or it falls from the sky, then you can have it. Otherwise, you are part of a criminal chain of distribution."
In 1996, California voters approved Proposition 215 to exempt doctors and seriously ill patients from marijuana laws and allow them to grow and use it in treatment. But government crackdowns on growers since then have led to multiple lawsuits.
Harborside, the dispensary that Spurlock visited, is fighting to remain open amid efforts by the feds to shut it down.