WASHINGTON -- A man named Warren walked into a bright blue high-security building about a mile north of the U.S. Capitol on Tuesday afternoon. He emerged with three different kinds of marijuana in hand, determined to figure out which would make him feel better.

"I've never tried it," said Warren with a smile. He wouldn't give his last name.

Just nine people are authorized to purchase medical marijuana in the District of Columbia. Seven are registered to receive two ounces every 30 days from Capital City Care, which opened Monday on a busy corridor of North Capital Street with a clear view of the headquarters of the Bureau of Alcohol, Tobacco, Firearms and Explosives and other Justice Department agencies.

Warren was Capital City Care's third customer. The first two visited the new dispensary on Monday. Another patient, who declined to provide his name but said he has been HIV-positive for 30 years, soon followed. Each provided an identification card before entering a back room accessed only after an employee scans a fingerprint on a biometric lock.

Warren's purchase came 15 years after nearly 70 percent of residents of the nation's capital passed a ballot measure allowing the drug for prescription medical use. Congress repeatedly blocked implementation until 2009, and the city council moved forward with a unanimous vote to allow doctors to prescribe pot for certain chronically ill patients. Now, the city has licensed three dispensaries to sell pot and six cultivation centers to grow the plants.

Marijuana remains illegal under federal law and the Obama administration's approach to medical marijuana has been all over the map , with U.S. prosecutors sometimes going after medical marijuana dispensaries that have complied with state law. Capital City Care executives said they hoped D.C.'s strict regulations, allowing only patients with HIV, AIDS, glaucoma, severe muscle spasms and cancer to receive medical marijuana, will spare them from federal prosecution.

"We haven't heard from them," Scott Morgan, Capital City Care's communications director, said of the Drug Enforcement Administration. "This is really an exhibit in how to do medical marijuana in a focused and sort of clinical kind of way. And for that reason, we hope that the outcomes we're achieving and people we're helping, it sort of stands for itself. When people look at what we've doing here, they'll agree that we're doing the right thing."

Capital City Care currently has more employees than customers, with eight to 10 workers manning the facility and its cultivation center in northeast Washington. In order for the business to succeed, more patients are going to have to sign up.

"We need to see the program grow considerably in order to become sustainable for the businesses involved," Morgan said. "We're not there yet, but we hope to be. Today is a big step towards that. At this point and time, there's been reluctance from doctors so the example that we set at this facility is going to shape the opportunity to bring more patients in in the future."

Warren has been seeing the same doctor since 2008, and he said he took a bit of convincing. "I wouldn't necessarily say ready and willing because he did have his own reservations also like the majority of doctors I'm sure in town right now, but for some reason he felt compelled to help me out," Warren said. "You have doctors that are a bit afraid and patients that are afraid to ask. So it makes it a little hard. Everybody is kind of leery of what could happen, what the possibilities are."

Marijuana policy reformers hailed the new business as a smart step forward for Washington, and encouraged Congress to reevaluate pot laws.

"The District has established a sensibly regulated and tightly controlled system to ensure patients have reliable access to medical marijuana and prevent it from being abused," said Dan Riffle, deputy director of government relations for the Washington-based Marijuana Policy Project. "The establishment of such a model program in Congresss backyard illustrates the need for marijuana policy reform at the federal level. The next step is for Congress to address the banking and tax issues that are preventing medical marijuana businesses from being able to operate as safely and transparently as possible."

Washington and 19 states have now approved marijuana for medical use. New Hampshire joined the list earlier this month, and Nevada was added in June when Republican Gov. Brian Sandoval signed medical marijuana legislation. A bill passed by Illinois lawmakers earlier this year awaits a signature by Gov. Pat Quinn (D).