It’s been legal to buy small amounts of marijuana in Colorado for over four years. But consumers can’t order buds, edibles or the marijuana concentrate called “shatter” through the mail — that’s illegal under federal law. And they can’t have weed delivered to their doorstep, like a pizza or an order of pad thai.

Lawmakers in Colorado and other states that pioneered recreational marijuana legalization have been reluctant to allow home delivery, even in an era when consumers are used to getting everything from diamond rings to toilet paper delivered.

Supporters say delivery makes it easier for medical marijuana patients to get their medicine, helps licensed marijuana businesses compete with the black market, and could reduce drugged driving. Opponents say delivery could make it easier for kids to buy drugs and could turn delivery cars into targets for thieves.

Skeptics also say launching a risky service could attract unwanted federal attention. Denver is concerned that marijuana delivery could cause additional safety issues and draw federal scrutiny, according to a statement from Eric Escudero, communications director for the city’s Department of Excises and Licenses. Earlier this year, U.S. Attorney General Jeff Sessions rescinded Obama-era guidance that had told federal prosecutors not to target marijuana businesses that are licensed and regulated.

Colorado legislators last year rejected language in a bill that would have legalized marijuana delivery. Now they’re considering a pilot program instead.

Colorado, Washington state, Alaska and Washington, D.C., don’t allow home delivery of marijuana. Oregon, California and Nevada do, but services are not universal. In Oregon, state data show that close to two-thirds of counties have a dispensary licensed to make recreational marijuana deliveries. In California, marijuana industry advocates say that less than a third of cities and counties in the state allow retail marijuana sales, which could include home delivery.

But illegal and quasi-legal delivery businesses are widespread regardless of the law.

Washington, D.C., for instance, allows cannabis possession but not sales. So businesses, including delivery companies, are selling overpriced stickers, cookies and cold-pressed juice with a gift of cannabis thrown in. “At Juiced, we make sure that all our products make an impact that will enhance your spirit and your mood:),” says one such company’s website, with a coy smiley face emoji.

In Colorado, opponents of legalizing home delivery include law enforcement, county officials, the city of Denver and Gov. John Hickenlooper.

“That notion of having a delivery person go around house to house and dropping off potentially significant amounts of marijuana — any amount of marijuana — I think we look at that as just a hazard,” Hickenlooper told the Cannabist, a website of the Denver Post, last spring when the Legislature was considering legalizing home delivery statewide. “And if we’re really serious about keeping marijuana out of the hands of teenagers,” he said, “delivery service offers more opportunity for that marijuana to get into the hands of kids.”

Home delivery could also bring marijuana sales into counties that don’t allow such sales, said Eric Bergman, policy director at Colorado Counties Inc., a membership association for county officials. More than half of the state’s counties prohibit marijuana businesses within their jurisdiction, according to state data. Some cities within those counties’ borders do allow marijuana businesses to operate.

Marijuana businesses, meanwhile, are lobbying for a change in the law. Advocates for a San Francisco-based marijuana delivery startup called Eaze, which some have called “Uber for weed,” have told Colorado lawmakers that technology can help allay some of their concerns.

For instance, the Eaze app blocks orders to places where delivery isn’t allowed. “Eaze has a whole team of people that monitors, is it legal in that city? Is it legal in that ZIP code?” said Elizabeth Conway, principal at Gide LLC, a firm that lobbies for cannabis and tech companies.

Not all cities oppose permitting marijuana delivery. Former Seattle Mayor Ed Murray argued that allowing delivery would help licensed businesses compete with the black market, potentially driving out illegal businesses. A supplemental budget bill on Washington state Gov. Jay Inslee’s desk would require regulators to study home delivery of medical marijuana.

States that do allow marijuana home delivery don’t allow just anyone to drive around with weed for sale. Oregon’s rules address when pot can be delivered (8 a.m. to 9 p.m.), where (only houses and apartments in the locality where the retailer is licensed), how often (one delivery per person per day), and to whom (adults over 21), for instance. Drivers can’t take more than $3,000 worth of weed products “out for delivery” at one time.

California’s long list of rules includes a requirement that delivery vehicles be outfitted with a GPS tracking system and prohibits “unmanned vehicles” such as autonomous cars from delivering weed.

Cities and counties in both states can opt out of allowing delivery or set more stringent rules, adding further complication. For instance, just 12 of the 88 cities in Los Angeles County are planning to regulate cannabis, said Joe Nicchitta, the countywide coordinator for the Los Angeles County Office of Cannabis Management. Some areas want to allow retail storefronts but not delivery services, some want to allow delivery but not storefronts, and some want both.

In recent years several California marijuana delivery drivers have been robbed, some at gunpoint. Such incidents have been cited by Colorado law enforcement groups in their arguments against allowing delivery services there.

“The concern is that there will be a race to the bottom,” Nicchitta said, where delivery businesses will “locate in the area with the most lax regulations and then deliver all over the county.”