The cannabis industry has come a long way. Four states and the District of Columbia have legalized marijuana, and voters in up to five more states might do the same next year. Plenty of businesses have launched to successfully sell (and legally, I might add) cannabis and extracts.

After activists last week pulled a Denver marijuana initiative from the November ballot, other pro-legalization activists have lashed out at what they see as backpedaling by their like-minded colleagues.

If the initiative had passed (and it looked like it might), it would have allowed limited social marijuana use in businesses such as art galleries and bars.

DENVER (AP) — Colorado is waiving some taxes on recreational marijuana on Sept. 16. A quirk in state law is forcing the one-day tax holiday. Here are some things to know about why Colorado is tapping the brakes on recreational pot taxes:

BLAME (OR THANK) THE CONSTITUTION

Colorado has complicated tax-and-spending restrictions in its state constitution. The restrictions require new taxes to win voter approval and those new taxes to be waived and refunded to voters if overall tax collections exceed state projections.

WHY SEPT. 16

When Chavie Lieber, a writer in New York, was traveling over a recent weekend, she and her husband lent their apartment to a friend’s brother. Upon return, “There were three fat joints rolled for us on the coffee table,” Lieber told me, “with a scribbled note that read: ‘Thanks for letting us stay.’ ”

After moving to a new home in Connecticut, Liza, a marketing executive who spoke on the condition of anonymity, received a small satchel of weed as a housewarming gift from friends, making for “a really mellow” evening in her new home. “I will always appreciate a bottle of wine, but weed is king,” Liza said. “It’s expensive, hard to get, and weed these days is so customized, meaning someone bought Bubba Kush versus Purple Haze, for instance, keeping your tastes in mind.”

State agriculture officials have opened an investigation into a marijuana grow operation named in a report by The Denver Post about pesticide residues, and confirmed a second business named in the story was already under scrutiny.

It is unclear which of the two companies — Mahatma Concentrates or Treatments Unlimited, both in Denver — is already under scrutiny and officials with the Colorado Department of Agriculture would not elaborate.

But the agency said investigations into the businesses’ use of pesticides is the focus of its probe.

The company also has sizable debt but hopes for revenue from three marijuana cultivation projects as it woos the Maine tribe.

The company that hopes to land a contract with the Passamaquoddy Tribe at Indian Township to design and build a marijuana-growing operation on tribal lands is struggling to generate revenue and is carrying substantial debt, according to its latest financial filing.

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Think of it as a back-to-school sales tax break, but for stoners.

Colorado's unusual tax law is forcing the state to suspend taxes on recreational marijuana for one day — Sept. 16 — during which a 10 percent sales tax and 15 percent excise tax won't be collected.

The sales-tax break would shave $20 off the price of a mid-grade ounce of pot in the Denver area, where ounces this summer sell for about $200 before tax.

It's unusual for a state that has many times rejected sales-tax holidays on things like school supplies, clothing or energy-efficient appliances. Officials say it could cost the state $3 million to $4 million.

In the heart of Denver, the newly-minted marijuana capital of America, doctors from around the nation bared unseasonable late-summer frost to attend the Marijuana for Medical Professionals Conference. The event targeted medical professionals with one thing in common—a desire to know more about cannabis medicines as the substance is propelled out of the realms of early 20th-century “reefer madness” and into popular use as a highly-lucrative, 21st-century panacea.

Nearly six months after the city of Denver began a crackdown on unapproved pesticides in marijuana products, a spot-check by The Denver Post found that the chemicals were still being sold to consumers.

Eight lab tests commissioned by The Post on recreational marijuana extracts purchased at two shops found most contained no pesticides that are not approved by the Colorado Department of Agriculture.

But two tests on concentrated marijuana products sold at one store found levels of three pesticides the state says cannot be used to grow marijuana. Both items were manufactured by Mahatma Concentrates in Denver, which made its extracts from raw marijuana grown by Treatments Unlimited, which operates the Altitude shops in Denver.