NEW YORK (CNNMoney) -- Marijuana entrepreneurs are capitalizing on 4/20, the annual pothead holiday, as an opportunity to sell even more weed than usual.
"This is our industry's Oktoberfest and New Year's Eve all combined into one," said Dr. Stuart Titus, CEO of Medical Marijuana, Inc., a California-based online purveyor of hemp oil who's offering a 4/20 discount of 35%.
Why did April 20 became the annual celebration for cannabis? The explanations are murky and filled with urban legends, though it hardly seems to matter at this point. What's important is that lots of people openly smoke pot in an extra-celebratory way on April 20.
RELATED: 4/20: The hazy story of how it became marijuana's high holiday
"We're just expecting to get slammed," said Craig "C.J." Fuchs of Studio420, a pipe shop and smoking room in Englewood, Colorado. "We're expecting to be probably packed from Thursday to Sunday."
Fuchs, who owns the business with his father, Marty, said he's doubling his usual entry fee to $20 for the 4/20 weekend. Patrons are allowed to smoke at Studio420 even though Fuchs doesn't sell weed, just the merchandise for it. But for those retailers who do, 4/20 provides an annual boom for pot sales.
"What we do see is a pretty heavy spike, anywhere from 30% to 40% in the week leading up, and in the days after," said Grant Pettrie, sales director for Denver-based Potguide.com, an information source on marijuana law and business as well as dispensaries and discounts. "There's more of an uptick because it's becoming more accepted."
Recreational marijuana is legal in Washington, D.C., and eight states, including five states that legalized it just last year. In Colorado, Oregon and Washington state, all of which have had a legal recreational market for years, 4/20 has taken on the trappings of a de facto sales holiday, like Valentine's Day for florists and jewelers or New Year's for health clubs and liquor stores.
"Yes, 4/20 really does show a large increase in sales," said Justin Viviani, manager of The Oregon Weedery, a dispensary in Portland. "Last year 4/20 was on Wednesday, traditionally our slowest day of the week, and we saw a 300% increase in visits and sales."
Viviani said he'll be offering discounts on new products, as well as live music at the dispensary with free "non-medicated" snacks.
This year, 4/20 is on a Thursday, which puts it closer to the weekend. Viviani believes this could lead to even stronger sales, so he's stocking up.
"We will be heavily staffed with extra budtenders that day," he said. "We package our own flower and craft our own joints so we will be doing a lot of pre-work just to stay stocked."
It's not just dispensaries that see extra business around 4/20. Retailers that sell smoking implements, marijuana-themed clubs and smoking rooms and producers of cannabis products like edibles and tinctures also get boosts.
According to New Frontier, a research company that analyzes the marijuana industry, sales on 4/20 tend to be several times higher than on other days, and discounts play a role in driving that.
In classic Black Friday fashion, many retailers offer 4/20 discounts of up to 30% for medical marijuana, and up to 50% for recreational, according to Pettrie of Potguide.com.
"This is a really good time to stock up on product," he said.
Green Man Cannabis, a company with two dispensaries in Denver, fuels the 30% sales bump it has seen on 4/20 with discounts of nearly 50% on pre-rolled joints and 20% on marijuana purchases of at least a quarter-ounce.
Native Roots, a company with 14 dispensaries in Colorado, is marking 4/20 with its "smokin' token promotion," where any customer buying an ounce of marijuana during the month of April could potentially win 12 free ounces, distributed one per month over the next year.
But not everyone is jumping on the 4/20 band wagon. Punit Seth, CEO and co-founder of the newly released marijuana brand Toast, isn't offering any discounts for his $85 10-packs of cannabis cigarettes.
"4/20 is almost like St. Patrick's Day for alcohol; it's about getting as messed up as possible," said Seth, whose web site depicts models in suits and furs puffing weed in a chic-looking lounge. "We want our product to be held in a different light."