Maria Rivera showed up at a Near West Side dispensary Tuesday afternoon to stock up on some of her favorite pot products a day before the drug is fully legalized statewide.

Rivera suffers from rheumatoid arthritis and regularly buys cannabis flower and pre-rolled joints at The Herbal Care Center, 1301 S. Western Ave. But Tuesday, she left empty-handed after realizing that her go-to choices weren’t in stock.

“On and off it’s been like that,” she said. “They don’t have as big a variety as when I first started coming in September, so I don’t know what to do.”

While officials and industry analysts have long warned of an imminent supply shortage, dispensaries licensed to sell both medical and recreational pot are required by law to keep a reserve of product for medical patients when the new sales kick off.

Like many of the state’s pot shops, The Herbal Care Center is pulling out all the stops for its first recreational sales. The shop — operated by Perry Mandera, the former owner of VIP’s A Gentleman’s Club — is setting up heated tents and offering free cocoa and coffee to the expected throng of new customers who will likely have to wait to purchase legal recreational pot. Waiting patrons will ultimately receive a text when they can move inside.

Michael Mandera, Perry Mandera’s son and the store’s general manager, said his staff will be ready for the influx of new customers. The Herbal Care Center is the biggest pot shop in the state, according to Michael Mandera, who claimed it also offers “the largest inventory.”

But the huge LED screens that line the walls of the dispensary’s showroom floor painted a different picture. The dispensary was offering only a single varietal of both indica and sativa flower — although there were eight hybrid options on the menu. And while the dispensary had ample options for patients looking for vaping products, edibles and topicals, there were limited pre-rolls for sale.

During a walk-through of the store, Michael Mandera remained confident that the shop will “be able to adequately supply everybody.” He noted that additional weed strains will be available when recreational sales start.

Mark de Souza, CEO of Goose Island-based Revolution Global, said operators of Illinois dispensaries “just can’t get enough product” and are frequently inquiring about purchasing more from the company’s cultivation facility in Delavan.

“It’s gonna take some time for that supply chain to get better and get mature,” said de Souza, who is concerned that officials aren’t properly regulating the stockpiling of pot.

“Everybody we know continues to do their best to supply consumers and I certainly hope that there has not been excessive stockpiling,” he added.

Michael Mandera acknowledged that his shop has been stocking up on weed for months. The Herbal Care Center has added a handful of new employees — 24 who will be working New Year’s Day. In recent months, the dispensary has also added additional point-of-sale systems to handle recreational buyers.

Despite taking measures to accommodate new customers, Michael Mandera claimed the store’s medical patients will be given priority. In addition to having access to the dispensary’s reserve stash, Michael Mandera said, they also won’t have to wait in line to get inside.

But a second medical patient, who asked not to be named, complained Tuesday about waiting to get inside to peruse the store’s spotty supply.

“I came here and I sat and waited. You can’t get no pre-rolls, you can’t get any flower,” said the woman, a cancer patient who suffers from peripheral neuropathy she developed during chemotherapy.

Frustrated with the treatment, the woman is considering taking her business elsewhere. Given that medical patients can only purchase pot at one chosen dispensary, she would have to buy recreational pot that’s subject to hefty taxes.

“I’m coming in here because I have to come in here,” she said. “That’s not fair to have medical patients wait this long and you don’t have anything that they need. And you know you don’t have it.”