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Weed is a gateway drug — to coronavirus complications.

Experts are warning smokers that even occasional puffs are damaging to the respiratory system, which could worsen symptoms associated with COVID-19.

“Because it attacks the lungs, the coronavirus that causes COVID-19 could be an especially serious threat to those who smoke tobacco or marijuana, or who vape,” says the National Institute on Drug Abuse in a recent announcement.

And that advice could harsh the mellow of more than 43 million Americans age 12 or older who reported smoking cannabis in the past year, according to a 2018 National Survey on Drug Use and Health.

A recent Post report revealed that smoking herb may be on the rise, too, as illegal weed dealers in NYC have seen a spike in sales of 50 percent during the global health crisis.

“What happens to your airways when you smoke cannabis is that it causes some degree of inflammation, very similar to bronchitis, very similar to the type of inflammation that cigarette smoking can cause,” pulmonologist Dr. Albert Rizzo, chief medical officer for the American Lung Association, tells CNN.

“Now you have some airway inflammation and you get an infection on top of it,” Rizzo says. “So, yes, your chance of getting more complications is there.”

The addition of the virus only adds fuel to the flame, he says.

“You’re already making your body fight off foreign particles before it even has to fight off the infection.”

Dr. Mitchell Glass, a pulmonologist and spokesperson for the American Lung Association, adds that cannabis, which often causes a dry cough, can also complicate the diagnostic process.

“COVID-19 is a pulmonary disease,” he tells CNN. “You don’t want to do anything that’s going to confound the ability of health care workers to make a rapid, accurate assessment of what’s going on with you.”

Daily, or “chronic,” cannabis smoking can cause what “looks a lot like chronic bronchitis, which is of course one of the terms we use for chronic obstructive lung disease, or COPD,” Glass says.

Those with COPD or any other respiratory illness, including lung disease or asthma, are at a high risk of developing severe complications due to the coronavirus, which may result in the need for a ventilator to breathe.

And while smoking that green may seem harmless compared to cigarettes, Glass does point out some unique characteristics of weed that differ from tobacco.

“Marijuana burns at a much, much lower temperature than a commercially made cigarette,” says Glass. “Because of that, the person is inhaling a certain amount of unburnt plant material,” which could irritate the lungs in a way similar to common allergens, such as ragweed, birch and oak pollen, he explains.

“So right off the bat there are those patients who would be increasingly susceptible to having a bronchospasm or cough because they have a more sensitive airway.”

Glass also understands the need to reduce anxiety during a viral pandemic — but your doctor won’t advise you to self-medicate with cannabis: “Do you really want to have a confounding variable if you need to see a doctor or a health care worker by saying, ‘Oh, and by the way, I’m not a regular user of cannabis, but I decided to use cannabis to calm myself down’?”