Media playback is unsupported on your device Media caption Will voters legalise or 'just say no'

We are travelling through Denver inside a tour bus with a twist.

A disparate group of some two dozen people are relaxing - that is definitely the word - on plush benches which run along the sides of the vehicle.

They are not here to gaze at the Rocky Mountains. These tourists have come to the Mile High City to get stoned.

"Ready to get high," ask Stacey and Mia Jane, our cheerful, charming guides. The instant cheers and wide grins from the entire bus tell you that this is a rhetorical question.

The driver is sealed into his compartment, in the back a music video blasts out and the passenger compartment is soon filled with a thick fug of smoke.

Welcome to Colorado where recreational marijuana use has been legal since January 2014 and where an entirely new business - cannabis tourism - has taken off.

For many of the passengers this is a remarkable change after spending years hiding their habit in the shadows.

Marijuana has been smoked or otherwise ingested by humans for at least 2,000 years but for much of the past century it has been demonised.

The 1936 propaganda film Reefer Madness set the tone, suggesting that the drug led to murder, suicide and other horrors.

Image caption Some states are bringing in millions of dollars in taxation from the industry

Billions of dollars has been spent on tackling suppliers and enforcing abstinence. And yet now, puff-by-puff, state-by-state, Americans are rehabilitating the herb.

Today it is a legal medicine in 25 US states. Four - Alaska, Colorado, Oregon and Washington - allow recreational use, as does the District of Columbia.

On November 8, as well as choosing a president and sending politicians to Congress, voters in Arizona, California, Maine, Massachusetts and Nevada will decide if they want to join the recreational users.

Propositions to allow medical marijuana are on the ballot in Arkansas, Florida, Montana and North Dakota.

'Still a lot of stigma'

In Denver, the state government is raking in millions of dollars in taxation from the fledgling industry, according to Mike Eymer, who runs Colorado Cannabis Tours. But, he argues, the business isn't yet treated equally.

"We still deal with a lot of stigma. We have to jump through a lot of hoops with the regulators. They treat this stuff as if it's nuclear castings," he complains.

Among the federal regulations are restrictions on the ability of cannabis-related businesses to use bank accounts.

In March, an official statistical analysis for the Colorado Department of Public Safety concluded that it was "too early to draw any conclusions about the potential effects" of legalising the drug "on public safety, public health, or youth outcomes".

Image caption Polls in California suggest voters will back the use of recreational marijuana

But the chief prosecutor in Denver insists there has been a rise in violent crime as cash and drugs at marijuana facilities are targeted by armed robbers.

And that's not the only aspect of the industry which concerns District Attorney Mitch Morrissey.

He is worried about traffic accidents as well as the effects on health and education and he has a message for voters elsewhere: Don't end up a "Stoner State" like us.

"Why don't you wait? Because you have a guinea pig out there and it's called the state of Colorado.

"You're making a public policy decision that could have an impact on an entire generation of Americans."

Mr Morrissey says "greed" is the driving factor behind the relaxation of drugs laws.

'Mecca of marijuana'

Visit Desert Hot Springs and you can see his point. Except that here, in this unremarkable and unloved settlement in California's Coachella Valley, they would rather call it a business opportunity.

In recent months patches of barren, dusty land have been changing hands for hundreds of thousands of dollars. Why? Because the town council has decided to embrace and encourage the growth and sales of marijuana.

At present the Wikipedia entry for Desert Hot Springs - upstaged for years by its fashionable tourist resort neighbour Palm Springs - does not even mention the trade.

Jason Elsasser of CV Pharms, a budding cultivation company, thinks that will soon change.

"It's going to be the Mecca of marijuana," he says.

"If what they have just approved so far was built - if they quit taking applications - their budget of $15m a year would increase to $35m to $40m a year," he says, referring to local taxation on production of medical marijuana.

If recreational use is approved on election day, Mr Elsasser reckons that his "humble little town" will go boom.

Image caption Tour operator Mike Eymer speaks to cannabis tourists in Colorado

Back in Colorado, tour operator Mike Eymer is also eyeing California with interest.

He has plans to expand into the Golden State if it votes yes on Proposition 64.

"We raise more money than alcohol taxes do and we don't cause nearly the problem that alcohol does," he says.

But even if Californians approve the measure, as polls suggest they will, marijuana will still not be out of the shadows entirely.

Federal law continues to brand the drug as dangerous and prohibited.

It is a glaring and thorny contradiction, typical of the tussles between state and federal power and between authoritarians and libertarians in the United States.

The Drug Enforcement Administration has twice refused to downgrade cannabis from a Schedule I substance alongside heroin, LSD and MDMA (ecstasy) to a less dangerous Schedule II substance, arguing that it has concerns about patient safety and a "high potential for abuse."

That position may not be sustainable for much longer if millions more Americans use the ballot box on election day to say no to the war on drugs.