A decision by the UK government to ban the stimulant khat later this year is facing fierce resistance in Kenya from those farming the mildly narcotic leaves for export, reports the BBC's Gabriel Gatehouse.
As the sun rises over Meru, in Kenya's central highlands, the khat pickers get to work.
A dozen men, some quite elderly, climb nimbly into the willowy trees; it is a precarious business.
They are after the youngest, freshest shoots, so they have to get right to the top; and they have to be quick.
"It all happens in the morning; it has to be taken to the market when it is extremely fresh," says Jeff Kubai.
In his day job, Mr Kubai is a professor of psychology.
But like many here, he also farms khat, or miraa as it is known locally.
His family has cultivated the stimulant for generations.
"It's a stimulant which gives the mild impression of happiness," he says, as he chews on one of the deep purple shoots.
I try some myself.
Following Mr Kubai's lead, I pull off any leaves, then bite into the soft top of the shoot.
'All good things are bitter'
As I chew, I strip the remaining bark off the sprig with my teeth; then more chewing - but you're not supposed to swallow.
"It tastes bitter," I complain.
"All good things are bitter - including beer," says Mr Kubai.
Personally, I find beer has a stronger and more immediate effect on my happiness levels.
But in this region, chewing khat has a long and venerable tradition.
"Warriors used to chew it," Mr Kubai tells me, "to keep the enemies at bay. And also to take care of the cows in the jungle.
"The elders used to chew it as they deliberated on community issues.
"When they were in their traditional parliament, one ingredient which kept them going was the miraa."
I think you have to chew a lot more than I managed, because I must admit I did not feel any discernible effect other than a rather unpleasant taste in the mouth.
But the habit has spread, and in Meru they estimate that 80% of the local population now rely on the khat industry in some way for their living.
"This shamba (farm) brings a turnover of about 200,000 Kenyan shillings per month (about $2,300, £1,500)," Mr Kubai says.
"This is money that is used to build churches, take children to school, build infrastructure, do everything.
"Basically, the livelihood of the people here depends on these trees."
Not surprisingly perhaps, local leaders are not happy with the UK's decision to reclassify khat as a class C drug.
At a meeting of khat growers and merchants, I meet Omar Ahmed.
He is an exporter from Kenya's Somali community, where khat is especially popular.
Exports to the UK account for around 15% of the total production in Meru, worth an estimated $7.5m (£4.9m) annually.
Mr Ahmed is facing substantial losses.
"We will do whatever we can to show the British government that if you don't take care of our interests, you shouldn't expect us to take care of your interests also," he says, while nibbling away at a bunch of khat.
Everyone at the meeting appears to have been chewing khat for quite a number of hours; tempers are running high.
I think Mr Ahmed might be a little high himself.
But there is more to this than just the idle threats of a disgruntled businessman.
The local MP, Kubai Kiringo, tells me Kenya could reconsider its ties to Britain if the UK does not drop the ban.
"We feel bitter and short-changed. We want the home secretary to revise her decision," he says.
"If she doesn't, then we shall look for other avenues to show that we are not happy."
The UK maintains a large military base in central Kenya, where thousands of British soldiers train every year before deploying to Afghanistan and other conflicts.
"Meru County residents won't be happy to see the people who banned their miraa coming to train in their area," Mr Kiringo warns.
"British tourists come for recreation and we have British farmers here," he continues.
"Meru people will not be happy to see them reap from our soil when they have already banned our commodity.
"So we beg them to reconsider their decision because it will have ripple effects at the end of the day."
Once the khat is bundled up, it is packed into white sacks, loaded high on to pick-up trucks which then speed their way down the winding mountain road to the capital, Nairobi, for export.
When the ban comes into effect later this year, the UK's policy will be in line with that of the US, Canada and most of the European Union - all of which have classified khat as a drug.
Campaigners say addiction to the stimulant is pulling families apart.
But that is not how they see things in central Kenya, where khat is both a living and a way of life.