Plans to treat more patients in the early stages of Alzheimer's disease with drugs could have a "huge impact" on the Welsh economy, it is claimed.
The Alzeim firm, from Talgarth near Brecon, Powys, farms daffodils for a compound called galantamine, which slows the progress of the disease.
It is doubling the land used to 120 acres (48ha), but said thousands more acres were needed to meet world demand.
The medicine watchdog said drugs could lessen disease symptoms early on.
This reverses earlier rulings that the drugs did not offer sufficient benefit to justify the cost in Wales and England.
The three drugs which look likely to be available to patients with "mild" Alzheimer's are Aricept (donepezil), Reminyl (galantamine) and Exelon (rivastigmine).
In addition, the National Institute for Health and Clinical Excellence (NICE) said a fourth drug, Ebixa, should be prescribed to patients with more advanced Alzheimer's.
Following the decision, Alzeim is planting a further 60 acres (24ha) in the Black Mountains near Talgarth, and will open a production line at new offices in Brecon in a fortnight.
Company spokesman Kevin Stephens said world demand for galantamine was "absolutely huge".
"This could have a huge impact on the Welsh economy and give it a huge boost," he said.
"We anticipated NICE would have to reverse its decision, so we're doubling our acreage to 120 acres and we are building a production line.
"We could have 4,000 acres, but it wouldn't meet the demand for this product."
Mr Stephens said farmers now had the opportunity to diversify and grow daffodils to help meet the demand in a global market for Alzheimer's drugs worth some £8bn.
The firm currently employs eight people, but there are no plans to increase staff at the moment.
Until now, galantamine has been extracted from snowdrops grown in Bulgaria and China.
It is already available in Scotland, but it has to be prescribed privately elsewhere as it is not on NICE's prescription list.
Alzeim's daffodils are grown on the slopes of the Black Mountains after trials showed that the location produced blooms with greater concentrations of galantamine than those grown in lower areas.
In 2008, the company received £850,000 from the Welsh Assembly Government's investment company Finance Wales and private investors to go into commercial production of the drug.
Company chairman Sir Roger Jones said at the time that the business could expand into other areas of Wales if necessary.
There are about 40,000 people in Wales suffering from Alzheimer's and 700,000 in Britain.
Rebecca Wood, chief executive of the Alzheimer's Research Trust, welcomed NICE's plans.
She said: "These drugs hold the promise of relief from the symptoms of Alzheimer's for thousands of people and, while not the cure we desperately need, they can still help."