It is a labour intensive process requiring significant laboratory resource over a number of years, limiting drug companies' willingness to invest.

BBC: Bill gates

With most of the work done by hand without any help from modern technology, its production is a lengthy and labour-intensive process.

BBC: The gateway to Kilimanjaro

Even though the climate is suitable, tea-growing is simply too costly, since the process is labour-intensive and resists automation.

ECONOMIST: America's tea boom