Scientists have figured out how to brew morphine using the same kit used to make beer at home.

They have genetically modified yeast to perform the complicated chemistry needed to convert sugar to morphine.

The findings, published in Nature Chemical Biology, raise promise for medicine but also concerns about "home-brewed" illegal drugs.

Experts have called for tight control of organisms genetically modified to produce narcotics.

Brewing bad

If you brew beer at home, then you are relying on microscopic yeast that turns sugars into alcohol.

But by borrowing DNA from plants, scientists have been genetically engineering yeasts that can perform each of the steps needed to convert sugar into morphine.

One stage of the process - the production of an intermediary chemical called reticuline - had been a stumbling block.

That has been solved by a team at the University of California, Berkeley, and the scientists say it should now be possible to put all the steps together and "brew" morphine.