Image copyright Getty Images Image caption Ms Miller said she made the ricin from the castor beans she grew from plants in her apartment

A woman living in a US nursing home has admitted making ricin and testing it on other elderly residents.

Betty Miller has been charged after ricin was found in a care home in Shelburne, Vermont.

Investigators said Ms Miller made the highly toxic powder from castor plant seeds.

Ms Miller told authorities she made between two and three tablespoons of ricin in her kitchen.

The alleged poisonings were uncovered earlier this week when Ms Miller drove herself to a local medical centre to be evaluated.

The ricin was found on Tuesday afternoon in her apartment.

Ms Miller said she grew 30 to 40 castor beans from plants.

In court documents, she said "her goal was to injure herself".

However, she sought to test the effectiveness of the plant-based poison on others in her care home.

Ms Miller told FBI investigators that she put ricin in the food and drink of other residents on at least three occasions.

No other residents have reported any symptoms that could be consistent with ricin poisoning, however.

According to the FBI, Ms Miller was not licensed to possess ricin.

She has been charged with knowing possession of an unregistered select agent.

According to local media, the Wake Robin nursing home declined to comment. It said that it would not release details about its residents.