Nurses warned yesterday that new guidelines allowing them to trick patients into taking drugs hidden in drinks and food could lead to widespread abuse of vulnerable people.

Delegates at the Royal College of Nursing annual congress in Harrogate criticised ethical guidance from the nursing profession's regulatory body, indicating covert medication could be justified "in the best interests of patients".

Nurses said the measure could encourage excessive use of the "chemical cosh" - neuroleptic and anti-psychotic drugs that sedate disturbed patients. Christopher Barber, a disability nurse from the RCN ethics forum, said: "Mind-melting drugs are still routinely administered to meet the needs of staff who see their role as babysitters." Guidance from the regulatory body said this could be justified, "but what can be justified is not necessarily right", he said.

Alan Crump, of the RCN forum for mental health and older people, said: "For too long health professionals have used the term 'in the best interests of patients'... to paper over difficult issues. Now the regulators have done the same."

Barry Aveyard, a nurse in dementia care, warned the guidance was an ethical and legal minefield. The regulators' state- ment was "woolly" and nurses needed specific guidelines.

But Fiona Robertson, a mental health nurse from Guern-sey, said there were good reasons for covertly administering drugs."Most medications taste awful... Patients tend to hoard them and spit them out later, without realising the consequences for their health."

Lisa Crooks, a nurse from West Somerset, said she witnessed the covert feeding of a a "Prozac sandwich" to a confused 82-year-old patient and it saved her life.

The debate was triggered by a statement last year from the UK central council, the nurses' regulatory body. It said it was unlawful to treat a patient without consent, except in an emergency. But when patients lacked capacity to consent or refuse treatment, disguising medication could be justified in their best interests.