A doctor has gone on trial in the Netherlands in a landmark case expected to probe the law on whether patients with advanced dementia can give consent to assisted dying.

Prosecutors argue the unnamed female doctor “acted with the best intentions” but broke Dutch euthanasia law by failing to ensure the consent of a 74-year-old woman with advanced dementia, who may have changed her mind about dying.

It is the first time anyone has gone on trial over a 2002 Dutch law that allows people to ask a doctor to help them die.

The doctor slipped a sedative into the woman’s coffee, before administering a lethal drug, as the patient was held down by her family and struggled against the injection. The woman had previously drawn up an euthanasia statement, but prosecutors say she displayed “mixed signals” about dying.

Euthanasia has been legal in the Netherlands for patients suffering from “unbearable suffering with no prospect of improvement” since 2002. The patient must have a voluntary and sustained wish to die, and at least two doctors must approve the request.

But there are growing questions about whether patients with dementia can be euthanised on the basis of a request lodged before they lost their faculties.

“We don’t think the law is very clear on this point and therefore we don’t think it’s fair to give [the doctor] a penalty,” said Vincent Veenman, a spokesman for the public prosecutor’s office in The Hague. “We never doubted that she [the doctor] had the best intentions in doing this.”

The debate on dementia patients’ ability to consent to assisted dying has intensified since the resignation of a medical ethicist from a regional euthanasia board in 2018. Berna van Baarsen said euthanasia practice in advanced dementia had shifted in a direction she could no longer defend. “It is fundamentally impossible to establish that the patient is suffering unbearably, because he can no longer explain it,” she told the newspaper Trouw.

Euthanasia of people with severe dementia remains rare in the Netherlands. Only two patients with severe dementia were helped to die in 2018, compared with 144 patients with early dementia and 4,000 cancer patients, according to data published on the website of the Dutch national broadcaster NOS.

In 2018, the number of euthanasia cases fell for the first time, a drop attributed to growing fears of clinicians following the decision to investigate this doctor and others.

Prosecutors announced four other criminal investigations into euthanasia in 2018, while the Observer reported in July that the deaths of three women with psychiatric conditions and dementia are also being examined over potential breaches of the 2002 law.

Experts say the trial is an important test case, as people live longer and are therefore more likely to have dementia.

Judges in The Hague are expected to reach a verdict around 9 September.