Prosecutors in England and Wales received fresh guidelines on assisted suicide to make it easier for them to decide whether to charge people who have helped sick loved ones to die.
However, mercy killers would still face the full force of the law, said Keir Starmer, the Director of Public Prosecutions.
The new guidelines follow a legal ruling and calls for clarification after dozens of cases where people helped partners and relatives to die abroad.
"The policy is now more focused on the motivation of the suspect rather than the characteristics of the victim," such as whether the suspect was wholly motivated by compassion, Starmer said.
"The policy does not change the law on assisted suicide. It does not open the door for euthanasia.
"What it does is to provide a clear framework for prosecutors to decide which cases should proceed to court and which should not."
Assisted suicide and mercy killing has been at the centre of fierce debate here after a string of recent high-profile cases.
Last week, veteran BBC broadcaster Ray Gosling was arrested and bailed on suspicion of murder after admitting on television that he had smothered to death an ex-lover who was seriously ill with AIDS.
There were also two recent cases of mothers who killed their seriously ill children, one of whom was jailed.
Starmer wrote in Thursday's Times that "assisted suicide involves assisting the victim to take his or her own life" while "someone who takes the life of another undertakes a very different act".
Helping someone to commit assisted suicide is still illegal in England and Wales and carries a maximum sentence of 14 years' imprisonment.
However, more than 100 people with incurable or terminal illnesses have gone to the Dignitas clinic in Switzerland to die and none of those involved in helping them to do so have been prosecuted.
Under the guidelines, factors weighing against prosecution include that the victim had reached a clear and settled decision to die and that the suspect had tried to dissuade them.
Factors in favour of prosecution include the victim being aged under 18 and the suspect having a history of violence or abuse against them.
Starmer was forced to issue the guidelines after a legal ruling in the case of multiple sclerosis sufferer Debbie Purdy, who wanted to know whether her husband Omar would be prosecuted for helping her end her life.
The guidelines "really clarify the difference between malicious encouragement and compassionate support for somebody's decision," Purdy said.
"Omar and I can now get on with our lives.
"Because I will know the likely consequences of any decisions I choose to make about my death, I won't have to make those decisions early."
Sarah Wootton, chief executive of Dignity in Dying, called the guidelines "a victory for common sense and compassion".
Author and assisted suicide campaigner Terry Pratchett, who suffers from Alzheimer's disease, welcomed the guidelines and called for the medical profession to be allowed to help people end their lives.
"I hate the thought of amateurs helping amateurs to commit suicide," he said.
However disability charity Scope warned: "There is a real danger these changes will result in disabled people being pressured to end their lives."
In parliament, lawmakers called for a debate on assisted suicide, with some concerned the guidelines could open a "new back door" to euthanasia.
British Prime Minister Gordon Brown has warned against legalising assisted suicide, saying it risked putting vulnerable people under pressure to terminate their lives.
Scotland does not have a specific law on assisted suicide, while Northern Ireland has been conducting its own consultation.