New guidance has been issued to clarify the law on assisted suicide in England and Wales - but it offers no guarantees against prosecution.
Instead the director of public prosecutions has spelled out the range of factors that will be taken into account when deciding on cases.
These include whether there was a financial motive, and looking into how the decision to die was made.
The guidance does not represent a change in the law.
Assisting suicide is illegal and carries a jail term of up to 14 years.
However, more than 100 Britons with terminal or incurable illnesses have gone to the Swiss centre Dignitas to die and none of the relatives and friends involved in the cases has been prosecuted.
This is because the authorities have the power to use their discretion under the terms of the act.
Keir Starmer QC, the director of public prosecutions, was forced to publish the guidance after a long-running legal fight by Debbie Purdy, a multiple sclerosis sufferer from Bradford.
In July, Law Lords ruled she had the right to know under what circumstances her husband would be prosecuted if he helped her travel abroad to die.
Mr Starmer said he hoped his guidance would now bring greater clarity to the issue, although he added all cases would still be investigated by the police.
He said: "There are no guarantees against prosecution.
"It is my job to ensure that the most vulnerable people are protected while at the same time giving enough information to those people, like Ms Purdy, who want to be able to make informed decisions about what actions they choose to take."
Among the factors which would determine a prosecution are:
The new framework will come into force immediately - although a consultation is also being launched with the final policy not expected to be published until the spring.
Ms Purdy welcomed the intervention by the DPP.
She said it was important to underline that people considering suicide had a duty first to carefully consider all possible options.
"People will know what they must make sure of before they assist, and hopefully that will give people confidence not to make such a decision until the last possible minute."
And Sarah Wootton, chief executive of the Dignity in Dying campaign group, agreed, saying the guidance represented a "significant breakthrough".
But Dr Peter Saunders, of Care Not Killing, an umbrella group of doctors, religious organisations and charities, said there were some features that were "disturbing".
He claimed having details spelt out like this could make prosecutions less likely.
"There must be a real danger that this will be seen as giving the green light to assistance from close relatives or friends, who in many cases might be those who would stand personally to gain from the death of the deceased."
The law is similar in Northern Ireland and new guidance being issued sets out an almost identical framework.
In Scotland there is some uncertainty as there is no specific law on assisted suicide, although in theory someone could be prosecuted under homicide law.
A bill is expected to come before the Scottish parliament soon in a bid to legalise assisted suicide.