The Royal College of Nursing (RCN) has voted to decriminalise cannabis for medical use.
It will lobby governments across the UK after a resolution at its annual general meeting of members in Belfast was passed to help those suffering terrible pain to legally obtain relief.
The UK Government's position is that, as a Class B drug, cannabis is subject to strict restrictions and cannot be prescribed, administered or supplied to the public. There are claims tens of thousands of people in pain are breaking that law.
RCN chief executive Janet Davies said: "The evidence is quite compelling on what people are doing themselves."
She added: "These are people who want to try something because they are suffering.
"That terrible pain that people can be in - people feel that something that will relieve that pain is worth a try."
Some MPs have said there is clear evidence cannabis could have a therapeutic role for some conditions, including chronic pain and anxiety.
They have claimed tens of thousands of people in the UK already break the law to use the drug for symptom relief.
The NHS has said cannabis use risks impairing driving ability and causing harm to lungs if smoked as well as ill effects on mental health, fertility or unborn babies.
Under laws in England and Wales, cannabis is not recognised as having any therapeutic value and anyone using the drug, even for medical reasons, could be charged for possession.
RCN member Catherine Gault from Northern Ireland told the RCN Congress: "There is strong enough evidence to support the use of cannabis to treat pain.
"It would not be a recreational drug for me, it would add quality to my life."
She has an underlying medical condition and said she risked developing pain which could no longer be treated by the NHS.
The resolution was proposed by the Suffolk branch and endorsed by members of the general meeting.
Over 40 countries, including Italy, Finland, Australia, Canada, Switzerland, Germany and half of the United States have decriminalised cannabis in some form.
Tincture (a solution) of cannabis was medicinally available in the UK until implementation of the Misuse of Drugs Act by the UK Government in 1973.
Attempts have since been made to change existing policy in the UK, including a recent petition presented to the Prime Minister, but none have been successful.
According to the RCN, the Conservative and Labour parties officially oppose the legalisation of cannabis for any purpose, while the SNP, Plaid Cymru, the Green Party and the Liberal Democrats support a change in law.
In 2017, the MS Society took the position that there is enough evidence to support medicinal use of cannabis to treat pain, when other treatments have not worked.
A range of polls demonstrate that there is support for change.
The proposers of Tuesday's resolution said: "The RCN must join these voices and support the complete decriminalisation of cannabis for medicinal use."
Peter Carroll, campaign director of End Our Pain that counts 75 MPs amongst its supporters and is calling for a change in the law to allow access to medical cannabis under prescription from a medical professional, said: "This move from the RCN will add to what feels like an unstoppable momentum for change amongst medical professionals and politicians."
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