Cannabis should be available on prescription to stop people who use it to ease pain being criminalised, a group of AMs has said.
Cross-party AMs said many living with conditions such as multiple sclerosis (MS) use illegally-obtained cannabis, putting them at risk of prosecution.
The group has called on Welsh ministers to push for the UK government to act.
But the UK government said it had no plans to legalise cannabis which is a Class B drug.
The Home Office said there is clear scientific and medical evidence that it is harmful.
Rhian Cowen, 46, from Pembroke Dock, has MS and said she could not understand the problem with prescribing medical marijuana.
While she does not use illegally obtained cannabis, she uses products which contain CBD – a non-psychoactive substance found in cannabis – which are not currently licensed for medical use in the UK, but are sold online as supplements.
“While I was going through the process of being diagnosed I stopped taking it, so that the symptoms would re-emerge. I had awful tremors, migraines… all the time,” she said.
“It works right across the board in making you feel better,” she added.
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Four AMs from the Conservatives, Labour and Plaid Cymru – including leader Leanne Wood – have called for a debate in the assembly on Wednesday about medical marijuana.
The debate will trigger a vote in the Senedd, calling on the Welsh Government to ask the UK government to reschedule cannabis for medicinal purposes.
Welsh Conservative AM Mark Isherwood, Labour AM Mike Hedges, and Plaid AMs Ms Wood and Rhun ap Iorwerth said there is “clinical evidence of the effectiveness of cannabis for medicinal purposes”.
Mr Isherwood said: “We have met constituents living with a range of conditions, including multiple sclerosis, epilepsy, dystonia and cancer, who find the benefit of using cannabis for medicinal purposes but by doing so they run the risk of prosecution.”
There is one cannabis-based drug available on the Welsh NHS for MS sufferers – called Sativex – but the MS Society has said that access to the drug has been patchy. It is also not available outside Wales.
Mr Hedges, Labour AM for Swansea East, said: “We shouldn’t interfere with doctors’ ability to prescribe”.
Ms Wood added: “The clinical and anecdotal evidence of the effectiveness of cannabis for medicinal use is compelling.”
The matter is not devolved, with the Medicines and Healthcare Products Regulatory Agency responsible for medicines regulation.
A Home Office spokeswoman said: “We recognise that people with chronic pain and debilitating illnesses are looking to alleviate their symptoms.
“However, it is important that medicines are thoroughly tested to ensure they meet rigorous standards before being placed on the market, so that doctors and patients are assured of their efficacy, quality and safety.
“Cannabis is a controlled class B drug, as there is clear scientific and medical evidence that it is a harmful drug, which can damage people’s mental and physical health, as well as harming individuals and communities.”
Newport West MP Paul Flynn has proposed a bill legalising cannabis for medicinal purposes in Parliament.
A Welsh Government spokeswoman said: “Cannabis derivatives can play a role in treating some medical conditions and we made Sativex available in Wales because it went through a highly-regulated quality assurance process.
“But using an illegal raw drug of unknown quality is not how we want to provide medicines.”