I joke with my children and friends that I'm the poster pensioner for pot now I've joined this campaign.
The 64-year-old said the devastating effects of multiple sclerosis have left her dependent on the illegal drug for the pain relief she feels it gives her.
Mrs Cox, from Cwmbran, Torfaen, served with Gwent Police in the late 1970s before leaving to start a family.
She has now joined a group – which includes the Multiple Sclerosis Society and the Dystonia Society – calling for cannabis to be made available for medicinal purposes in Wales.
The group met with AMs on Wednesday to discuss the drug’s use for pain relief.
Mrs Cox is all too aware of the consequences of the illegal drug, given her former profession.
She said she wants cannabis legalised for medicinal use in Wales so that she can use it without breaking the law.
“When I was diagnosed with MS in 2014, the doctors prescribed me with a cocktail of medicated drugs that left me so weak that on a good day I could just about manage to sit up on the edge of my bed for 20 minutes,” she said.
“I was like a zombie and as weak as a kitten. I felt nauseous most of the time and I was concerned about the level of chemicals, especially liquid morphine, going into my body.
“Then a year ago, I read something on the internet about cannabis and how some MS sufferers believed it gave them pain relief. I thought ‘I need to try this’, but had no idea where to get hold of it.
“It was ironic, really, because during my days as a serving police officer, I’d been on drugs raids and actually seized cannabis.
“I joined the police because I believed in the rule of law. Even if I hadn’t been an officer, I would still not like breaking the law but, having said that, if there is something out there that is going to relieve the pain in my muscles, I am jolly well going to use it.
“Getting hold of the cannabis was my biggest problem initially. I do not want to go into detail about how I have overcome that problem, other than to say that the cannabis is not bought. It is given to me by someone.
“The positive effects of smoking it were immediate. My brain and my muscles felt completely relaxed and, for the first time in ages, I felt nice and calm.
“I still take codeine (painkiller) to take the edge off my pain but it is only the cannabis that can eliminate it.”
The NHS warns that cannabis can harm people’s mental health, fertility and lungs.
Her use of the drug is something Mrs Cox has had to explain carefully to her 13-year-old grandson.
“I have to be sensitive to that,” she said.
“He told me he was worried about me because he’s been told drugs are dangerous. It was a difficult conversation.
“I told him I don’t want him to go out and do it because he isn’t ill.
“I joke with my children and friends that I’m the poster pensioner for pot now I’ve joined this campaign.
“But there is a serious side to this. As things stand, people are having to put themselves at risk. They shouldn’t have to be diving into dark corners to buy something that might be cannabis or it might be a packet of dried sage.”
Cannabis is used for medicinal purposes in Germany and Switzerland – people are allowed to import it for medical use.
Canada, the Netherlands, Israel and 20 US states regulate herbal cannabis for medical use,
The Welsh NHS was the first in the UK to fund a cannabis-based drug for MS patients.
But the Welsh Government does not have the power to legislate on drugs and a spokesman said: “Legal classification of drugs is not a devolved matter and remains a responsibility at a UK government level.
“We consider this to be appropriate as the legal classification of drugs should be considered on a UK-wide basis.”
The Home Office has been asked to comment.
By BBC Wales