Has anyone heard of Sativex for cancer pain?

My mom has Merkel Cell Carcinoma which is moving really fast in her body. She has decided NOT to chase it down anymore and just let it take it's toll. But she is in constant pain, and the nausea that she has causes her to throw up every single day. She is literally wasting away at this point. She has tried morphine but it also makes her sick. The problem is she is very sensitive to ANY pain meds and has tried pretty much all of them through her doctor. I know there's a marijuana pill called Marinol which is only THC from the actual plant. But I've heard of a liquid that you spray under your tongue called Sativex which is supposed to be much more effective. The UK legalized it years ago, and I think Spain has but as usual the US is slow because of the whole marijuana thing here. I'm wondering if anyone has heard of it, tried it, and what they have to say about it. I will pursue this option for her since it's supposed to help with nausea and pain, but only if it's worth pursuing.