If I know correctly the Sativex you mentioned is not a treatment drug for MS. It can be prescribed to treat spasticity caused by multiple sclerosis. I know that it's available in several countries in Europe, but I'm not even sure if it's approved in the US. However Tysabri it is a treatment drug for MS, but you should be aware of the PML complication associated with it. There are several drug related progressive multifocal leukoencephalopathy lawsuits going on because of that.
In any case you should consult your doctor for advice, especially with such a serious disease like MS.