 This is a 10-week, randomised, double blind, placebo-controlled, crossover trial to investigate the effect of Cannabis Based Medicine Extract Sativex on patterns of brain activation associated with movement in 20 MS patients suffering from lower limb spasticity. Spasticity is a common symptom in Multiple Sclerosis MS, occurring all over the course of the disease, particularly in the progressive phase.Physiologically, spasticity and hyperreflexia habitually seen in patients with pyramidal syndrome is due to lesions of other descending pathways, such as the cortico reticulospinal pathways, which participate in voluntary movements.It is now known that an endocannabinoid system acts in humans by at least two types of cannabinoids receptors, CB1 and CB2. There is evidence to support the view that the psychoactive ingredient in cannabis, delta 9-tetrahydrocannabinol delta 9-THC, and cannabinoids in general, can reduce muscle spasticity in people with MS. Aim of the study will be to evaluate the effect of Sativex on: i patterns of brain activation associated with movement fMRI in MS patients suffering from spasticity; ii changes in level of spasticity H-reflex; iii changes in intracortical excitability and on synaptic intracortical network of the motor areas double shock TMS. 