i would say magnesium but might have doubts if it didn't work for you to relieve constipation after megadosing!!! the pharmacist that turned me on to magnesium (after i reported high dose d3 supplementing, and it helped a LOT) also mentioned its needing potassium and that they work together.
sodium and potassium need to be balanced. do you have a high sodium low potassium diet to go with your particular brand of spasticity lew?
(and man, i know what spasticity feels like i use it for a mag-k monitor pretty much!)
my approach: no meds so far - just nutrient-dense anti-inflammatory whole foods, and supplements where needed
info: www.whfoods.com, www.nutritiondata.com