My grandma has amyotrophic lateral sclerosis and what medicine she should take for relieving the pain? or preventing the further complications?

Medication for ALS: The only FDA approved medication to treat ALS is something called Riluzole (Rilutek). Unfortunately, this medication is neither for pain nor can it cure the disease. Best measures for coping with complications is to understand the progression rate of each person and try to plan ahead such as how to eat, protecting them from choking, helping with breathing, etc. Pain not typically part of ALS.

Comments: Sole drug on market for ALS is riluzole, which can delay tracheotomy but does not enhance strength. Since it inhibits glutamate, maybe pain relief achieved by use of Lyrica (pregabalin) or gabapentin. Most of the approach in ALS is supportive and palliative. Have a family conference with her neurologist.