Hi welcome to healthcare magic forum, In my opinion it will not be a good idea to take dexamethasone and cyproheptadin for weight gain, because both this medications have their own side effects besides doing good it will suppress your immune system and cause drowsiness throughout the day and night, also it will cause adrenal gland suppression leading to various type of abnormality in the body. Best way to gain weight to have balance diet,vitamins, minerals,proper nutrition. Along with that you should go for daily exercise,yoga,meditation,green leafy vegetables,salads,milk,egg,nuts,etc.,Smoking, alcohol and narcotics causes bad health. Hope you understand the situation. Regards, Thanks