His weight gain is most probably due to Depakote which is known for causing weight gain. Weight gain is mostly due to deposition of fat in abdominal area. There are many other causes of weight gain such as increased food consumption without increasing physical activity and high junk food intake.
Syntrax protein powder does not help in losing weight. Rather it is deleterious for kidney as it might cause damage to basement membrane of kidney which is a membrane which helps in filtration. Weight loss can be possible by proper diet management and workout in gym. Adopt natural ways of losing weight.
Advice
1.     Continue Depakote as suggested
2.     Avoid Syntrax protein powder
3.     Ask him to start workout in gym at least for half an hour for 4 – 5 days in a week regularly. Start with a balanced mix of cardio, weight training and flexibility exercises
4.     Avoid eating high energy foods such as cakes, chocolates, chips etc.
5.     Avoid alcohol and smoking
6.     Increase consumption of high fiber diet such as wheat bread, dry date and vegetables etc.
7.     Drink 3 – 4 liters of water daily
8.     Chew the food properly to make it easily digestible
9.     Avoid excess intake tea and coffee after meal
10.     Divide your meals into smaller portions and eat them frequently during the day
11.     Avoid oily & spicy food
I hope this information will help you. I will be happy if you ask another question
Thank