Which medicine should I use to gain weight

medication to gain weight :
- there is some simple medication that can increase your appetite thus increasing your weight such as :
1. Dronabinol 
2. Megestrol 
3. Oxandrolone
- first consult internal medicine doctor before taking any of those medications 
Vitamins that help with increase weight ?
1. vitamin C 
2. vitamin B1 / B6
3. vitamin A
Causes of weight loss :
1. unhealthy diet 
2. smoking
3. stress
4. medication side effects 
5. chornic diesease 
general advices :
consult a nutritionist to guide into a better and suitable diet , and drink more fluids  , make sure that your diet contain plenty of health calories , plus , you have to pay attention to dinner meal and dont miss it and make sure that you are not taking any medication causes weight loss as a side effect , and you should exercise regularly and avoid stress and anxiaty