Hi,
Thanks for using Healthcaremagic,
You are young 25 year and 45 kg I presume you are
underweight as you have not mentioned your height.
If you do not have any other problem then high calories and protein diet helps to gain weight along with muscle building exercises.
It will take some time to gain weight it can not be done in short period please take frequent meals.
Food items which help in such cases are red meat if you take nonveg, Peanut butter,whole milk, fruits like mango,banana,papaya,whole wheat bread,butter,Peanuts,almonds,walnuts.Cheese,Potatoes are some food item which helps to gain weight.
This diet should be combined with exercise including weight lifting. You can take help of local Dietitian and Gym trainer.
Drugs like
steroids anabolic should not be used unless indicated and prescribed by doctor.
You can visit local Physician for complete medical evaluation.
Hope this helps.
Good Luck.
Take care.
Dr.Akhilesh Dubey M.D