Hello doctor, i am 25 and my weight is 48. i am underweight

Patient: Hello doctor, i am 25 and my weight is 48 kg, i think its really under weight i want to gain the weight, i dont have time to go for fitness, i go for work everyday for 8 hours, the work is physical work. And my legs are too skiny, please advice me the right and effective medicine to gain the weight fast and get big legs, thank you for your help, looking forward for your response.

Doctor: Hello.Welcome to Ask The Doctor.I understand your concern.Following are the causes of weight loss or not able to gain weight at your age:1. Malabsorption syndrome.2. Inadequate diet3. Intestinal Tuberculosis.4. Normal constitution of the body.5. Hyperthyroidism.I would advise following in such scenario:1. To get anti-TTG Antibody test done to rule out Malabsorption syndrome like Celiac disease.2. Upper GI endoscopy3. Ultrasound Abdomen.4. Chest Xray5. Thyroid profile6. Hemogram with ESR.Share my opinion with your Doctor.I hope it helps.Stay Healthy