It's critical to understand the fact that, being underweight is a condition which happens due to various reasons such as metabolism, diet, and sometimes underlying health issues. In place of injections, discuss your issue with a healthcare expert. They can evaluate your condition and advise you to have a balanced diet filled with healthy calories and doing strength training to add on to your muscles. This approach is comparatively safer, more secure, and sustainable. Remember, you will gain weight slowly from nutritious foods and exercise which will be beneficial for the whole body health. The consultation of a specialist like a physician or a dietician will make you highly successful in your approach. Keep optimism! With the right plan, you can reach the ideal weight!