Yes, in some cases homeopathic treatment helps in gaining weight.
It has been seen in many patients that stress is a main hurdle to gain weight. After treating the patient with a right homeopathic constitutional remedy your mind restores health. Once the stress disappears, you will gain weight.
If you are suffering from recurrent infections, homeopathic treatment cures the recurrent disease leading to weight gain in cases where there was weight loss due to recurrent illness.
However, if your body prototype is as what you are, that is in simpler words if you have familial tendency to be thin, no medicine on the earth can help you gaining weight.