I do not recommend any artificial weight gainers. Generally one should not crave for wt gain unnaturally. Instead, appetite, digestion,
metabolism should be corrected first. If these functions are normal, optimum weight will be gained by the body.
However some herbs categorised under 'Brunghnadi Varg' herbs are used for nutrition purpose. These, in turn, add weight to the extent naturally required by the body. However still some things like milk boiled with dates, dried grapes etc help in gaining weight. But metabolism and digestive system should be in sound condition.
To achieve this, light food, active routine, long walks,
Yoga exercises, deep breathing will help. Then some Agnipradeepak i.e. appetite flaring and gut cleansing medicines in Ayurveda like Agnitundi, chitrakadi vati etc are used. These secrete enzymes naturally and all the food start assimilating well and nourish all the seven elements e.g. Rasa, 'rakta', Maansa......up to Shukra . At this point of time Brunghnadi varg of herbs act best. The cycle takes 2 months approx.
The results achieved are long lasting and safe, no side effects, purely natural. What else one should need? Optionally one can always switch to synthetic, toxic and harmful artificial foods and drugs for little quicker results.
Hope this helps you. Ayurveda doctor may be consulted anywhere or through HCM.
My wishes.