Gaining weight works by putting more fuel into your body than you use. That's physically the only way, there is no way to synthesize energy. Because of caloric

Gaining weight works by putting more fuel into your body than you use. That's physically the only way, there is no way to synthesize energy. Because of caloric density limits, there is no substitute for putting a certain amount of stuff in your body. A pill can physically not contain enough calories. There are options around that, but that depends on what's driving your personal energy deficit. What's the job that the weight gain intervention needs to do for you, that whatever you try to eat right now does not? What's motivating your current diet? Are you for example disgusted by swallowing anything at all? Are you more partial to liquids than whole foods? Do you dislike sugar in particular?