Medications used to help you gain weight are often prescribed for loss of appetite caused by conditions such as cancer, HIV, and other chronic conditions. They work by stimulating appetite and may also reduce nausea. promoting weight gain through different mechanisms. Megestrol (Megace ES) comes as an oral liquid. Dronabinol (Marinol, Syndros) comes in oral capsules or a liquid. Growth hormone analogs, such as somatropin (Serostim), are typically administered as injections. These options provide various ways to help you gain weight gain effectively.