Adolescent gynecomastia resolves without treatment in a majority of cases within about two years of onset; adult gynecomastia that has persisted past that window almost never resolves on its own, and no medication reliably shrinks established glandular tissue. What medication can sometimes do is stop the growth by treating a cause that is still active, such as a hormonal imbalance or a triggering drug. The variable that matters most is time: tissue that is new is tissue that may still leave.
Common, hormone-driven, and usually temporary: a majority of pubertal cases settle within about two years. The default is watchful waiting, not intervention. Persistence well past that window moves it into the adult category.
Steroid or hormone use, certain medications, significant weight change, or an underlying condition. Remove or treat the cause early and recent growth can regress. The longer the tissue has been established, the less it gives back.
Tissue that has been present for years is stable: it neither grows dramatically nor leaves. Diet does not touch it, training does not touch it, and waiting has already been tried. Removal, if wanted, is surgical.
A site that arranges surgery telling you to rule surgery out first is not being modest, it is being accurate. If the tissue is recent, get the cause looked for: a blood panel and a medication review are cheap, and treating an active cause is the one non-surgical path that genuinely works. If the pinch test says fat rather than gland (how to tell), the answer is body composition, not an operation. Surgery earns its place only in the remainder: established gland, cause handled, still unwanted. That remainder is real, and for it the operation and its trade-offs by grade are at /conditions/gynecomastia/grades/.