An antonym for "coughed up" would be something like swallowed or absorbed. When we say "coughed up," we typically mean that something was expelled from the mouth or throat, often forcefully, as in the case of phlegm or mucus. The opposite of this would be for the body to take in or absorb whatever substance is causing discomfort or irritation, without expelling it through coughing or other means. This might be the case for medications, for instance, which are designed to be absorbed by the body rather than expelled. Another antonym for "coughed up" might be something like "held back" or "suppressed," indicating that a cough or other bodily reaction has been deliberately restrained or kept under control.