Bioavailability
The share of a drug that reaches the bloodstream; lower for oral GLP-1s than injections.
Bioavailability is the proportion of an administered dose that actually reaches systemic circulation and can have an effect. Injected GLP-1s have high bioavailability, while oral semaglutide (Rybelsus) has much lower oral absorption, which is why it must be taken on an empty stomach with specific timing and why its weight effect at approved doses is generally more modest than the higher injectable weight-management doses.