https://www.sciencedirect.com/topics/nursing-and-health-professions/epinephrine

Pharmacokinetics

Adrenaline (epinephrine) is well absorbed from IM and SC sites; absorption can be enhanced by massaging the injection site and absorption is slightly faster from IM sites compared to SC. Onset of action after IV administration is immediate and after SC administration within 5–10 min. Oral administration is not effective as it is rapidly metabolized in the gut. Adrenaline (epinephrine) crosses the placenta and enters milk but does not cross the blood–brain barrier.