The drug must find it way to the target cells typically after administration by injection into the skin, muscle, bloodstream or cerebrospinal fluid, or by the gastrointestinal route passing through both hydrophobic and hydrophilic biological environments

It must be directed toward the target cells without significant interaction with non-target tissues and avoiding attack by the immune system.

The drug must be taken up by the target cells through active or passive endocytosis, be released by the endosome, avoid destructive nucleases, and sometimes reach the cell nucleus.

Finally, the drug gets processed by cellular machinery.