A fusion inhibitor is a class of antiretroviral drugs used to treat viral infections such as HIV. It works by blocking the virus from fusing with a cell's membrane to enter and infect the cell.
For example, HIV binds to host cell receptor CD4 by the protein gp120. Upon binding GP120 deforms allowing the viral protein gp41 to embed itself into the host cell's plasma membrane, entry inhibitors bind to GP41 preventing the creation of an entry pore for the capsid of the virus keeping it out of the cell. [1]
It has been found that a component in green tea, EGCG, competes for gp120, and Theaflavins found in black tea competes for gp41 with HIV.