Hydroxychloroquine (HCQ) is an antimalarial drug that inhibits autophagy and is used to treat systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). It exhibits immunomodulatory, antithrombotic, and antiplatelet properties. It inhibits the release endothelin-1, a potent vasoconstrictor, and restores impaired angiogenesis in TNF-α-treated endothelial cells in vitro. It also reduces the production of inflammatory cytokines such as TNF-α, IFN-γ, and IL-6 from peripheral blood mononuclear cells, upregulates IL-10 and decreases platelet aggregation.