Enzymes can be inhibited through competitive or non-competitive inhibition. Competitive inhibitors resemble the substrate and bind to the enzyme's active site, increasing the Km but not affecting Vmax. Non-competitive inhibitors bind elsewhere on the enzyme, decreasing Vmax but not changing Km. These effects can be seen through Michaelis-Menten and Lineweaver-Burk plots. Many drugs work as competitive inhibitors. Non-competitive inhibition can occur through interfering with cofactors, metal ion activators, or sulfhydryl groups.