Drugs to treat obesity can be divided into three groups: those that reduce food intake; those that alter metabolism; and those that increase thermogenesis. Monoamines acting on noradrenergic receptors, serotonin receptors, dopamine receptors, and histamine receptors can reduce food intake. A number of peptides also affect food intake. The noradrenergic drugs phentermine, diethylpropion, mazindol, benzphetamine, and phendimetrazine are approved only for short-term use. Sibutramine, a norepinephrine-serotonin reuptake inhibitor, is approved for long-term use. Orlistat inhibits pancreatic lipase and can block 30% of the triacylglycerol hydrolysis in subjects eating a 30% fat diet. The only thermogenic drug combination that has been tested is ephedrine and caffeine, but this treatment has not been approved by regulatory agencies. In clinical trials other drugs that may modulate peptide-feeding systems are being developed.