Orlistat or tetrahydrolipstatin (Xenical, Hoffmann-La Roche) is a saturated derivative of lipstatin originally isolated from Streptomyces toxytricini. Orlistat (Xenical, Hoffmann-La Roche) is a powerful inhibitor of gastrointestinal lipase and as such, reduces fat absorption. Orlistat acts by binding covalently to the serine residue of the active site of gastric and pancreatic lipases. When administered with fat-containing foods, orlistat partially inhibits hydrolysis of triglycerides, thus reducing the subsequent absorption of monoaclglycerides and free fatty acids. Unlike other weight-reducing drugs it is minimally absorbed and has no effects in the CNS. Xenical is indicated for obesity management including weight loss and weight maintenance when used in conjunction witha reduced-calorie diet. XENICAL is also indicated to reduce the risk for weight regain after prior weight loss. XENICAL is indicated for obese patients with an initial body mass index (BMI) ≥ 30 kg/m2 or ≥ 27 kg/m2 in the presence of other risk factors (eg, hypertension, diabetes, dyslipidemia). In addition to its well established efficacy in achieving modest weight loss, orlistat has been shown to improve glycaemic parameters in obese adults with type 2 diabetes mellitus as well as some features of the metabolic syndrome.

Fenfluramine (former brand names Pondimin, Ponderax and Adifax), also known as 3-trifluoromethyl-N-ethylamphetamine, is an anorectic that is no longer marketed. In combination with phentermine, it was part of the anti-obesity medication Fen-phen. Fenfluramine was introduced on the U.S. market in 1973 and withdrawn in 1997. It is the racemic mixture of two enantiomers, dexfenfluramine, and levofenfluramine. The drug increases the level of serotonin, a neurotransmitter that regulates mood, appetite and other functions. Fenfluramine causes the release of serotonin by disrupting vesicular storage of the neurotransmitter and reversing serotonin transporter function. The drug was withdrawn from the U.S. market in 1997 after reports of heart valve disease and pulmonary hypertension, including a condition known as cardiac fibrosis. It was subsequently withdrawn from other markets around the world. In this small exploratory and retrospective study, remarkably good results were reported on the use of fenfluramine as an add-on medication for controlling seizures in patients with the Dravet syndrome. The side effects were rare and nonserious and did not result in termination of the treatment. It is possible that this drug may have anticonvulsive effects for other severe epilepsy syndromes, especially in those characterized by photosensitive or induced seizures.

Phentermine is an amphetamine that stimulates neurons to release or maintain high levels of a particular group of neurotransmitters known as catecholamines; these include dopamine and norepinephrine. High levels of these catecholamines tend to suppress hunger signals and appetite. The drug seems to inhibit reuptake of noradrenaline, dopamine, and seratonin through inhibition or reversal of the reuptake transporters. It may also inhibit MAO enzymes leaving more neurotransmitter available at the synapse. Phentermine (through catecholamine elevation) may also indirectly affect leptin levels in the brain. It is theorized that phentermine can raise levels of leptin which signal satiety. It is also theorized that increased levels of the catecholamines are partially responsible for halting another chemical messenger known as neuropeptide Y. This peptide initiates eating, decreases energy expenditure, and increases fat storage. Phentermine is indicated in the management of exogenous obesity as a short term (a few weeks) adjunct in a regimen of weight reduction based on caloric restriction. Phentermine hydrochloride is a sympathomimetic amine with pharmacologic activity similar to the prototype drugs of this class used in obesity, the amphetamines. Actions include central nervous system stimulation and elevation of blood pressure. Tachyphylaxis and tolerance have been demonstrated with all drugs of this class in which these phenomena have been looked for.

Mitratapide is a potent inhibitor of the microsomal triglyceride transfer protein used for the treatment of obesity in dogs. The drug was developed by Janssen Pharmaceutica and is chemically related to the antifungal drugs such as itraconazole which were also developed by Janssen. Administration of mitratapide to dogs results in reduced uptake of dietary lipids, dose dependent decreases in serum cholesterol and triglyceride and an increased presence of triglyceride containing droplets in enterocytes. Mitratapide also has a slight appetite decreasing effect that is claimed to be associated with its mode of action. Vomiting, diarrhoea or softened stools may occur during treatment. In most cases, these effects are mild and transient.

Lorcaserin, currently marketed under the trade name Belviq and previously Lorqess during development, is a weight-loss drug developed by Arena Pharmaceuticals. Lorcaserin is a selective 5-HT2C receptor agonist, and in vitro testing of the drug showed reasonable selectivity for 5-HT2C over other related targets. 5-HT2C receptors are located almost exclusively in the brain, and can be found in the choroid plexus, cortex, hippocampus, cerebellum, amygdala, thalamus, and hypothalamus. The activation of 5-HT2C receptors in the hypothalamus is supposed to activate proopiomelanocortin (POMC) production and consequently promote weight loss through satiety. This hypothesis is supported by clinical trials and other studies. While it is generally thought that 5-HT2C receptors help to regulate appetite as well as mood, and endocrine secretion, the exact mechanism of appetite regulation is not yet known. Lorcaserin has shown 100x selectivity for 5-HT2C versus the closely related 5-HT2B receptor, and 17x selectivity over the 5-HT2A receptor

Mazindol is an amphetamine-like medicine which was developed by Sandoz in 1967 and approved by FDA for the treatment of obesity and Duchenne muscular dystrophy under the names Sanorex and Mazanor. The exact mechanism of action is unknown, but possibly involves the stimulation of beta-adrenergic receptors and inhibition of monoamine reuptake. Both Sanorex and Mazanor were withdrawn from the market by reason other than safety. NLS Pharma now is developing mazindol for Attention Hyperactivity Disorder in adults (phase II).

Cathine, known as D-norpseudoephedrine, is a psychoactive drug of amphetamine class, found naturally in Catha edulis (khat). It is a norepinephrine and dopamine releasing agent, and has thermogenic and anorectic effect. In the United States, cathine is classified as a Schedule IV controlled substance. Cathine hydrochloride is used as an appetite suppressant during the first few weeks of dieting to help establish new eating habits.

Clobenzorex is a central stimulant and sympathomimetic used as an anti-obesity drug; an n-substituted amphetamine, which is metabolized to amphethamine. Its actions are like those of dexamphetamine and has been used as a drug of abuse.

Etilamfetamine (Apetinil) is a stimulant drug of amphetamine chemical class. It is an N-substituted amphetamine with an ethyl group on the amphetamine backbone. It was used as an anorectic or appetite suppressant. Etilamfetamine is a psychoactive drug, which can be used as a recreational drug. Etilamfetamine has been abused as a “designer drug” alternative to amphetamine and possibly methamphetamine. It is a dopamine releasing agent.

Dirlotapide is indicated for the management of obesity in dogs. Dirlotapide is a microsomal triglyceride transfer protein (MTP) inhibitor. It mainly acts locally in the gut to reduce appetite, increase fecal fat and produce weight loss in dogs. The adverse reactions associated with treatment with Dirlotapide include vomiting, loose stools/diarrhea, lethargy, and anorexia.