Drugs used for weight loss are generally called anorexiants. All the drugs are potentially effective when used appropriately and with additional weight loss measures, including exercise and behavioral modification. The long-term effects of most of these medications have not been established. Most lose their effectiveness over time, thus requiring increased dosage, and they can be addictive and dangerous.

None of these drugs deals with the underlying problems that may be causing obesity. Unless specifically instructed by a physician, people should use non-drug methods for losing weight. Except under rare circumstances, pregnant or nursing women should never take diet medications of any sort, including herbal and over-the-counter remedies.

Over-the-Counter Drugs and Herbal Remedies
A 2001 study reported that 7% of American adults use nonprescription weight-loss products. People must be cautious when using any weight-loss medications, including over-the counter diet pills and herbal or so-called natural remedies. Buying unverified products over the Internet can be particularly dangerous. For example, a product that has been withdrawn, Lipokinex, contained chemicals that caused liver damage. The following are examples of other weight-loss products that have been associated with some harm or are not effective:

 
• Over-the-counter diet pills, such as Acutrim or Dexatrim, contain phenylpropanolamine or PPA. They have been removed after some reports of severe high blood pressure and stroke.  
• A number of over-the-counter remedies (Herbal Phen-Fen, PhenTrim, Phen-Cal, Xenadrine) contain ephedrine, derived from the ephedra (also known as Ma Huang) herb. Ephedrine is actually a component in adrenaline and can cause a number of side effects, including infrequent cases of severe effects (rapid heartbeat, high blood pressure, psychosis, heart attacks, and seizures). Pseudoephedrine, an ingredient commonly found in many antihistamines, has similar effects and is sometimes used by dieters.  
• Over-the-counter products containing tiratricol, a thyroid hormone, have been sold for weight loss. Such products may increase the risk for heart attack and stroke.  
• Chitosan, a dietary fiber from shellfish does prevent a little fat from being absorbed in the intestine, but limited studies have not found that it contributes to weight loss.  
• Many dietary herbal teas contain laxatives, which can cause gastrointestinal distress, and, if overused, may lead to chronic pain, constipation, and dependency. In rare cases, dehydration and death have occurred. Some laxative substances found in teas include senna, aloe, buckthorn, rhubarb root, cascara, and castor oil.  
• Some fiber supplements containing guar gum have also caused obstruction of the gastrointestinal tract.  
• Dietary remedies that list the ingredient plantain may contain digitalis, a powerful chemical that affects the heart. (This should not be confused with the harmless banana-like plant also called plantain.)

Orlistat
Orlistat (Xenical) can help about one-third of obese patients with modest weight loss, and can assist in long term maintenance of weight loss. It reduces the body’s absorption of fat from foods, thereby reducing weight and cholesterol. Orlistat blocks the action of lipase, an enzyme in the intestine that breaks down fat. In carefully selected patients, studies have reported an average of 5% to 10% drop in body weight after a year’s use. Such patients, however, were part of clinical studies. It does not work for all patients, however. In one survey of patients who took it, 10% gained weight or did not lose any and 43% lost less than 5%.

Evidence is suggesting that the drug has other health benefits. The drug appears to have particular benefits for people at risk or who have type 2 diabetes. Orlistat may delay or prevent its onset and slow progression in people who already have diabetes. It may also improve cholesterol levels, regardless of weight loss.

The drug can cause gastrointestinal problems and may interfere with absorption of the fat-soluble vitamins A, D, and E and other important nutrients. The most unpleasant side effect is oily leakage of feces from the anus. Restricting fats can reduce this effect. People with bowel disease should probably avoid it.

Sibutramine
Sibutramine (Meridia) keeps two important brain chemicals, serotonin and norepinephrine, in balance, which helps to increase metabolism. It causes a feeling of fullness and increases energy levels. Studies indicate that sibutramine is effective in achieving weight loss although it slows considerably after the first three months. agent also appears to improve cholesterol and lipid levels and have other effects that may benefit the heart. There have been reports, however, of increases in heart rate and blood pressure, although a 2001 study reported stable blood pressures in people who took it for 48 weeks.

Side effects are common. They include dry mouth, constipation, and insomnia, and in one study almost half the patients dropped out because of them. At this time, people who have a history of high blood pressure, stroke, heart disease, or arrythmias should not take this drug. People taking decongestants, bronchodilators (such as for asthma), monoamine oxidase inhibitors, or serotonin reuptake inhibitors should also avoid sibutramine.

Amphetamines
The amphetamines dextroamphetamine (Dexedrine), methamphetamine (Desoxyn), and phenmetrazine (Pleudin) were used most often in the past but are no longer prescribed for weight loss. These drugs elevate mood and produce some modest weight loss over the short term, but present serious risks of addiction, agitation, and insomnia.

Sympathomimetics
Sympathomimetics are agents that act like the neurotransmitter norepinephrine (a stress hormone). Less addictive and possibly safer than amphetamines, these drugs still raise blood pressure. They are approved for short-term use and include phentermine (Ionamin, Adipex, Fastin), diethylpropion, benzphetamine (Didrex), and phendimetrazine (Adipost, Bontril, Melfiat, Plegine, Prelu-2, Statobex).

Phentermine achieved weight loss of 8.1% in one study, which was better than either sibutramine (5%) or orlistat (3.4%). In the same study diethylpropion achieved no weight loss. In fact phentermine has been withdrawn from the UK market but not the US.