About Prescription Diet Pills

Many people believe that approval by a Food and Drug Administration means that a diet pill is safe and effective. That is not necessarily true. Most prescription diet pills are controlled substances that can cause dependence, and most are only approved for a few weeks' worth of use. They are safer than over-the-counter pills in that they are regulated and inspected, and because they are prescription, you must be under a doctor's care to use them. But they are not magic bullets, and they are not as safe as candy.

Appetite Suppressants

Most prescription diet pills are simply appetite suppressants -- the most common ones are phendimetrazine, phentermine and diethylpropion. All three of these drugs are stimulants, and can make your body react the same way it does to high doses of caffeine. You may experience nervousness, dizziness and a disturbance of your sleep cycle. These drugs are also controlled substances, so you must keep them out of the reach of others. Appetite suppressants are only FDA-approved for use up to 12 weeks, so a longer course would be considered off-label.

Fat Blockers

Orlistat is the only FDA-approved fat blocker available as of time of publication. It works by disabling the digestive enzyme that breaks down fat, so most of the fat you eat passes through unabsorbed. This can increase the amount of weight you lose on a diet and exercise plan. Orlistat is also available over-the-counter at half the prescription strength as Alli. There is one caveat to both drugs -- the makers recommend you consume no more than 15 g of fat at any meal. If you go over, you may experience oily anal leakage. In rare cases, liver damage has been reported in people who have used Orlistat.

Depression Medication

Sometimes, doctors prescribe antidepressants to help people lose weight. According to a 2005 paper in the Prague Medical Report , selective serotonin reuptake inhibitors cause weight loss after about six months, but the weight eventually returns. The researchers found that a year's treatment with bupropion and tianeptine caused lasting weight loss. It is theorized that after treatment with antidepressants, people are more likely to adhere to a healthy eating and exercise plan. In diabetics, the drugs may actually lower blood glucose levels, which can assist with weight loss. The FDA has not approved any antidepressants for use as weight loss drugs, so this application is considered off-label.

Other Off-Label Medication

Some treatments for other conditions have been found to cause weight loss as a side effect, so doctors occasionally prescribe them off-label to treat obesity. Anti-seizure medications zonisamide and topiramate are two such drugs, as is the diabetes medication metformin. None of these drugs are approved for weight loss by the FDA, so there is no data regarding how long they may be used or the dose required to assist with weight loss without causing undesirable side effects. These drugs should only be used under a doctor's close supervision.