Although Adderall and phentermine are both stimulant medications, they are intended to be used for two very different purposes. Phentermine, the active ingredient of the brand name medication Adipex-P, is approved for use in weight loss. Adderall, the brand name for the combination of amphetamine and dextroamphentamine, is typically prescribed to treat attention deficit hyperactivity disorder or narcolepsy. However, a common side effect of Adderall is weight loss, so this medication is also sometimes prescribed "off-label" as a weight-loss aid. Do your research and talk to a doctor to determine if either of these medications is appropriate for your situation.
When determining which medication to use, it is important to consider the purpose for which the medication was intended. Phentermine is approved as a weight-loss medication by the U.S. Food and Drug Administration. To get FDA approval, the medication underwent rigorous testing for effectiveness and safety to be used for that purpose. Adderall, on the other hand, has not been approved by the FDA for the purpose of weight loss. Because the medication did not have to undergo the same rigorous testing as phentermine, there may be unknown risks associated with using Adderall for this purpose. It is generally considered safer to use medications for their intended purpose.
Phentermine is the active ingredient of many different weight loss medications, while Adderall is a specific brand itself. It is difficult to compare the effectiveness of the medications since the effectiveness of phentermine can depend on the specific brand you're taking. However, in clinical trials, adults with obesity treated with an anorectic drug like phentermine tend to lose more weight on average than those treated with placebo and diet, according to Drugs.com. Clinical studies involving Adderall also may lend some insight as to the drug's effectiveness. Weight loss occurred in 11 percent of adults over the age of 18 taking Adderall in clinical studies. However, it is important to keep in mind that your specific results in taking either of these medications may be different. It is impossible to predict how your body will react to either medication.
Both Adderall and phentermine may cause adverse side effects. In addition to weight loss, Adderall also has many other potential side effects, including rapid or uneven heartbeats, insomnia, increased blood pressure, lightheadedness, tremors, muscle twitches, hallucinations, dizziness, headaches, constipation, diarrhea, changes to mental state and sexual dysfunction. Common side effects of phentermine include diarrhea, constipation, unpleasant taste, dry mouth or vomiting. Both medications may also be habit-forming and lead to physical dependency if taken for too long a time.
When in doubt, it is probably better to take phentermine for weight loss since the medication is intended for that purpose. However, if you have symptoms of attention deficit hyperactivity disorder and also want to lose weight, Adderall may be the better choice. Do your own research of each medication, but always ask your doctor's advice about which medication would be more appropriate for your situation. In addition, consider exploring nonmedical weight loss strategies as well, such as making dietary changes, getting counseling or increasing your exercise routine. These weight-loss techniques may be just as effective as medication and do not come with the same risks of side effects.