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Phentermine & Qsymia

On average, Phentermine is used for about three to six weeks, though the FDA has approved its use for up to three months. While the drug is currently only FDA-approved for use for up to 12 weeks though, recent studies have suggested that long-term use of the drug is both effective and safe. Unlike Phentermine, use of Qsymia has been approved for long-term use with the FDA, with a lifetime prescription being approved in cases where the drug is effective.


Despite extensive research, we were unable to find data or information concerning the duration of use for Phentermine or Qsymia outside of the prescribed time-frame. While extensive research exists concerning how long patients are generally prescribed to use the medications in connection with their weight-loss efforts, the same does not exist with regards to non-prescribed use instead of or in addition to use prescribed and monitored by a doctor. In attempting to locate this data, we turned first to medical and scientific studies from sources such as NCBI on both weight-loss and obesity in general as well as on weight-loss drugs such as Phentermine and Qsymia specifically. We reviewed a number of reports, including those published over the last month which suggest that long-term use of Phentermine may, in fact, be safer than the FDA or previous research would suggest. However, while this research path provided us with plenty of data and statistics concerning the prescribed, on-label use of Phentermine and Qsymia, it was ineffective in terms of how patients use the drugs without or beyond their doctor's prescribed duration period.

We next turned to news articles and reports focused both in the medical industry and more generally, in the hope that the topic of off-label use would have been reported on in connection with the growing obesity and/or drug abuse epidemics. While this provided us with information concerning the risks associated with long-term or off-label use of Phentermine and other weight-loss medications, no data were available concerning the number of patients using Phentermine for longer than prescribed.

Finally, we turned to social media and review sites such as Twitter and WebMD in the hopes that patients using Phentermine and/or Qsymia in an off-label manner would share their experiences online. The goal was to learn from these posts about how long patients report taking the drug(s) outside of the officially reported statistics. However, while we were able to find plenty of information concerning patients' personal experience in terms of effectiveness, no significant information was available concerning the duration of use outside of the prescribed time frame.

Very little specific data concerning the duration of use for Qsymia specifically existed. While data has been published concerning weight loss statistics after 12, 28, and 56 weeks, specific statistics on how long the average patient takes Qsymia for was not available despite following each of the above-detailed strategies.

Please note that both Phentermine and Qsymia are indicated exclusively for weight loss. As a result, all data that has been found is related specifically to patients using the drug(s) to lose weight.


The majority of patients get prescribed Phentermine for short-term use, with most taking it for approximately three to six weeks. Ultimately though, "the length of treatment depends on how you respond to the medication." The short-term prescription of Phentermine is partially due to the drug's addictive properties, which dictate that patients should only take the smallest effective dose for the shortest possible period of time. Additionally, though, the drug can cause other serious side-effects such as increased blood pressure and incidences of heart attack, stroke, and death. As a result, the FDA has only approved the use of Phentermine for up to three months.

Despite this though, recent studies have suggested that prolonged Phentermine use can be both safe and effective, with patients reporting greater rates of weight loss when taking the drug for several months up to two years. Specifically, a study published last month by researchers at the Wake Forest Baptist Health and the Patient Outcomes Research to Advance Learning (PORTAL) network compared short-term users of the drug to long-term users and "found that people who stayed on Phentermine longer experienced greater weight loss than those who took the drug for three months or less, and longer-term use was not associated with increases in blood pressure or increased risk of heart attack, stroke or death." Additionally, and despite the FDA's short-term approval for the drug, "physicians have used it successfully for long-term since its initial approval in 1959."


Qsymia is approved for longer-term use than Phentermine, with the drug's website indicating that patients should begin with a two-week prescription and re-evaluate their goals, success, and side-effects with their physician from there. The drug is shown to provide increased rates of weight loss after 12, 28, and 56 weeks, and ultimately it's been approved by the FDA for lifetime use if effective. Specifically, Qsymia is considered a life-long therapy in patients who respond to the drug and tolerate it. That said, the FDA recommends that Qsymia use be stopped or the dosage increased if patients haven't reached a certain threshold of weight loss after three months of use. If, three months later, the rate of weight loss has still not increased, use should be discontinued.