Do Weight Loss Pills Show Up On Drug Tests

Weight loss pills refer to a wide spectrum of ingredients that can help treat obesity. Those ingredients may include, for example, phentermine drug, as well as natural ingredients, such as glucomannan, garcinia cambogia extract, and Oolong tea extract. Phentermine drug is derived from amphetamines, which makes it commonly misused. Examples of other drugs containing phentermine and are sometimes known as weight loss pills include Oby-Cap, Suprenza, T-Diet, Fastin and Lonmin.

How do weight loss pills work

Weight loss pills work through different mechanisms of action, depending on what ingredients they contain. In regards to phentermine-containing weight loss pills, those pills work as follows,

  • Decreasing hunger-signals
  • Stimulating the central nervous system, causing it to increase the levels and maintain high levels of vital hormones, including dopamine, norepinephrine, and serotonin. The higher those hormones are, the less you feel hungry.

How long do weight loss pills stay in your system

Up to 7.75 days since the last dose, phentermine-containing pills are likely to stay in your system. The reason is that the half-life of phentermine ranges from 16 to 31 hours, which means that within 16-31 hours post-administration, 50% of the dose will no longer be active in your system, and so on till the full dose is eliminated.

Surely, that duration differs, in case of administering weight loss pills containing other substances. Furthermore, other factors can significantly affect the duration phentermine-containing weight loss pills stay in your system. Those factors differ from a person to another, including:

  • your age
  • your body mass
  • the administered dose
  • whether you’re a mild or a chronic user of weight loss pills
  • Your metabolic rate of drugs. That determines how quickly your system can get rid of phentermine.

Will weight loss pills show on a drug test?

Yes, phentermine-containing weight loss pills will show positive on a drug test, specifically the test of amphetamines. However, other factors can affect the tests’ results. Those factors can even cause the test to be negative, including:

  1. The type of the test you are required to undergo
  2. the time the test is performed. Each test has a certain time frame, within which the test can detect a certain drug.
  3. Individual factors that differ from a person to another, as shown above.

How long are weight loss pills detectable

Urine, blood, and saliva

Within minutes post-administration, and up to 24 hours, phentermine-containing pills are likely detectable in your blood; while in urine, phentermine is likely detectable for up to 3-4 days.

Hair, saliva and fingernails

While fingernails are rarely considered for phentermine testing; hair is considered the best medium, as it helps detect the presence of phentermine in the system for a long time. Up to 1 month and sometimes longer, phentermine is likely detectable in hair. Regarding saliva, starting from 1 hour and up to 2 days post-administration, phentermine may be detected.

What drug tests will show the presence of weight loss pills in the system

  • Blood analysis
  • Urinalysis, such as high-performance liquid chromatography (HPLC)
  • Hair-based tests, including Gas chromatography/mass spectrometry, ELISA (enzyme-linked immunosorbent assays)
  • Saliva-based tests, such as high-performance liquid chromatography (HPLC)

How are weight loss pills stored in the body

After administration, phentermine is absorbed from the gastrointestinal tract, rising in blood till achieving a peak level in plasma within 3 to 4.4 hours. Afterward, within the previously-mentioned half-life, phentermine is eliminated.

Certain factors can affect the storage of phentermine in the system, including, for example, the concomitant use of drugs, as well as your diet. If you’re concomitantly taking other drugs that can/or if your diet can cause your urine to be more alkaline than usual, in this case, phentermine may tend to be stored for a longer time in the system.

On the other hand, in case your diet or the drugs you’re concomitantly taking cause your urine to be more acidic than normal, phentermine will be quickly eliminated from your system.


  1. PubChem. Phentermine.
  2. PubChem. Amphetamine.
  3. Pubchem. Dextroamphetamine.

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