How Long Does Phentermine Stay in Your System

The length of effects of one drug to another varies. For example, the high from one drug can last up to 30 minutes while the high from another can last up to 8 hours. The same is true for how long a drug stays in your system, even after the effect has subsided. How long a drug is detectable depends significantly on its half-life. The half-life of a drug refers to the time it takes for it to be metabolized by half. In other words, 50% of the drug’s concentration in the body is reduced for every half-life.

For Phentermine specifically, it can be detected on a standard urinalysis test for about 5-6 half-lives. The elimination half-life ranges 19-24 hours under normal conditions; hence it will stay in your system for about 5-6 days.

Illustrative Example of Phentermine’s Half-Life

Taking a 37.5 mg dose of Phentermine with a half-life of 24 hours, the following is true:

  • 24 hours (1 day) after Phentermine administration, 18.75 mg of it remains in your system.
  • 48 hours (2 days) after Phentermine administration, 9.38 mg of it remains in your system.
  • 72 hours (3 days) after Phentermine administration, 4.69 mg of it remains in your system.
  • 96 hours (4 days) after Phentermine administration, 2.34 mg of it remains in your system.
  • 120 hours (5 days) after Phentermine administration, 1.17 mg of it remains in your system.
  • 144 hours (6 days) after Phentermine administration, 0.59 mg of it remains in your system.

While Phentermine’s half-life is very indicative of how long it remains detectable, other factors influence the amount of time it stays in your system. These include the type of test being used, frequency of Phentermine use, body mass, hydration levels, drug tolerance, metabolic rate, and medical conditions that impact Phentermine elimination. All things considered, it’s worth noting that Phentermine’s half-life is but one factor that, in practice, also varies between individuals.

Significance of Phentermine’s Half-Life

The ideal half-life for once-daily dosing of oral drugs is 12-48 hours. Too long of a half-life may pose more withdrawal problems while too short of a half-life may pose safety challenges. In the case of Phentermine, it’s half-life is neither too long nor too short. Moreover, the half-life of Phentermine plays a crucial role when it’s time to stop taking it. Along with the strength and duration of Phentermine, the doctor will consider its half-life. This is important so that you will not quit cold turkey and risk unpleasant withdrawal symptoms.

Phentermine’s Administration and Dosage

Phentermine is intended as a short term (a few weeks) complement in a regimen of caloric restriction and weight reduction. The usual pediatric dose for obesity is 8 mg taken orally three times a day before meals. It is not recommended for use in pediatric patients who are 16 years old and below.

The usual adult dose of Phentermine is 37.5 mg as prescribed by the doctor. It should be administered in the morning, with or without food. To administer, gently remove one tablet from the bottle with your dry hands. Then, place it immediately on top of your tongue where it will dissolve, and swallow with or without water.

Note: Avoid administering Phentermine in the late evening as this can result in insomnia.

Phentermine’s Metabolism

The kidneys primarily excrete the weight loss drug. As mentioned, Phentermine’s half-life in your body is around 19-24 hours and is slightly influenced by urinary pH. The half-life will decrease to about 7-8 hours in an acidic environment. After administration of Phentermine, most absorption occurs from your small intestine. The duration of action after Phentermine pediatric dose administration is 4 hours and 12-14 hours for adult dose administration.

Phentermine and Drug Test

Drug testing is an action that helps prospective employers determine if job candidates are using illicit substances or have been abusing prescription medication. Employers also prescribe workplace or pre-placement drug tests for employees who are returning to work after a leave of absence or after an injury. The goal of employers in taking this action is to create a safe working environment for the employees. Not only does workplace drug testing help employees deter from taking drugs, but it also identifies and helps employees with their drug problems.

Drugs that have been introduced in the body can be detected through several tests including Urine Testing, Hair Testing, Oral Fluid Testing, Synthetics Testing, Expanded Opioid Testing, and Evidential Breath Alcohol Testing (EBAT). By far, though, the most commonly used drug test is Urine Testing. During a urine drug testing, a person will have to urinate into a specimen bottle, and a supervisor will watch the urine collection. The specimen will then be examined whether or not it contains the following illegal substances:

  • Cocaine: coke, crack
  • Opiates: heroin, opium, codeine, morphine
  • Methamphetamines: meth, ecstasy, crank, meth
  • THC: marijuana, cannabinoids, hash
  • Phencyclidine: PCP, angel dust

Although Phentermine is not an amphetamine, there are cases when it gives a false-positive result during a drug screening urinalysis. This is because the chemical structure of Phentermine is similar to that of amphetamine. However, in the event of a positive result, the medical review officer will review medical or other reasons for the result. As long as you can provide a Phentermine prescription from your doctor, a false-negative is nothing to worry about. To be on the safe side, do not take more than the recommended dosage as this might raise questions for the medical review officer.

In anticipation of a drug test during your Phentermine prescription, inform your direct supervisor about it and provide evidence of the prescription. This will save you from explaining yourself after a false positive reading. But, if you are not comfortable disclosing that you are taking Phentermine, you may consider not taking Phentermine for a few days. With regards to Phentermine’s half-life, the last dose should not be detectable in your urine after 6-7 days.

Phentermine Alternatives

The safest method to avoid a false-positive reading due to Phentermine is to take alternatives such as PhenGold, PhenQ, and Phen375. Without the ingredients similar to Phentermine, these alternatives will not show up on an employment drug testing:


PhenGoldPhenGold is the leading weight-loss supplement that’s formulated to suppress appetite, raise metabolism, and boost energy levels. According to the makers of the supplement, people who are struggling with obesity and weight gain can benefit from it as PhenGold promotes a fitter and slimmer figure.

The organic and fat-burning ingredients unique to PhenGold are capsicum extract, caffeine, green coffee, green tea leaf extract, vitamins, Dimethylaminoethanol, L-Theanine and L-Tyrosine, Rhodiola Rosea, and BioPerine black pepper. The presence of vitamin B6 is responsible for the reduced pangs of hunger and a steep reduction in food cravings.

All the ingredients in PhenGold are clinically proven safe and effective. Overall, users found the ingredients to work together in doubling down their body’s natural ability to burn fat. One user testified that she gained desirable results after 4 weeks of using the formula and lost a resounding 30 lbs.

With PhenGold, there’s absolutely nothing to lose or risk as it’s inexpensive and comes with a full 100% money-back guarantee. It combines all the benefits of multiple weight-loss products, hence, a win-win situation.


Buy PhenQ AustraliaPhenQ is the ultimate 5-in-1 weight loss pill that uses the highest quality, natural ingredients prepared in FDA and GMA approved labs. It targets weight loss by burning fat, stopping fat production, suppressing the appetite, boosting energy, and improving mood.

The key ingredients that make PhenQ so effective are capsimax powder, Chromium Picolinate, caffeine, nopal, and L-Carnitine fumarate. Besides, PhenQ contains a secret ingredient called a-Lacys Reset that is scientifically approved to encourage excellent fat-burning results. Unlike other weight loss products, PhenQ’s active ingredients are backed up by scientific research that has proven the superior fat-busting results of the formula.

In Australia, PhenQ is considered the second most potent fat-burning formula. It guarantees a rapid speed of weight loss. Additionally, PhenQ is on point with its working so its takers can expect to lose up to 12 lbs in 4 weeks.

PhenQ makes losing weight straightforward, and it is more than just a pill when combined with diet and exercise.


Phen375This natural dietary product helps boost one’s fitness levels. An FDA compliant facility develops it; therefore, it has pharmaceutical quality. It works by suppressing hunger and getting the body into a state of burning fats for energy.

This product contains high-quality ingredients in relevant quantities that help reduce calories and boost the body’s metabolism. These include L-carnitine, caffeine powder Anhydrous, Coleus Forskohlii Root PE (10% Forskolin), Citrus Aurantium, cayenne pepper, and Dendrobium Nobile Extract (from orchids).

Regular use of Phen375 helps amplify the weight loss process. It can be paired with a regular diet and workout. Accordingly, PhenGold allows the body to burn fat 24 hours a day. User’s experiences concluded that it enables a weight loss average of 3-5 lbs per week.

Phen375 is meant to lose the extra pounds that have been making people lose their self-esteem. More than anything, it guarantees retention of muscle mass despite the fat loss.