How Long Adipex (Phentermine) Stays Your System

Adipex (phentermine) is a medication given to assist people with weight loss. It works by decreasing the appetite and is usually prescribed for three to six weeks to people who are exercising and eating a low-calorie diet.

Phentermine is also the active ingredient in Fastin, Ionamin, and Zantryl and is one of the two ingredients in Qsymia. These medications are the most prescribed diet pills on the market. Also, because they are similar to amphetamines and act as a stimulant, they are a controlled substance and are often sold illicitly.

Knowing how phentermine acts in your system and for how long can help you avoid drug interactions and side effects. It's also important to note that phentermine has the potential to become addicting.

How Long Does It Take to Feel Effects?

Phentermine acts similarly to amphetamines in suppressing the appetite, stimulating the central nervous system, and elevating blood pressure. It is taken as a tablet or an extended-release capsule, with dosage and timing depending on the form. The extended-release capsule is usually taken once per day in the morning, while the tablets are taken a half hour before meals, three times per day.

After a dosage, phentermine is absorbed through the gastrointestinal tract and reaches peak concentrations in the blood in three to 4.4 hours. It has a half-life of about 25 hours, which is the time it takes for half of the dosage to be metabolized by the liver or excreted unchanged in the urine. It takes five to six half-lives for drugs to be almost completely eliminated from your system.

Factors That Affect Detection Time

The amount of phentermine detected in tests and how long it stays in your system is dependent on a number of factors. These include your age, the dose and how long you've been taking it, and your metabolism. For instance, a person of average build and metabolism can expect phentermine to be present in urine for three to five days. It may be faster for someone of a small build or longer for an older person.

Since phentermine has a similar structure to amphetamines, a urine drug screen can test positive for amphetamines. According to a 2016 study, immunoassay drug tests of amphetamines and MDMA often turn up a false positive in urine samples from people who have been taking Adipex. This will signal the need for a confirmatory test, which will then show that it was phentermine and not amphetamine or methamphetamine. The original result will then be ruled a false positive. If you have a prescription for phentermine, you should disclose that to the testing lab so your results can be appropriately interpreted.

How Long Can Adipex Be Detected?

A typical dose of Adipex is one 37.5 mg tablet in the morning before breakfast. This dose is likely to be detected in the urine for one to four days, up to 24 hours in the blood, and up to one month in hair tests. Urine tests are the most common, so it's fairly safe to stop taking Adipex a week before the drug test and expect for it to not show up on the test. Keep in mind that if you are using the drug as prescribed, it is not a problem for it to show up on the test. If you are taking more than the recommended dose and using it off-label, it may stay in your system for longer.

How to Get Adipex Out of Your System

It is recommended to taper Adipex use rather than immediately stop using it. Adipex will generally be out of your system about 2 days after the last time you take it. If you'd like to support your body in eliminating Adipex, drink more fluids, exercise, and increase fat intake. Phentermine is stored in body fat and burning fat supports elimination. All of this having been said, there is no healthy way to speed up this process. If you are expecting to be tested for Adipex, disclose that you are taking it or stop using it prior to being tested. People prescribed Adipex for weight loss often expect to take it for about 12 weeks. Plan ahead.

Symptoms of Overdose

Phentermine has stimulant properties and can increase hormone levels, including dopamine, norepinephrine, and serotonin. This is very similar to amphetamines. For these reasons, prescriptions are tightly regulated and often only allowed for short periods of time. Additionally, it is not recommended for people with a history of stimulant use disorder.

Some of the serious side effects of Adipex include:

If you think someone has overdosed on any phentermine medication, call the poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call 911 immediately.

It is important that you discuss all of your medications and supplements with your doctor to avoid drug interactions. Drugs of special concern include those used to treat depression and similar conditions. This includes monoamine oxidase inhibitors (MAOIs), such as Marplan and Nardil, and selective serotonin reuptake inhibitors (SSRIs), such as Prozac, Luvox, Paxil, and Zoloft. Your doctor should also be made aware of any previous heart conditions, including high blood pressure and arteriosclerosis, or if you have hyperthyroidism. It's also best to avoid using alcohol while taking Adipex as it can make the side effects worse.

Getting Help

Adipex and other phentermine medications may be available by prescription and help with your weight loss goals. However, it is important to realize that there are potential risks involved with taking it. Be sure to have a good discussion with your doctor to see if it's right for you and avoid buying it on the street. If you believe you are at risk for a stimulant use disorder, talk to a professional. Stimulant use disorder affects millions of people each year. You are not alone and there are a lot of different pathways for receiving support.

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Article Sources

  1. National Institute of Health. Phentermine Hydrochloride. U.S. National Library of Medicine: DailyMed. 2017.

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