If you are taking phentermine or Adipex, you may be curious about how long this medication will stay in your system.

All medications will remain in your system for a certain amount of time. Some are processed quickly, while others take longer to leave your body.

Certain ways of testing are also more sensitive at picking up phentermine and other substances, such as hair or blood tests.

Continue reading to learn more about phentermine, how long it stays in your system and the addictive properties of this medication.

Facts about phentermine

weight loss

What is phentermine?

Phentermine, also known as Adipex or phenyl-tertiary-butylamine, is a prescribed medication that is used as a weight loss aid for people with a medical requirement to lose weight. [1]

It comes in pills or capsules which should be taken as directed by your medical physician.

Phentermine can suppress your appetite and stop you from feeling hungry – however, these effects may decrease after using this medication for a few weeks.

You should only use phentermine on a short-term basis, as it is extremely addictive.

Do not use phentermine if you suffer from any of the following conditions:

  • Heart problems
  • An overactive thyroid
  • Glaucoma
  • High blood pressure
  • Coronary artery disease
  • A history of drug addiction

Phentermine is similar to amphetamines as it can speed up your body’s natural functions. As a result, it has the potential to be highly addictive and should only be used when prescribed by a doctor.

What is phentermine used for?

Phentermine can be prescribed by a medical professional to treat obesity as it has been found to be an effective weight loss aid.

This medication is not used for superficial weight loss – it should only be considered if you have a medical need to lose weight.

If you have high cholesterol or diabetes and need to lose weight for medical reasons, you may be prescribed phentermine.

You will also be given a diet and exercise plan to follow in addition to taking phentermine regularly.

Some people take phentermine illegally, without a prescription. This can be extremely dangerous and is never advised.

How does phentermine work?

Phentermine can help you to lose weight by suppressing your appetite and stopping you from feeling hungry.

As a result, you are likely to eat less without the uncomfortable pangs of hunger commonly associated with dieting.

Phentermine causes your brain to release a larger amount of certain chemicals on a more frequent basis. These include dopamine, serotonin and norepinephrine which are commonly known as the ‘happy chemicals.’

Having high levels of these chemicals in your brain can reduce your appetite and help you to eat less.

When combined with exercise and a healthy diet plan, many people will begin losing weight fairly quickly.

What are the potential side effects of phentermine?

Phentermine can cause both common and severe side effects, which may be uncomfortable and unpleasant at times. [2]

You should speak to your doctor immediately if you experience any of the following severe side effects:

  • Pain in your chest
  • Swollen feet or ankles
  • Skipped heartbeats, a pounding heart or fluttering in your chest
  • Signs of high blood pressure including headaches, nosebleeds and pounding in your ears
  • Trouble catching your breath or feeling short of breath
  • Difficulty sleeping
  • Sudden changes in your mood

You may experience one or more of the following common side effects when taking phentermine:

  • Feeling itchy
  • Stomach pains
  • Dry mouth
  • Constipation
  • Frequent dizziness
  • Changes to your sex drive
  • Bad taste in your mouth

This is not a full list of side effects, and you may experience others that are not included above.

Speak to your doctor to understand more about the side effects you may experience when taking phentermine.

The link between phentermine and addiction

Woman crying on a bench

Is it possible to become addicted to phentermine?

As phentermine causes your brain to release large amounts of dopamine and serotonin, it’s possible to become addicted to this pleasurable sensation.

This is more likely to occur if you have a family history of addiction or use phentermine in a way that is not intended, such as snorting or injecting it.

Even if you use phentermine exactly as intended, you can still become addicted.

You may also find that your experience withdrawal symptoms when you stop taking phentermine, which is a sign that your brain and/or body has become dependent on this drug. [3]

You should never stop taking phentermine without your doctor’s knowledge.

If you use phentermine recreationally, without approval from a medical professional, your chances of developing an addiction are much higher.

This is because you are more likely to use higher amounts of this medication more frequently, as well as using it on a long-term basis which is not recommended.

What are the signs and symptoms of a phentermine addiction?

Using phentermine puts you at risk of developing an addiction, particularly if you are using this medication recreationally.

If you are using phentermine that has been prescribed to you by a medical professional, you may not realise that you have become addicted to this drug until you attempt to stop using it.

If you are using phentermine recreationally, addiction can sneak up on you without your knowledge.

However, there are several signs of a phentermine addiction that you can look out for in yourself or anyone you know that is using phentermine.

The below list is not exhaustive and there may be other signs of phentermine addictions that are not included in this article.

Common signs and symptoms of a phentermine addiction include:

  • Intense cravings for phentermine
  • Experiencing withdrawal symptoms when not using phentermine
  • Spending a lot of time thinking about, obtaining and using phentermine
  • Frequent nausea, with or without vomiting
  • Gastrointestinal issues including diarrhoea or constipation
  • Heart palpitations
  • Sweating profusely
  • Withdrawing from friends and family
  • Poor performance at work or school

If you believe that you may have a phentermine addiction, speak to your doctor straight away or call the OK Rehab team on 0800 326 5559.

Can I get phentermine in the UK?

Phentermine has not been approved for NHS use, which means it is extremely unlikely that your doctor will prescribe this medication to you.

Some private slimming clinics may prescribe phentermine to you, but it is recommended that you look into safer alternatives due to the potential dangers and addictive properties of this drug.

How long does phentermine stay in your system?

A woman practicing yoga

How is phentermine tested?

There are several ways to test for phentermine in your system including your urine, blood, hair and saliva.

Some workplaces run regular drug tests that may flag up phentermine, or your doctor may need to screen you in order to safely prescribe an additional medication.

Studies have shown that phentermine has a half-life of between 19-24 hours. Your body can metabolise 50% of this medication within this time, which means that it can take 5-6 days for phentermine to completely clear from your system and stop showing up in drug tests.

However, the effects of this medication are much shorter and should remain for just 4-12 hours.

This can change depending on how you ingest phentermine, and these figures are based on someone taking the drug orally.

If you inject or snort phentermine, it may remain in your system for a longer amount of time. Results may also vary depending on your weight and body fat percentage.

How long does phentermine stay in your urine?

A common way to test for phentermine in your system is to take a urine sample and test it.

You will need to thoroughly wash your hands and collect a sample of your urine in a clean and sterile container.

A urine sample can usually be taken at any time of day, but you may be specifically asked for a first-morning sample.

Phentermine usually remains in your urine for 48-72 hours, but in some cases, it may stay in your system for several days.

How long does phentermine stay in your blood?

Another way to test for phentermine is through a blood test, which will be performed by a medical professional.

You may be asked to refrain from eating for 24 hours before your blood test, although in many cases you will be able to eat normally.

The blood sample will be taken from a blood vessel in your arm, usually on the inside of the elbow.

You may feel a small scratching sensation, but the test should not be particularly painful and will only take a couple of minutes.

Phentermine can usually be detected in your blood for up to 24 hours, although in some cases this can be longer.

How long does phentermine stay in your hair?

Your hair follicles can provide a lot of information about you, including the medications that you have been using.

While other tests can detect phentermine for several days after you have used it, hair follicle tests can show if you have used phentermine in the past 90 days.

It is a simple procedure in which 100-200 strands of hair will be snipped from your head and taken away for testing. In some cases, you may be able to cut the hair yourself.

If you are bald or do not have enough hair, samples of your body hair may be used instead.

The test will not usually be affected if you have recently washed or dyed your hair, or use styling products.

How long does phentermine stay in your saliva?

Many people are not aware that your saliva can show whether you have used phentermine within the last few days.

A saliva test involves taking a swab from your mouth to obtain your saliva, which can then be tested for phentermine.

Your cheek will be swabbed with a small sponge on the end of a stick, making it a painless and non-invasive method of testing.

The only preparation you will need to undertake is refraining from eating or drinking 10 minutes before your test.

Phentermine can usually be detected in your saliva for 24 to 48 hours after your last dosage.

What are the risks of phentermine?

Taking phentermine while pregnant or breastfeeding

While the potential risks of taking phentermine while pregnant or breastfeeding have not been extensively studied, it is not recommended that you use this substance under these conditions.

There is no reason to take phentermine while pregnant, as it is commonly used as a weight-loss aid. In the vast majority of cases, it is not considered necessary to attempt to lose weight while pregnant, particularly with the use of pharmaceutical drugs.

Phentermine has been found to be excreted through breast milk, so it is not recommended that you take this medication until your baby is fully weaned.

If you are already taking phentermine when you discover that you are pregnant, you should speak to your doctor about stopping your dosage as soon as possible.

As phentermine is addictive, it may be difficult and potentially dangerous to stop taking it without professional help. It is possible to become addicted to phentermine even if you are taking it as directed.

Is it possible to overdose on phentermine?

Some people believe that phentermine is completely safe to use when prescribed by a doctor, but in reality, this medication can be extremely dangerous.

If you take too much of a certain substance, this is known as an overdose.

It is possible to overdose on phentermine, and the results could potentially be fatal. If you believe that your dosage is not producing the required effect, speak to your doctor instead of raising the dosage yourself.

An overdose may also be caused by combining phentermine with other substances such as alcohol or drugs. You should never smoke, consume caffeine, drink alcohol or ingest other medications when taking phentermine.

If you take too much phentermine, you are at risk of overstimulating your central nervous system. This could lead to raised blood pressure and heart failure.

Common symptoms of a phentermine overdose include:

  • Chest pain
  • Hallucinations
  • Involuntary tremors
  • Nausea
  • Abdominal cramps
  • Irregular heart rate

If you think that you or someone you know has overdosed on phentermine, call 999 straight away and seek immediate medical attention.


[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3928674/

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2687747/

[3] https://www.researchgate.net/publication/44889420_A_Study_of_Abrupt_Phentermine_Cessation_in_Patients_in_a_Weight_Management_Program