How long does Adipex stay in your system? (3+ factors)

In this article, we will answer the question, ” How long does Adipex stay in your system?” we will also discuss some factors which can affect the elimination of the drug. Additionally, we will talk about the toxicity of Adipex if it stays in your system for too long. 

How long does Adipex stay in your system? 

Adipex stays in the system for about 2-4 days before it is completely eliminated from the body. The half-life of Adipex is 20 hours, which is the time needed for the drug to reduce itself by 50%. (1,2)

The elimination process of Adipex is carried out more rapidly if the urine is acidic. 80% of Adipex is eliminated through urine in an unchanged form. Acidic urine makes Adipex more soluble in the urine and enhances its degradation, which eliminates the drug more rapidly. (1)

The time taken by the drug to get eliminated from the body varies among individuals, and factors such as metabolism, dose, and individual differences influence the elimination of the drug. 

How is Adipex eliminated from your body? 

Adipex (Phentermine) has a similar mechanism as amphetamine, which acts as an agonist at the TAAR1 receptor site and stimulates the release of norepinephrine and epinephrine. Adipex is used as a short-term adjuvant treatment for weight reduction along with exercise, behavioural modification and caloric restriction. (2)

Phentermine is metabolised by hydroxylation and oxidation by the CYP3A4 enzyme. Adipex is excreted through urine in an unchanged form. About 70% to 80% of the drug is excreted via urine. The elimination of Adipex is more rapid if the urine is acidic. (1,2)

Hepatic or renal dysfunction can concomitant use of certain drugs can decrease the elimination of the drug from the body, which can cause a build-up of Adipex in the body, leading to toxicity. 

What are the factors affecting the elimination of Adipex? 

There are a few factors which can affect the elimination process of Adipex from your body, such as: 

  • Metabolism: The rate of metabolism differs from person to person. If the metabolism is slow, the drug may take longer to get eliminated. 
  • Dose: The higher the dose of Adipex, the higher the elimination rate. 
  • Frequency: The higher the frequency of Adipex, the longer it stays in your urine and the longer the elimination time. 
  • Hydration: A dehydrated body will reduce the removal of drugs from the body. 
  • Pre-existing condition: Liver and kidney dysfunction can affect the metabolism and elimination of the drug. If the organs don’t work properly, the drug stays in the system longer.
  • Concomitant use of medication: Use of Adipex with other medications, such as antidepressants, sodium bicarbonate, etc., can influence the elimination of the drug. 

How much Adipex in your body can cause toxicity? 

The dose of Adipex varies depending on certain conditions and individual responses. The usual adult dose of Adipex is 37.5mg daily, taken before breakfast on an empty stomach or 1-2 hours after breakfast. 

The blood concentration of Adipex ranges from 0.5-250 µg/mL. An increase in this concentration can cause toxicity in some individuals. The clinical features reported with Adipex toxicity and side effects are as follows: (2)

Toxicity symptoms Side effects
  • Drowsiness
  • Vertigo
  • Agitation
  • Mydriasis
  • Seizures
  • Somnolence
  • Bradykinesia
  • Tachycardia
  • Fever
  • Dry mouth
  • Headache
  • Constipation
  • Paresthesia
  • Increased heart rate
  • Valvular heart disease
  • Psychiatric and cognitive dysfunction 
  • Insomnia
  • Hypoglycemia

How to ensure safe and effective use of Adipex? 

You can ensure safe and effective use of Adipex by following a few simple steps such as: 

  • Take Adipex as prescribed by your healthcare provider. 
  • Drink plenty of water while taking the medication. 
  • Make sure you follow a good diet and exercise.
  • Monitor for any side effects while taking Adipex.
  • Avoid abrupt discontinuation of the drug, as it can cause withdrawal symptoms.
  • Keep a record of your weights while you are taking Adipex to monitor your progress. 
  • Avoid drinking alcohol while consuming Adipex.

Who should avoid Adipex? 

Adipex should be used only under the guidance of a qualified physician to avoid any harm. The dose of Adipex is modified based on the individual’s specific condition; there are certain conditions where Adipex should be avoided, such as: (2)

  • Pregnancy 
  • Breastfeeding
  • History of cardiovascular disease
  • High blood pressure
  • Hyperthyroidism
  • History of drug abuse 
  • Glaucoma
  • Psychiatric illnesses such as anxiety and depression.

As per my knowledge, Adipex can stay in your system for about 48-72 hours. However, the elimination of the drug can be influenced by some factors and can increase the elimination time of the drug. Hence, it is important to consult a physician, who will evaluate for any underlying condition that may affect the elimination of Adipex and help minimise the toxicity of the drug. 

Was this helpful?

Thanks for your feedback!



PubChem [Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information; 2004-. PubChem Compound Summary for CID 4771, Phentermine; [cited 2023 Aug. 21]. Available from: 


Johnson DB, Quick J. Topiramate and Phentermine. [Updated 2023 Mar 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: