Key Takeaway
Phentermine, a prescription medication for weight loss, typically stays in the system for about 1 to 4 days.
Specific factors, such as the pH of urine, could also alter how long phentermine stays in your system, as could combining phentermine with other drugs. Specifically, acetazolamide, could reduce the time phentermine can be detected in your system [1].
What Is Phentermine?
Phentermine is a prescription drug that belongs to a class of medications known as anorectics, meaning it suppresses appetite and promotes weight loss [2]. This means it is used for similar purposes as semaglutide, pemvidutide, dulaglutide and tesofensine, although the way it works is different.
It was first discovered in the 1960s and has been approved for the treatment of obesity together with topiramate since 2012. It should primarily be used in overweight or obese individuals with one or more obesity-related conditions, such as hypertension, high blood pressure, or musculoskeletal difficulties [3].
How Long Does Phentermine Stay In Your System?
Phentermine can stay in your system, as detected by urine sample, for one to four days post drug administration. This will depend on multiple factors, including your health condition, herbal products, such as ashwagandha, you may be taking, and whether you exercise regularly.
A prominent literature source looked at the excretion rates of doping agents, including phentermine hydrochloride also known as phentermine [4]. This study found that the most phentermine was excreted 4 hours after taking it, with up to 85% of it being excreted after 72 hours.
How long phentermine stays in your system can be reduced by taking it in a sustained release capsules, called Ionamine 15. Specific factors, such as the pH of urine, could also alter how long phentermine stays in your system, as could combining phentermine with other drugs. Specifically, acetazolamide could reduce the time phentermine can be detected in your system [1]. It's important to note that the effects of the drug may wear off sooner, even though traces of the medication can still be detected in the body.
Factors influencing how long phentermine stays in your system
The duration that phentermine stays in your system can also be influenced by factors such as the dosage taken, the individual's metabolic rate, and the specific formulation of the drug. For instance, a sustained-release formulation of phentermine may have a longer excretion rate .
How Is Phentermine Excreted From Your System?
Phentermine is primarily excreted from your system through urine, so factors such as hydration and urine pH influence how long phentermine stays in your system.
How Long Should You Use Phentermine For?
Phentermine is a medication that should be used for short periods to aid in weight loss, in combination with exercise and diet regulation. The duration of treatment depends on how you respond to the medication, but most people take phentermine for 3 to 6 weeks [5].
Short-term use is recommended to avoid potential side effects, such as dependence on the medication and serious side effects, like personality changes and psychosis [3]. These side effects have been noted in patients with Parkinson’s Disease that have been treated with levodopa, a form of dopamine, for extended periods of time. Although the levodopa reduced dyskinesia and akinesia, it increases the risk of mania and psychosis. The risk of developing mania and hyperkinetic movements in phentermine is significantly lower since it only enhances endogenous dopamine release.
The length of time you take phentermine will be individual and must be discussed with your healthcare provider. In the literature, the longest duration of phentermine medication was up to three years in a treatment centre. However, this study also included patients who only completed one year of phentermine treatment, with few making it to three years. Critically, the discontinuation of phentermine was not due to side effects but rather to the patient’s choice to end the treatment at the weight loss clinic [6].
If you are taking phentermine for performance-enhancing purposes, make sure to inform your healthcare provider still and only take it for up to 6 months. Exceeding this duration without medical supervision significantly increases the risks of side effects, which outweigh potential short-term performance enhancement [1].