Phentermine can cause temporary hair loss, most commonly through telogen effluvium triggered by rapid weight loss, caloric and nutrient deficiency, metabolic and hormonal stress, or thyroid disruption, and although it may also “unmask” underlying androgenetic alopecia, the shedding is generally reversible with adequate nutrition, stress management, and medical evaluation.
People taking phentermine can experience some hair loss, but the good news is that it’s not permanent. In this guide, we’ll explain why taking phentermine can result in hair loss and what steps you can take to reverse it and regrow your hair.
What is phentermine?
Phentermine (Brand name in the US, Lomaira) is a medicine known as an anorexiant, a stimulant of the central nervous system known to suppress appetite and cause weight loss. It is used for short term treatment of weight management.
Does phentermine cause hair loss?
The most serious side effects of phentermine include cardiovascular (blood pressure and heart rate) abnormalities, central nervous system (psychosis, insomnia, anxiety) and pulmonary hypertension, a serious condition affecting the lungs and the heart, leading to heart failure.
As a less serious adverse effect, hair loss can happen when taking phentermine because the medication is designed to suppress appetite, and this can result in nutritional and mineral deficiencies as well as a stress response in the body. (1) The rapid weight loss that can occur in some patients taking phentermine can cause an acute reactive process known as telogen effluvium. This phenomenon is true for people who experience rapid weight loss from whatever the cause, whether it's from taking medication or other reasons such as childbirth or illness. (2)
Can phentermine trigger telogen effluvium?
Telogen effluvium (TE) is the most common reason patients experience hair loss while taking phentermine. TE happens to many people because of the caloric reduction and nutrient depletion as well as hormonal changes that can occur when their weight drops rapidly. These stressors can put hair follicles into telogen phase which is where the hair sheds. This is because phentermine reduces the patient’s appetite enough that their body cannot adapt to the changes caused by eating less.
Rapid weight loss and hair shedding
Losing more than 1 – 2 pounds per week can cause protein and micronutrient deficiency, elevated cortisol levels, shifts in thyroid function, and can disrupt normal hair cycles. This is true for any cause of rapid weight loss and is not exclusive to patients taking phentermine. (3)
Calorie restriction and nutritional deficiencies
Phentermine can often be a game changer for weight loss, but its effectiveness comes with risks. Undereating can be problematic, and even though the positive outcome is lower body fat, the fuel that comes with normal eating cycles is lowered as well. Talk to your doctor if you’re taking phentermine and you’re concerned about any hair shedding to rule out any other possible causes. (4)
Protein intake and hair growth (and key vitamin/mineral deficiencies)
Hair is mostly made of the protein keratin and if the amount of protein being ingested drops dramatically, then the available protein in the body is allocated to other more important areas such as essential organs. This is why hair may shift into the telogen phase and starts to shed. By dropping your caloric intake rapidly, you change the amount of iron, B12, biotin, folate, zinc, and essential fatty acids your body needs to grow strong, healthy hair. (5)
There needs to be a balance achieved where your diet changes, and it is important to keep these key nutrients and protein at appropriate levels of intake to support your hair health.
Stress, cortisol and metabolic strain
Phentermine is a central nervous system stimulant, so it can increase a patient’s heart rate, cortisol levels, and overall alertness. The “physiologic stress” of rapid or significant weight loss can accelerate hair shedding, and anyone experiencing chronic elevated cortisol levels should speak with their doctor before they take phentermine. Metabolic stressors are often associated with telogen effluvium regardless of the cause.
Hormonal shifts during weight loss
Rapid weight loss has a direct influence on hormones, including those associated with hair growth. Estrogen, testosterone, thyroid hormones, cortisol, and insulin are all affected by changes in body weight. The hair follicle is a structure known as a paracrine organ, which requires and enables signaling from cell to cell in order for hair to cycle and grow normally. These signals to the hair follicle come from stimuli including various hormonal and metabolic factors all acting in a coordinated manner to bath the hair follicle in the right “mix” allowing hair to grow and shed normally. When this is disrupted as might happen with rapid weight loss, this normal growth/shedding process is impacted negatively with more shedding as a consequence. (6)
Thyroid and hair shedding during medication-assisted weight loss
Taking phentermine can alter a patient’s thyroid function, especially for those who are genetically predisposed to it and have a family history of thyroid issues. Hypothyroidism (low thyroid function) as well as hyperthyroidism (elevated thyroid function) can cause mood changes, sleepiness, and hair shedding. (7)
It’s best to get your thyroid tested before taking phentermine to determine whether this medication causes any negative impact on thyroid function.
Phentermine vs phentermine–topiramate and hair loss
Phentermine-topiramate which goes by the brand name Qsymia can be more likely to result in hair loss than taking phentermine alone. This is because phentermine-topiramate is a combination of 2 drugs that can cause weight loss, phentermine and topiramate. (8) Topiramate is sold under the brand name Topamax and is another drug used to help with weight loss, but is also used for treating epilepsy, seizures, and migraines. Qsymia and Topamax are FDA approved, with Qsymia being the FDA approved specifically for weight loss. The combination is even more effective for weight loss, and as a result, it comes with an increased risk of side effects such as hair loss. (9)
Does taking phentermine cause severe hair loss?
It’s not common to experience severe hair loss when taking phentermine, but it can happen. If your weight loss is quite significant, then your caloric deficiency and nutritional deficiencies would be as well. If you start noticing bald spots and handfuls of hair, then contact your doctor right away to ensure you’re not doing more harm than good.
Why phentermine may “unmask” genetic hair loss
Many men first experience male pattern hair loss (androgenetic alopecia, or AGA) during rapid weight loss as recession may become more noticeable with less subcutaneous facial fat.
With AGA, even after the patient resumes a normal diet and gains weight, their hair loss will remain and in fact will progress.
Since there is no known interaction between phentermine and finasteride (10), anyone who sees hair loss while taking phentermine to lose weight can start addressing their AGA, or DHT related hair loss, at the same time with medications such as finasteride or minoxidil.
Male pattern hair loss becoming noticeable during dieting
If you suspect your hair is shedding while taking phentermine it is quite possible that your hair loss is related to AGA (due to DHT sensitivity) and unrelated to weight loss associated with the medication you are taking. It is advisable to see a doctor if you notice hair loss, even if on a medication. You may have inadvertently helped yourself by bringing your AGA to your attention, which is a good thing if you want to stop it. (11) The earlier you start treating androgenic alopecia with medication such as topical finasteride, the better your chances are of stopping the hair loss.
How long phentermine-related shedding lasts
Telogen effluvium, a reaction related to rapid weight loss which can be caused by taking phentermine, normally starts within 2 – 6 months of starting the medication at which point you should expect another 6 – 12 months of hair shedding before recovering. The time it takes to recover will depend on how you adjust nutrition levels. (12) What you eat while eating less is what can cause hair loss so planning ahead of time with a nutritionist is advisable. Being proactive and speaking to your doctor beforehand can help avoid any hair loss so don’t be shy to bring up these concerns when you first get phentermine prescribed.
How to reduce hair loss while on phentermine
By being proactive with your health when taking medications like phentermine that can have a significant impact on your body, you can reduce the possibility or severity of any hair loss. Avoiding an extreme caloric deficit by replacing those lost calories from your normal diet with other foods is advisable. Stick to a solid diet plan. Foods such as fish, eggs, lean meats, leafy greens, and nuts are all ideal. Taking supplements like iron, B12, vitamin D, zinc, omega 3s, and adding protein powders or shakes to your daily routine can help with your calories and assist with your new eating habits too. (13)
In addition to your nutrition, ensure you get a proper night's sleep every night to keep your cortisol levels healthy. Phentermine is a stimulant, so talk to your doctor if it's having an impact on your sleeping habits.
When to seek medical evaluation
If your hair loss continues after 6 months or you notice that it’s more than shedding and you have bald patches or significant hairline recession, then talk to your doctor to rule out any other underlying conditions such as androgenetic alopecia. Telogen effluvium could indicate an adverse reaction to the medication, so talk to your doctor right away if you notice that you're experiencing more than a bit of hair shedding.
What to do next / recommended treatment pathways
Picking the best path forward will depend on what is causing your hair loss. If you have been clinically evaluated and know it’s telogen effluvium and temporary, then focus on your diet by increasing your caloric intake with high protein foods, supplements, and protein shakes. Combining diet changes with a focus on stress reduction, good sleep hygiene and abstaining from other stimulants like caffeine or other drugs, are your best chance at regrowing your hair quickly.
If you’ve found that your hair loss is likely genetic then these adjustments won’t necessarily help that much. For any hair loss you uncover that is caused by androgenic alopecia, you’ll need to try something like finasteride and/or minoxidil. A dermatologist can help direct you on which medication is best for your hair loss, and if you’re worried about the side effects from taking finasteride in its pill form then topical finasteride may be a great option. Topical finasteride with minoxidil in XYON’s SiloxysSystemTM gel technology, has the benefits of limiting systemic absorption.
There are benefits to taking phentermine for weight loss and the hair loss risk associated can generally be minimized with proper planning and discussions with your doctor.
References:
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Telogen effluvium associated with weight loss: A single-center retrospective study. Annals of Dermatology, 36(2).
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Diet and hair loss: effects of nutrient deficiency and supplement use. Dermatology Practical & Conceptual, 7(1), 1–10.
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https://pubmed.ncbi.nlm.nih.gov/28243487/
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https://doi.org/10.3390/biomedicines12030513
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SingleCare Editorial Team. (2024).
Qsymia vs. phentermine: What’s the difference? SingleCare.
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Bashir, S., & Dar, M. (2024).
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Gupta, A. K., Venkataraman, M., Talukder, M., Bamimore, M. A. (2022).
Finasteride for hair loss: A review. Journal of Dermatological Treatment, 33(4), 1959506.
https://doi.org/10.1080/09546634.2021.1959506
https://pubmed.ncbi.nlm.nih.gov/34291720/
Ntshingila, S., Oputu, O., Arowolo, A. T., & Khumalo, N. P. (2023).
Androgenetic alopecia: An update. Journal of Dermatology & Dermatologic Surgery, 27(3). https://doi.org/10.1016/j.jdds.2023.07.005
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PMCID: PMC4606321
