Although hair loss is not officially listed as a phentermine side effects, around 9% percent of users report phentermine hair loss while taking this medication (
Does Phentermine Cause Hair Loss?
Hair loss is not an official side effect of phentermine, but many patients notice a link between phentermine use and hair thinning or falling out in clumps. So, why does phentermine make your hair fall out?
Phentermine-related hormonal changes and weight loss could be to blame, but loss or thinning of hair may result from taking certain medications or indicate an underlying medical condition.
Why Phentermine Causes Hair Loss
Since phentermine hair loss is not a listed side effect of the medication, it is hard to determine what exactly is responsible for this relatively-common complication. However, the potency of the medication, rapid weight loss, nutritional deficiencies or underlying medical problems could help explain why phentermine is causing hair loss.
Here are four possible reasons why phentermine causes hair loss:
1. The Medication Itself
While many people associate chemotherapy drugs with hair loss, you may be surprised to learn that many other medications also cause hair loss related to chemical toxicity that affects hair follicle growth and development.
The follicle passes through three phases during its life cycle: anagen, catagen and telogen. These loosely correlate to the hair follicle’s phases of growth, death and falling out, respectively. Medications most often interrupt the growth of hair follicles, which leads to premature termination of anagen and early transition into telogen: the falling-out phase. This disruption, called telogen effluvium (TE), leads to hair thinning or loss (
The scalp is most heavily-affected by TE because 80-90% of the hair follicles in that area are in anagen (the growth phase) at any given time, which makes them more susceptible to damage (
Talk to your prescribing physician if you think phentermine is causing hair loss.
2. Nutritional Deficiencies
Nutritional deficiencies are another common cause of hair loss. Restrictive diets that eliminate entire food groups or slash protein intake put patients at increased risk for nutrition-related hair loss (
Like the medication itself, protein or other nutrient deficiencies can also cause hair loss or thinning in the form of telogen effluvium.
3. Rapid Weight Loss
Losing a lot of weight very quickly can also precipitate phentermine hair loss.
Phentermine is famous for producing impressive weight loss results in a matter of months, but slimming down too quickly can cause (or worsen) hair loss (
4. Underlying Medical Conditions
Last, but certainly not least, an undiagnosed medical condition could be responsible for hair loss on phentermine. Some common medical conditions in phentermine patients that may contribute to hair loss include hypothyroidism, PCOS and androgenetic alopecia (genetic baldness).
If weight loss and maintenance has always been difficult for you, ask your doctor about a thyroid function test. Hypothyroidism, or low/underactive thyroid, can cause thinning hair, weight gain, fatigue, constipation and depression, among other symptoms (
Polycystic ovary syndrome (PCOS) is another potential cause of weight gain and hair loss due to hormonal imbalances. Many women with PCOS find phentermine helpful to jumpstart adoption of healthy habits that promote weight loss. Decreasing excess weight, in turn, helps ease symptoms of PCOS and restore hormonal balance. However, if you suspect PCOS may be causing or contributing to your phentermine hair loss, bring it up to your gynecologist.
Drug-related hair loss, such as phentermine hair loss, can also trigger or worsen androgenetic alopecia,also known as genetic baldness (
Does Hair Grow Back After Phentermine?
Yes, hair usually grows back after taking phentermine but it takes time.
Most drug-related hair loss resolves on its own after the treatment finishes. If the damage is due to telogen effluvium (TE), hair regrowth after phentermine may not start for 2-6 months after finishing treatment (
While regrowth is typically perceivable by a doctor at 2-3 months, it may not be noticeable to you for up to 12-18 months (
Phentermine Hair Loss Treatment
Given the wide variety of potential causes for phentermine hair loss, there is no “one size fits all” phentermine hair loss treatment. Still, here are a few ideas to help prevent and treat hair this distressing side effect.
1. Lose Weight at a Healthy Rate
First and foremost, aim for a healthy rate of weight loss: around 1-2 pounds per week.
Losing weight too quickly not only increases lean muscle loss and probability of rebound weight gain, but also puts your hair at risk (
2. Focus on Nutrition
Some cases of phentermine hair loss can be prevented, or even treated, by eating a balanced diet with plenty of calories, protein, healthy fats and micronutrients.
Protein is necessary for hair growth and maintenance, so eating too little protein can cause hair loss (
8). Each day, consume at least 0.8 grams of protein per kilogram of body weight ( 9). Choose lean protein sources like grilled or baked turkey or chicken breast, lean beef, fish, low-fat/nonfat dairy, eggs, tofu or nuts to fulfill this need.
- Healthy Fats
A deficiency of unsaturated fatty acids (omega-6s and omega-3s) can cause or worsen hair loss. Oily fish (such as salmon), avocado and olive oil are all good sources of healthy, monounsaturated omega-3 fatty acids.
Several vitamins and minerals are also critical for hair growth and maintenance, which may help prevent phentermine hair loss. These include:
Also known as vitamin B7 or vitamin H, biotin is a common ingredient in ‘hair and nail’ supplements because too little of this nutrient can cause hair loss. However, it’s produced naturally by intestinal bacteria so deficiency is rare in healthy adults. Despite its mainstream popularity, there is little evidence to support biotin supplementation in the absence of clinical deficiency (
- Vitamin D
Low levels of vitamin D can contribute to hair loss (
10). Talk to your doctor if you suspect a vitamin D deficiency. Supplements, increased dietary intake and more time outdoors are all easy & effective treatments.
Iron is the most common nutritional deficiency in the world and, in the US, anemia affects an estimated 5.6% of the population (
10, 11). Unfortunately, low iron can contribute to hair loss ( 10). So eat plenty of lean beef, clams, oysters, enriched breakfast cereals, beans and tofu to minimize this risk factor for phentermine hair loss.
Consuming too little zinc can make hair brittle or fall out. Thankfully, this is a very rare problem in modern diets. Talk to your doctor if you are concerned about zinc deficiency. Do NOT take large amounts of extra (supplemental) zinc without a doctor’s order since too much zinc is toxic (
3. Consult a Professional
Talk to your doctor if your phentermine hair loss becomes noticeable or distressing.
He or she can run tests and help you determine exactly why your hair is thinning or falling out. It may be phentermine and the associated weight loss/dietary changes, but it could also be another medical issue or medication. A medical professional is the best person to assess why your hair health has deteriorated.
4. Stop Taking Phentermine
After examining you and running some tests, your doctor may determine that phentermine is causing hair loss. If the medication is the root of the problem, he or she may recommend that you stop taking it.
Always follow your doctor and pharmacist’s instructions precisely regarding phentermine dosage and, if applicable, stopping phentermine.
- Members of “Losing Weight with Phentermine” Support Group on Facebook & Phentermine.com Forum. (2019, March 13). [User Report of Common Phentermine Side Effects]. Unpublished raw data.
- Patel, S., & Tosti, A. (2014). An overview of management of drug-induced hair and nail disorders. Clinical Practice, 11(3), 327-339. doi:10.2217/cpr.14.18
- American Osteopathic College of Dermatology. (n.d.). Telogen Effluvium Hair Loss.
- Redfearn, S. (2015, December 16). Hidden Causes of Hair Loss (D. Jaliman MD, Ed.).
- Mayo Clinic Staff. (2018, December 04). Hypothyroidism (underactive thyroid).
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- Guo, E. L., & Katta, R. (2017). Diet and hair loss: Effects of nutrient deficiency and supplement use. Dermatology Practical & Conceptual, 7(1), 1-10. doi:10.5826/dpc.0701a01
- Le, C. H. (2016). The Prevalence of Anemia and Moderate-Severe Anemia in the US Population (NHANES 2003-2012). Plos One, 11(11). doi:10.1371/journal.pone.0166635