Phentermine side effects in females: what to know as a woman

Phentermine is a popular prescription weight loss drug — more than 2 million prescriptions were written in 2021 alone. But, if you’re a woman who’s considering taking it, you may be wondering about phentermine side effects in females. 

In this article, we cover everything you need to know about how taking phentermine can affect you as a woman. Learn about what it does in the body, its side effects in women, how it affects female hormones, and how it compares to similar medications.

Wondering how to get weight loss medication, like phentermine, online? A telehealth provider on Klarity Health can evaluate your weight loss needs and create a treatment plan that may include medication. Get started when you find a provider on Klarity Health today.

What does phentermine do in the body?

Phentermine belongs to a class of medications known as anorectics, or appetite suppressants. It’s also a central nervous system (CNS) stimulant, specifically an amphetamine substitute. It works by increasing the levels of 3 brain chemicals that help transmit signals throughout your nervous system — serotonin, noradrenaline, and dopamine. Increasing these chemicals is thought to stimulate satiety (feeling full after eating), improve metabolism, and help break down stored fat. Overall, the result is weight loss. 

But, CNS stimulants, like amphetamines and amphetamine substitutes, are known to affect female hormones — specifically progesterone and estradiol. These hormones prevent pregnancy and control menstrual bleeding, respectively. They’re also the active ingredients in most oral contraceptives. 

Research shows amphetamines increase estrogen and decrease progesterone. And, this can have adverse effects in females who take these or similar stimulant medications, such as phentermine.

What are phentermine’s side effects for women?

Phentermine can cause side effects regardless of your sex. But, they may be worse or different if you’re a woman.  

Common phentermine side effects for women

People taking phentermine report some common side effects, like palpitations, restlessness, insomnia, and headache. The following are potential side effects for phentermine: 

• Constipation
• Diarrhea
• Dizziness
• Dry mouth
• Headache
• Increased blood pressure
• Increased heart rate
• Itchy skin or hives
• Restlessness
• Sexual side effects
• Tremor
• Trouble sleeping
• Unpleasant (or metallic) taste in the mouth

Some of these side effects affect men and women differently. For example, phentermine’s sexual side effects differ between women and men. Men may experience impotence and/or erectile dysfunction. But, if you’re a woman taking phentermine, you may experience difficulty becoming aroused, delayed orgasm, and/or pain during intercourse. 

Potentially serious phentermine side effects for women

Serious side effects are rare and occur in fewer than 0.1% of people. Serious side effects of phentermine include:

• Pulmonary hypertension (high blood pressure in the blood vessels of the lungs)
• Valvular heart disease
• Impaired functioning (for example, operating machinery or driving a car)
• Developing tolerance to the medication/potential for withdrawal symptoms

It’s unclear if the serious side effects of phentermine differ between men and women. If you experience any serious side effects with phentermine use, get medical care immediately.

What women need to know about taking phentermine

If you’re a woman taking phentermine, here are some important things to know.

Does phentermine affect your period?

Phentermine isn’t known to directly affect hormone levels. But, you may experience fluctuations in your menstrual cycle if you lose a significant amount of weight while taking it. You may not notice these effects if you also take birth control or hormone replacement therapy. 

If you experience significant or adverse changes in your period while taking phentermine, talk to your weight loss provider or obstetrician/gynecologist (OB/GYN). 

Can you take phentermine and birth control?

You can take phentermine while you’re on a birth control pill, though there isn’t a lot of research on the combination. You should be aware that phentermine may decrease the effectiveness of birth control pills. You may also experience irregular spotting or breakthrough bleeding while taking it. Talk to your healthcare provider about whether it’s safe to take phentermine with oral birth control and how it could affect you.

Can you take phentermine while pregnant?

No, taking phentermine while pregnant isn’t recommended. Pregnant women are expected to gain a certain amount of weight, even if they’re obese. It isn’t recommended to take phentermine and lose weight, and it may cause fetal harm. There isn’t much research due to potential risks to pregnant women.

If you become pregnant or are planning to while taking phentermine, talk to your healthcare provider. It’s recommended that you stop taking it before you try to get pregnant. Your provider will help you stop taking phentermine safely.

Can you take phentermine while breastfeeding?

It isn’t known if phentermine is transferred through breast milk, but other amphetamines are. Because of this, you shouldn’t take phentermine while breastfeeding. 

Typically, women lose weight while breastfeeding postpartum. If you still need help losing weight during this time, talk to a healthcare provider about safer options. 

Does phentermine affect menopause?

During menopause, hormonal changes lead to an increase in stored fat. The resulting weight gain can negatively impact your health, but phentermine may help combat this. Because phentermine doesn’t directly affect hormone levels, it doesn’t likely affect menopause. In fact, your provider may recommend it to help you lose weight gained during menopause. 

If you’ve gained weight during or after menopause, talk to your healthcare provider about whether phentermine or another weight loss program or medication is appropriate. It may not be safe for you if you have heart problems. 

Are there long-term phentermine side effects in females?

Phentermine is only approved by the U.S. Food and Drug Administration (FDA) for short-term use (up to 3 months). But, ongoing studies show that phentermine is safe for long-term use and can lead to even greater weight loss. Your healthcare provider can prescribe it for longer than 3 months if it’s safe and effective for you, but this is an off-label use (use for something it’s not FDA-approved for). 

If you use phentermine long-term, you may experience personality changes or psychosis. Get medical care immediately if this happens. 

How do phentermine’s side effects compare to other weight loss meds?

You’ll likely experience fewer side effects with phentermine than with other weight loss medications. 

Side effects of phentermine compared to Qsymia and Wegovy

Compare common and serious side effects among prescription weight loss pills, phentermine and Qsymia (phentermine-topiramate), and weight loss injection Wegovy (semaglutide) below.

Learn more about phentermine vs Wegovy and Wegovy side effects.

Key takeaway

• Phentermine is a popular solution for medically-supervised weight loss. It works by stimulating the CNS to suppress appetite, boost metabolism, and reduce stored fat. But,  it and similar CNS stimulants have side effects that affect women specifically.
• Like any medication, phentermine can cause common and serious side effects. They’re largely the same for men and women.
• Phentermine’s sexual side effects differ between men and women. And, there are additional warnings if you’re a woman taking phentermine as part of a medical weight loss program. These have to do with periods, pregnancy, breastfeeding, and menopause. Consult a healthcare provider to make sure phentermine is safe for your specific situation. 
• Because phentermine has fewer side effects than other weight loss drugs, it may be a preferred option for you — if your provider thinks it’s safe for you.

A weight loss medication consultation is a click away

Ready to start your weight loss journey, but not sure how? It’s easy when you consult a provider on Klarity Health. During your consultation, your provider will evaluate your weight loss needs and create a treatment plan that may include medication. Get started and find a provider today. 

Sources

Agency for Healthcare Research and Quality (AHRQ), Medical Expenditure Panel Survey (MEPS) 2013-2021, obtained from ClinCalc DrugStats Database version 2024.01, updated Jan. 2024, https://clincalc.com/DrugStats/Drugs/Phentermine

Biomedicines, Amphetamine-Decreased Progesterone and Estradiol Release in Rat Granulosa Cells: The Regulatory Role of cAMP- and Ca2+-Mediated Signaling Pathways, Chung-Yu Chen et al., May 2021, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8145484/

DailyMed, Label: Phentermine hydrochloride tablet/phentermine hydrochloride capsule, https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=3b44d104-a7d0-4366-9d42-63f784f3cb22

DailyMed, Label: Qsymia- phentermine and topiramate capsule, extended release, https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=40dd5602-53da-45ac-bb4b-15789aba40f9

DailyMed, Label: Wegovy- semaglutide injection solution, https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b

Mayo Clinic, Phentermine (Oral Route), https://www.mayoclinic.org/drugs-supplements/phentermine-oral-route/side-effects/drg-20075169?p=1

North American Menopause Society, Changes in Weight and Fat Distribution, https://www.menopause.org/for-women/sexual-health-menopause-online/changes-at-midlife/changes-in-weight-and-fat-distribution

Obesity, Safety and Effectiveness of Longer-Term Phentermine Use: Clinical Outcomes from an Electronic Health Record Cohort, Kristina H. Lewis et al., Apr. 2019, https://pubmed.ncbi.nlm.nih.gov/30900410/

Pharmacology Biochemistry and Behavior, Differential subjective effects of D-amphetamine by gender, hormone levels, and menstrual cycle phase, Tara L. White et al., Nov. 2002, https://www.sciencedirect.com/science/article/abs/pii/S0091305702008183

StatPearls Publishing, Oral Contraceptive Pills, Danielle B. Cooper & Preeti Patel, updated Feb. 2024, https://www.ncbi.nlm.nih.gov/books/NBK430882/

The information provided in this article is for educational purposes only and should not be construed as medical advice. Always seek the guidance of a qualified healthcare professional with any questions or concerns you have regarding your health. Providers on Klarity Health are independent practitioners with full medical authority. No diagnosis result or treatment option is guaranteed for the services rendered through the Klarity Health platform.

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