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Common phentermine side effects in females

Phentermine side effects in females include menstrual cycle changes and lower sex drive
Kristi Torres writer headshot
By | Jun. 1, 2023
Doctor talking to female patient: Phentermine side effects in females

Key takeaways

  • Phentermine is a prescription medication used in conjunction with lifestyle changes for short-term weight loss. In females, it can cause menstrual irregularities and decreased libido in females.

  • Due to its amphetamine properties, phentermine has stimulant effects, potentially causing restlessness, insomnia, and increased heart rate. The medication is contraindicated in women with a history of heart problems.

  • While not directly linked to hair loss, significant weight loss from phentermine can influence hormonal fluctuations affecting the menstrual cycle and fertility.

  • Pregnant and breastfeeding women should not take phentermine due to potential harm to the fetus or infant. For women who are at high risk of heart disease or those experiencing adverse effects, providers should consider alternative treatments.

In this article:

 

Phentermine is a prescription weight loss medication used in the short-term treatment of obesity, along with lifestyle modifications and a reduced-calorie diet. Phentermine works in the central nervous system (CNS) to cause appetite suppression. As a stand-alone product, phentermine has been around for many years. 

Phentermine became popular in the 1990s, as it was once part of a popular weight loss therapy combination of fenfluramine and phentermine together. This was known as “fen-phen” to many back then. While the regimen was successful in aiding weight loss for many, fenfluramine specifically was later found to have fatal hypertension and heart valve effects. Fenfluramine was withdrawn from the market after billions of dollars in legal damages were awarded to survivors and victims’ families. Phentermine was not shown to have these effects and could remain on the market as a prescription appetite suppressant. Phentermine is a derivative of methamphetamine and, as such, remains a controlled substance in the U.S. market.

RELATED: Is phentermine for weight loss safe?

Obesity in women

Obesity is increasingly prevalent in the United States. One in three adults is considered “overweight,” with a body mass index (BMI) of 25 to 29.9. Unfortunately, even more are considered “obese” with a BMI over 30. Severely obese is defined as a BMI over 40, which is more likely to affect women than men. Women have also been shown to be more affected by some of the psychological effects of obesity, such as depression and low self-esteem. While phentermine and other weight loss drugs can cause potential side effects in both male and female users, there are important factors specific to females to consider with phentermine therapy. Women are more likely to develop severe obesity, and if beginning treatment, it’s important to be aware of the side effects phentermine may cause.

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What are common phentermine side effects in females?

Phentermine has common side effects known to occur in both men and women. These adverse events result from phentermine’s action in the central nervous system. Phentermine is a stimulant related to amphetamine drugs, and it can cause restlessness, dizziness, nausea, headaches, and tremors. 

Some patients may have difficulty sleeping (insomnia) while taking phentermine. Itching, dry mouth, and constipation have also been known to occur. 

Phentermine can cause symptoms such as overstimulation, euphoria, or dysphoria in some patients. In rare cases, it can lead to psychosis. Phentermine is only indicated for short-term use and should not be taken for long periods of time. 

Does phentermine cause hair loss?

Phentermine is not directly associated with hair loss, though weight loss, especially if it occurs quickly, can lead to hair loss (alopecia).

Does phentermine affect your period?

While phentermine does not directly affect hormone levels in the body, losing a significant amount of weight can cause a fluctuation in hormone levels. This can affect menstrual cycles, making them occur either more or less frequently than before. If taking birth control or hormone replacement therapy, this effect may be masked.

Does phentermine increase sex drive?

The indirect effect on hormone levels, coupled with CNS stimulation, can affect libido and sexual drive. With CNS stimulation, blood flow, and signal transmission are sometimes diverted away from the reproductive organs and genital areas to other parts of the body. In men, this can lead to impotence and erectile dysfunction, but the effects in women are different. Women tend to experience difficulty becoming aroused, delayed orgasm, or pain during intercourse.

Does phentermine raise blood pressure?

Heart disease is one of the most fatal disorders in women. Phentermine has been linked to cases of high blood pressure, pulmonary hypertension, and chest pain. Women who have a history of heart problems should not take phentermine, as it can cause irregular cardiac valve disease, palpitations, tachycardia (increased heart rate), and ischemic events. While phentermine is safe in patients with no known cardiac history, it should be avoided in those who have cardiac disorders or risk factors for cardiac disease. These risk factors may include high blood sugar, kidney problems, or a family history of cardiac disorders such as congestive heart failure and other heart-related medical conditions.

Phentermine and pregnancy

Phentermine is contraindicated in pregnancy. Weight loss offers no benefit to a pregnant woman, and it could potentially result in fetal harm. No weight loss is recommended for pregnant women, even those who are obese.

Phentermine can have an indirect effect on fertility, as overweight and obese patients who lose weight may be able to become pregnant more easily. Patients should use a contraceptive method to prevent pregnancy. If planning to become pregnant, stop taking phentermine before attempting to conceive.

Because phentermine is contraindicated in pregnancy, there are no controlled clinical trials to look at birth defects or spontaneous abortions due to phentermine. Retrospective analysis of first-trimester use of phentermine has shown no higher rate of miscarriage in women who took phentermine than women who did not, though these results are from a relatively small sample of women. The lack of clinical data makes determining if phentermine crosses the placenta difficult.

RELATED: What medications are safe to take during pregnancy?

Phentermine while breastfeeding

Phentermine is not well-studied in breastfeeding mothers due to safety concerns. Phentermine is contraindicated for breastfeeding mothers. The potential for serious adverse effects on an infant from phentermine exposure through breast milk makes it unsafe to study the effects. Typically, mothers who are breastfeeding experience weight loss postpartum. If additional help losing weight while still breastfeeding is needed, discuss options with a healthcare provider. Exercise and healthy food choices are the safest options while still breastfeeding. It takes approximately 3 to 5 days to eliminate phentermine from the body’s system, and this should be taken into consideration when breastfeeding.

RELATED: What a pharmacist wants you to know about breastfeeding and medications

Phentermine for menopause

Women who are postmenopausal are likely to experience persistent weight gain. One in five women will gain 10 pounds or more during the menopause transition. Increasing age and decreasing energy are linked to this weight gain. Still, menopause and the associated hormonal changes are specifically responsible for increased fat deposits in the abdominal region in postmenopausal women. Increasing weight can negatively affect a woman’s health, and clinicians may differ in how they approach the need for weight loss.

Healthcare providers may hesitate to recommend a weight loss medication to women of menopausal age due to possible other risks and adverse events. Women with pre-existing heart conditions should not take phentermine or other diet medications. However, untreated obesity can also have adverse cardiac health effects. A weight loss of just 5% to 10% of the current body weight can significantly benefit obese adults. A healthcare provider may suggest trying to achieve this with a diet and exercise weight loss plan before prescribing a weight loss drug like phentermine. Phentermine itself will have no direct effect on menopause or hormone levels.

RELATED: The best diet for weight loss

How to avoid phentermine side effects: In both tablet and capsule oral dosage forms,

Phentermine comes in both tablet and capsule oral dosage forms. Daily dosing ranges from 15 to 37.5 mg, with 37.5mg as the maximum daily dosage. It has been marketed under various brand names and dosing strategies, including Adipex-P and Lomaira. Data has shown that some side effects occur significantly more frequently in people taking higher doses of phentermine. Dryness of the mouth, anxiety, insomnia, and abdominal pain are among the potential adverse effects that may happen more frequently at higher doses. If phentermine is the right drug choice, the lowest effective dose should be taken to minimize side effects.

Do not combine phentermine with other stimulants or weight-loss drugs; there is no good evidence of safety or efficacy and the potential for a dangerous drug interaction may exist. This includes over-the-counter herbal products and dietary supplements as well. We also don’t know the full effect of phentermine drug interactions with other CNS active drugs, such as selective serotonin reuptake inhibitors (SSRIs), a popular class of antidepressants. Phentermine has not been shown to interact with hormone replacements or birth control. Talk to a pharmacist or healthcare professional before combining these classes of medication to learn about additional possible risks. 

Phentermine is contraindicated with monoamine oxidase inhibitors (MAOIs), such as selegiline. The drug interaction that results from the concomitant use of phentermine and MAO inhibitors can cause serious side effects, including hypertensive crisis. 

Phentermine is only intended for short-term use and is typically limited to a few weeks. Long-term use of phentermine could lead to increased risk and the occurrence of adverse events. While the most common side effects of phentermine are usually self-limiting with short-term use, there are life-threatening side effects, such as hypertensive crises, that can occur. Blood pressure and heart function should be checked regularly while on phentermine. If blood pressure increases while taking phentermine, seek medical help. Speak with a healthcare provider and discuss a strategy for discontinuing the drug. While short-term use is not correlated with high rates of withdrawal symptoms, symptoms like dizziness or tremor could occur.

Phentermine alternatives

Phentermine may not be an option for every woman. Women with a history of heart disease or who are determined to be at high risk for heart disease are not candidates for phentermine treatment. However, there may be other, safer weight-loss options for these patients. It’s important to remember that almost all weight loss therapies are intended to be used with a healthy diet and exercise regimen. If phentermine is not proving to be an effective weight reduction treatment, that is also a reason to seek alternative therapies. Phentermine should never be taken if an allergic reaction to phentermine or a related drug has occurred. Seek medical attention immediately if an allergic reaction occurs.

The chart below is meant to provide potential alternatives to phentermine to discuss with a healthcare provider. This is not intended as medical advice. There are other drugs with possible uses in obesity not listed here, as their use is considered off-label in obesity. This indicates the Food and Drug Administration (FDA) has not approved the medicine for the indication of obesity, but anecdotal use suggests some potential benefits for obesity. A doctor can also discuss those options and provide more information.

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What can I take instead of phentermine?
Drug name Uses Discounts
Tenuate 

(diethylpropion)

 Short-term obesity treatment Tenuate coupons
Qsymia 

(phentermine and topiramate)

 Long-term obesity treatment Qsymia coupons
Contrave 

(naltrexone and bupropion)

 Long-term obesity treatment Contrave coupons
Saxenda 

(liraglutide)

 Long-term obesity treatment Saxenda coupons
Wegovy 

(semaglutide)

 Long-term obesity treatment Wegovy coupons