Phentermine Side Effects and How It Affects Females

Key Takeaways

• Phentermine can help with weight loss, but it carries unique risks for women’s health and hormones.
• Phentermine is not safe for use during pregnancy or breastfeeding, and effective contraception is essential while taking the medication.
• Menopause-related weight gain may lead some to consider Phentermine, but its stimulant nature requires careful evaluation of cardiovascular health.
• Always consult with a healthcare provider before starting Phentermine and closely monitor for any adverse effects to ensure it’s safe for your needs.

{{mid-cta}}

‍

It seems like medical weight loss drugs are everywhere these days. From celebrities to your next-door neighbor, taking a prescription to lose weight seems less of a hushed topic than in the past.

Weight loss medications aren't new, but they all work differently in the body. One that's been around for a while is Phentermine. Phentermine is an FDA-approved medication that suppresses appetite, so calorie intake drops. A pill that makes you less likely to overeat may sound enticing, especially for people who've tried to lose weight without success.

Still, it's essential to understand the potential side effects of Phentermine before taking it. This is especially true for women, as women's bodies are especially sensitive to rapid weight loss and restriction.

Here's what you need to know about Phentermine's side effects and why taking it for weight loss is more complex than it may seem.

What is Phentermine?

Phentermine, known as a sympathomimetic anorectic or anorexigenic, is prescribed to facilitate weight loss by acting as an appetite suppressant. It has brand names like Adipex-P and Lomaira and lower-cost generic options.

Phentermine is closely related to amphetamines (and also carries similar risks of addiction), so it's considered a controlled substance by the FDA and isn’t designed for long-term use.

In the '90s, "fen-phen," a combination of Phentermine and fenfluramine, was sold as a quick fix for weight loss but quickly taken off the market after being linked to heart valve damage and fatal pulmonary hypertension.  Phentermine alone does not appear to have the same severe side effects, although there is still a potential for serious side effects, as you'll learn below.

The way Phentermine works for weight loss isn't completely clear, but experts believe there are two primary mechanisms. First, Phentermine may increase the production of neurotransmitters (chemical messengers in the brain) like dopamine and norepinephrine that lower food cravings and appetite.¹

Second, it reduces appetite by activating the nervous system to release chemicals called catecholamines that influence appetite and metabolism. Metabolic activity, including breathing and heart rate, also increases. Weight loss occurs due to taking in less food and possibly burning more energy.¹

<div class="pro-tip"><strong>Also Read: </strong><a href=weight-loss-myths>Weight Loss Myths Debunked</a>.</div>

Common Side Effects of Phentermine

People taking Phentermine should be monitored while taking the medication and be aware of potential side effects. Understanding the possible adverse health impacts can help you weigh the risks or benefits with your healthcare provider.

Common side effects include:^{1, 2}

• Headache
• Insomnia and trouble sleeping
• Heart palpitations or irregular heartbeat
• Constipation or diarrhea
• Vomiting or nausea
• Dizziness
• Dry mouth
• Hair loss
• Sexual side effects

Impaired judgment and driving or ability to operate machinery are also listed as potential concerns with Phentermine.³

Serious Side Effects of Phentermine

Serious side effects are rare but can happen.  These side effects include allergic reactions, severe mood changes, heart health, and neurological concerns.

Severe side effects include:^{1, 4, 5}  

• Seizures or shaking
• Blurry vision
• Weakness
• Uncontrolled muscle movements
• Behavioral changes
• Increased heart rate and high blood pressure
• Heart valve disease
• Lung disease (primary pulmonary hypertension)
• Tachycardia
• Cardiac ischemia
• Addiction and withdrawal symptoms
• Psychosis

People with a history of addiction or heart problems should not take Phentermine.

If you notice any symptoms like chest pain, trouble breathing, fainting, or leg swelling, it’s recommended to stop taking Phentermine and seek medical attention immediately.

Interactions with Prescription Drugs and Medical Conditions

People with certain medical conditions like hyperthyroid (overactive thyroid), glaucoma, high blood pressure, or kidney dysfunction should avoid taking Phentermine. 

Drug interactions are also possible with certain antidepressants (especially monoamine oxidase inhibitors), blood pressure medications, and other stimulants. If you take any over-the-counter supplements, make sure to share them with your doctor to get proper medical advice. 

How does Phentermine Affect Females?

Women’s hormones are particularly sensitive to stress. Diet drugs like Phentermine, combined with very low-calorie diets, can introduce physiological stress that may disrupt delicate hormone systems. 

Here are some ways that Phentermine can impact females.

Phentermine and Periods

Your body needs a certain number of calories for basic but essential functions like breathing or thinking, so if calories drop too low or the body is under stress, it limits the activity of so-called non-essential functions like sex hormone production, which control your period. 

As the production of these hormones drops, the menstrual cycle can be disrupted, irregular, or absent. Anytime you stop having a period (and aren't pregnant or in menopause), seeing a doctor is a must.⁶

Phentermine and Birth Control

Phentermine has been linked to an increased risk of congenital disabilities that can develop early in pregnancy—even before you realize you are pregnant. Additionally, weight loss during pregnancy may harm an unborn baby. For these reasons, using effective birth control is essential while taking this medication.⁷

While Phentermine doesn’t impact the effectiveness of birth control, it can cause spotting (breakthrough bleeding) while taking birth control pills.

Phentermine and Pregnancy

Phentermine is not safe to use during pregnancy, and it’s never recommended to lose weight during pregnancy. Adequate food and nutrients are essential to support the growing baby and mother during pregnancy.

Weight loss may support fertility before pregnancy, although studies are mixed on whether using Phentermine increases conception rates. However, it’s essential to use contraception while taking Phentermine. If you are planning to become pregnant, discontinue Phentermine before trying to conceive.^{8, 9}

Phentermine and Breastfeeding

Phentermine is not well-studied in breastfeeding, and its potential effects on both the nursing parent and the infant remain unclear. Healthcare providers typically avoid weight loss medications as they may pass into the breast milk.

Maintain a well-balanced, nutritious diet to support a gradual, healthy postpartum weight loss. For those who may need additional support with weight loss, Phentermine or other similar medications is an option best explored after breastfeeding has concluded. 

 Phentermine and Menopause

Menopause often brings changes to the body, including hormonal shifts that can lead to weight gain or make it harder to lose weight. These challenges may lead some individuals to explore weight loss aids, such as Phentermine.

While Phentermine can be effective for losing weight, it’s essential to be cautious, especially during menopause. Since Phentermine is a stimulant, it can impact cardiovascular health, an important consideration as the risk of heart disease and changes in blood sugar goes up during menopause. 

The Bottom Line

Phentermine may support weight loss, but it’s essential to understand its potential side effects and unique risks for females from pregnancy through menopause. Anyone with a history of addiction or heart problems should avoid Phentermine. Always consult a healthcare professional to determine whether Phentermine is safe for you. 

<div class="pro-tip"><strong>Learn More: </strong><a href=ozempic-vs-phentermine>Ozempic vs Phentermine for Weight Loss: Key Differences</a>.</div>