Phentermine Side Effects In Females (miscarriages, period issues)

January 9, 2024 |

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Phentermine is an FDA-approved obesity drug, but be careful when taking it if you’re female because it has side effects that could potentially harm you and your baby if you’re pregnant or breastfeeding.

Using phentermine during the first and second trimesters can increase the risks of prenatal fetal stroke. That could lead to permanent birth defects or even a stillbirth.

Studies on whether phentermine use can increase a woman’s risks of miscarriage and birth defects are limited and have conflicting results though.

Although one study found no pattern of birth defects, malformation, or miscarriage in pregnant women using phentermine/fenfluramine during the first trimester, you might want to avoid the possibility altogether.

Considering that a miscarriage is a heartbreaking and even potentially life-threatening experience, we recommend that you avoid using phentermine if you’re pregnant or planning to have a baby.

Other side effects of phentermine in females include:

  • Bleeding with birth control
  • Postpartum bleeding
  • Depression
  • Nausea
  • Hair loss
  • Effects on your menstrual cycle

Why does phentermine cause these problems in ladies? Is there a way to prevent these side effects and continue using phentermine?

Let me share with you what I learned while researching this topic.

Phentermine Side Effects In Females

1. Phentermine Side Effects With Birth Control

Studies about the interactions because phentermine and birth control are limited. However, the drug can cause spotting if you’re on birth control. Although it isn’t likely to cause massive, uncontrolled bleeding, spotting can be worrisome.

Be sure to inform your doctor if you have spotting or a heavier period than usual, particularly if you also experience seizures or other adverse effects.

2. Phentermine Side Effects With Pregnancy

Although phentermine use is believed to increase a pregnant woman’s risks of miscarriage, birth defects, and prenatal fetal stroke, a study showed that this might not be the case.

Could it be a case of phentermine being mistakenly linked to these pregnancy issues? Well, considering that the studies on phentermine use and pregnant women are limited, it’s really hard to tell which is which.

However, if phentermine really causes these problems, it’s best to stop taking this drug until you give birth.

You don’t want to risk your baby’s life just trying to prove whether phentermine is good or bad for pregnant women.

If you still aren’t convinced, the FDA classifies phentermine (brand name SUPRENZA) as a “Pregnancy Category X” drug, which means that it can cause a potential hazard to your unborn baby.

Another phentermine brand (in combination with topiramate), Qsymia, discloses on its official website that the drug could cause serious side effects, including birth defects such as cleft lip and cleft palate). Those taking phentermine are advised to use effective birth control and monitor for a possible pregnancy every month because the defects can start even during early pregnancy.

Due to its possible adverse effects on your developing fetus, its risks could far outweigh its benefits.

So, it’s not recommended for use during pregnancy.

The FDA also points out that there’s a minimum weight gain currently recommended for all pregnant women, even if they’re already overweight or obese. As a weight-loss drug, phentermine isn’t ideal for pregnant women.

As sad as it might sound, you can’t really try to lose weight when you’re pregnant.

3. Phentermine Side Effects After Giving Birth (Postpartum)

Phentermine can cause complications such as bleeding during surgery or other medical procedures. It could also happen after you give birth.

If you had a C-section, it might be best to wait until around 4 months post-delivery before resuming your phentermine intake, just to be sure it won’t cause bleeding or other complications.

4. Phentermine Side Effects while Breastfeeding

Phentermine can be excreted in breast milk.

Although there have been no reported side effects on babies, remember that the drug can be dangerous to adults because it’s a stimulant that has the potential to be addictive. Considering that it’s excreted in breast milk, phentermine might affect your baby’s developing brain.

There’s also no way of knowing how much of this drug is excreted in breast milk.

Based on the known side effects of this drug in adults, possible side effects for your baby might include agitation, tremors, or decreased feeding. It might also affect their sleeping patterns as they could experience insomnia-like symptoms.

It could become dangerous to your infant if you consider the possibility of the drug affecting their heart or causing increased blood pressure, similar to what adults might experience.

Also, remember that phentermine suppresses your appetite. Taking it while you’re breastfeeding might affect your calorie intake, which could reduce your breast milk supply.

So, it’s really a good idea to avoid using this drug if you’re breastfeeding, unless you decide to stop breastfeeding instead.

5. Depression in women

Studies show that phentermine use can lead to depression.

Women with low levels of estrogen are more likely to experience episodes of depression. This is believed to be linked to estrogen possibly boosting levels of serotonin, the body’s “feel-good” hormones.

That’s why estrogen deficiency could lead to depression.

Since neurotransmitters and hormones like estrogen share common pathways and receptor sites in the brain, the increase in neurotransmitters in the brain due to phentermine’s stimulant effects can decrease estrogen levels.

Depression is no joke. Some women suffering from phentermine-induced depression might even entertain suicidal thoughts or experience rage and anxiety attacks.

It’s also important to note that as a stimulant, phentermine can amplify feelings and emotions. This could affect how you respond to a situation, which can be different from what you would have normally done.

So, that means that it might even magnify your feelings of anger, guilt, and depression. The drug might also lead you to feel irritable, agitated, or display other abnormal behaviors.

Patients with a history of clinical depression are more susceptible to suffering this side effect due to phentermine use. It’s important to tell your doctor about your medical history so they can monitor for possible signs of a mental health problem.

The earlier you receive treatment, the better.

6. Nausea

It’s also common for phentermine users to experience nausea, dizziness, and drowsiness. So, it’s best to avoid driving or operating dangerous machines if you’re taking this drug.

Watch out for other symptoms that you might experience with nausea because that can signal other more serious side effects.

For example, if nausea is accompanied by fast breathing, rapid heartbeat, restlessness, abdominal or stomach pain, eating problems, and muscle tremors, call your doctor right away. These could be symptoms of metabolic acidosis or having too much acid in your blood.

Prolonged acidity in your blood can be dangerous. Seek treatment immediately.

7. Hair Loss in females

A number of phentermine users experienced hair loss, and it’s something that can cause a lot of worries, particularly in women. Because women have long hair, the hair loss can be more pronounced as you notice too many strands of hair on your brush or the floor.

Hair loss from phentermine could be due to chemotoxicity wherein the components of the drug disrupt certain body systems, such as affecting the growth of your hair follicles.

This could force your hair into the resting phase earlier than they’re supposed to.

More hair in the resting phase means more hair falling off sooner than expected.

The hair loss is also believed to be due to nutritional deficiencies from not eating enough because phentermine is an appetite suppressant.

Another possible reason for the hair loss is that the weight loss could be causing stress on your body. When you’re under a lot of stress, your hair can quickly turn into the resting phase.

It’s even possible that your body will attack the hair follicles as a rare immune response to stress.

If you notice yourself pulling your hair due to stress, stop. It can be habit-forming and could further lead to more hair loss.

Phentermine Side Effects in Menstrual Cycle

Phentermine and other diet pills for that matter could affect your menstrual cycle, leading to irregular periods or sporadic spotting throughout the cycle.

Menstrual irregularities aren’t listed as an official phentermine side effect but a lot of women reported experiencing this while taking the drug.

Some of the period irregularities that women experience can include:

  • Lighter or heavier periods
  • Shorter or longer periods
  • Early (6 or more days earlier than expected) or late periods (more than 5 days late)
  • Extra or missed periods
  • Worse PMS symptoms, including nausea, cramps, dizziness, etc.
  • Spotting or intermittent bleeding between periods
  • Postmenopausal bleeding

Studies on why phentermine affects the menstrual cycle are limited.

However, it is believed to be due to any or a combination of the following:

  • Inadequate nutrition or dietary changes could disrupt your period and cause these other symptoms due to deficiency in certain fats, nutrients, proteins, and calories in your diet.
  • As a stimulant, phentermine affects your central nervous system, releasing more epinephrine (adrenaline), dopamine, and norepinephrine. These hormones can actually affect the menstrual cycle, especially when coupled with extended periods of stress (rapid weight loss can make your body feel stressed).
  • A dramatic weight loss that you might experience with phentermine use can also disrupt other hormones, including estrogen. These hormonal changes can directly affect your period because estrogen is responsible for the menstrual cycle.

Phentermine Side Effects In Females & Bleeding

You might have heard of phentermine causing bleeding in some women, particularly with prolonged use.

The good news is that phentermine use isn’t likely to cause heavy bleeding that could lead to a hemorrhage. However, it could still cause breakthrough bleeding or spotting, particularly if you’re using birth control pills.

However, heavy bleeding is still a possibility. It’s a less common side effect, but something that you should definitely watch out for.

If you notice frequent spotting or irregular bleeding outside your regular period schedule, be sure to tell your doctor.

Although the blood loss isn’t likely to be dangerous (unless it’s heavy bleeding), it can still be significant enough to lead to other problems, such as anemia (lack of healthy red blood cells to carry enough oxygen to your body’s tissues).

Some anecdotal reports shared by female phentermine users made us feel worried:

“I’ve been on Phentermine for 3 months. I had a normal not-as-heavy period for my December cycle, then shortly after it ended I started spotting now a week before it’s due I’m having another period. A heavy period with clots and all (that’s not unusual). They should make this a listed side effect because it seriously has me worried 🙁 .” – Roxie

Here’s another:

“Hi, I started Phentermine when my period started. Its been a month and my period hasn’t stopped. No cramps no pain, but regular bleeding. I had an ultrasound and an expert gyno opinion, but they said everything is normal. My thyroid was normal too. My cycles were normal but it’s like irritating now since I am bleeding all the time. I stopped phen a while ago but the bleeding isn’t stopping.” – Aamir

How to Avoid Phentermine Side Effects in Females

Not everyone experiences all the side effects listed above, yet many of them can cause you unnecessary worry, particularly if it involves bleeding or, worse, a miscarriage and birth defects.

Let’s talk about what you can do to help avoid these phentermine side effects below.

1. Eat Healthy Foods

Phentermine is an appetite suppressant, so you can expect it to affect how much you want food. It even suppresses your cravings.

However, you can choose to eat healthy foods to boost the effects of phentermine and also reduce the side effects mentioned above. It’s also not a good idea to skip meals.

Here are some healthy foods to focus on when you’re on phentermine to avoid these side effects:

  • Lots of water
  • Proteins
  • Healthy, high-fiber foods
  • Fruits and vegetables
  • Alkalizing foods

Plus, diets high in calcium, vitamin D, and omega-3s but low in caffeine and salt are known to help reduce PMS symptoms and help regulate your menstrual cycle.

It’s also a good idea to increase your intake of iron-rich foods, especially if you’re bleeding more than usual.

Some foods can worsen your side effects. Avoid these as much as possible:

  • Sugar and simple carbs
  • Processed meats
  • Junk foods
  • Alcohol
  • Acidifying foods
  • Foods with trans-fats

2. Exercise

Phentermine can actually increase your energy levels with its adrenaline-boosting effects. You can use this extra energy to work out.

Plus, regular exercise can do wonders for your menstrual cycle and help you manage period cramps, which feel more intense with phentermine use.

Take up an exercise that you love, such as dancing with Zumba, doing some yoga, taking a swim, or simply taking a walk in the park.

3. Quitting Phentermine (yes!)

So, phentermine is giving you all these troubles and the side effects just won’t go away. You might also feel worried that you’re pregnant and the drug could cause birth defects, miscarriage, or a stillbirth.

Why not just quit using phentermine?

For some people, quitting phentermine might just be the only solution to help them avoid the side effects that the drug can cause.

Talk to your doctor before stopping phentermine use. You might need to slowly reduce the dose over a period of several days to avoid severe side effects or withdrawal symptoms.

Another option is to switch to a safer weight-loss pill that doesn’t cause the side effects listed above.

Let’s dive into that safe option below.

Safer Phentertime alternative (without side effects)

Worried about phentermine’s side effects? Well, PhenQ could be a better alternative to the worrisome phentermine. It’s an effective appetite suppressant like phentermine, but without the side effects in females mentioned above.

Like phentermine, PhenQ suppresses your appetite, crushes your cravings, and boosts your energy level, but it also has other features that make it a much better option:

This phentermine alternative is made of 100% natural ingredients. It doesn’t interfere with oral contraceptives or causes bleeding if you’re on birth control.

You can also buy it over the counter instead of regularly going to your doctor for a prescription.

Plus, it can improve your mood (phentermine can cause depression) and burn stored fats (phentermine suppresses appetite but doesn’t target fat burning).

And the best thing about PhenQ is that it isn’t potentially addictive and it doesn’t cause the side effects normally associated with phentermine. So, you can use it for a prolonged period without worrying.

You can also stop anytime, and resume anytime.

No worrying about withdrawal effects, unlike phentermine, which is a scheduled drug.


What Does Phentermine Do To Your Hormones?

Phentermine doesn’t directly cause hormonal imbalance or affect hormones like estrogen.

However, it can indirectly do so because a sudden drop in weight can increase the likelihood of hormonal imbalances.

Also, take note that neurotransmitters and hormones (e.g., estrogen) share common pathways or receptor sites in your brain. When neurotransmitter levels are increased due to phentermine’s stimulant effects, it can decrease your estrogen levels.

If you’re taking birth control pills, phentermine can make your body process estrogen from these pills more quickly.

It’s believed to be one of the reasons why you can experience spotting or breakthrough bleeding.

Note that it can decrease the estrogen levels in the pills because they’re processed more quickly. This could lead to reduced efficacy of your birth control pills.

Can A Pregnant Woman Use Phentermine?

Phentermine is classified as a “Pregnancy Category X” drug, which can potentially harm your unborn baby. So, it shouldn’t be used by pregnant women.

Although studies have conflicting results, there have been some reports of this drug causing birth defects, stillbirth from a prenatal fetal stroke, and miscarriages.

Phentermine/topiramate brand Qsymia could also cause birth defects such as cleft lip and cleft palate.

Can You Take Phentermine After Giving Birth?

Due to its stimulant effects, phentermine might cause increased bleeding after surgery or a medical event like giving birth. It’s best to wait at least 2-4 months after delivery before resuming phentermine use.

Always consult your doctor before deciding to use phentermine again.

Does Phentermine Cause Period Issues?

Yes. Plenty of women have reported experiencing increased period pain or cramps, irregular menstruation, lighter or heavier bleeding, early bleeding, delayed bleeding, breakthrough bleeding or spotting, and other period issues.

Does Phentermine Affect Estrogen?

It could lead to decreased estrogen levels in the body due to the reduced availability of receptors in the brain because of increased neurotransmitter levels (they share the same receptors).

Phentermine also causes the body to process estrogen in birth control more quickly than it should.

When Can A Woman Safely Take Phentermine?

Considering its effects on the body, it’s hard to tell if phentermine can truly be safe for a woman to use, particularly since it affects the menstrual cycle – and that’s a monthly thing.


Phentermine side effects in females are numerous and should be considered before taking the medication. Birth control pills may increase the risk of bleeding, miscarriage, and depression.

Nausea and hair loss are also common side effects.

Most importantly, phentermine can interfere with your menstrual cycle and cause period changes. If you are considering taking phentermine, make sure to discuss all potential side effects with your doctor.

There are also safer and healthier alternatives available that have similar weight loss results.

For example, PhenQ is a weight loss supplement that has been shown to help people lose weight safely and effectively without many of the dangerous side effects associated with phentermine.

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