How Phentermine Affects Your Period

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Periods are a pain, literally, but we kind of like them being regular so we can anticipate when to schedule in the necessary couch-days and Netflix marathons. However, when you’re taking phentermine, your period can become irregular and your monthly symptoms may worsen due to the way phentermine affects your hormones. Here we explain how phentermine affects your period, and how to cope with these changes.

How Phentermine Affects Your Period

Although it is not listed as a side effect of phentermine, anecdotal evidence shows that many women experience changes to their period when taking the medication. Discussions in the Facebook support group indicate that the following changes have all been experienced by our phentermine users:

  • Missed periods (no menstrual flow for over 40 days)
  • Late periods (5 or more days overdue, according to usual cycle)
  • Early periods (5 or more days early, according to usual cycle)
  • Heavier or prolonged periods
  • Lighter or shorter periods
  • Spotting or intermittent bleeding between periods
  • Infrequent menstruation (only 4 to 9 periods in a year, medically known as Oligomenorrhea)
  • Frequent menstruation (more than 17 periods in a year, medically known as Polymenorrhea)
  • More severe symptoms – cramps, premenstrual syndrome (PMS), nausea, dizziness,

Essentially, these changes to your period all indicate irregular menstruation, whereby your monthly cycle and the symptoms which occur alongside it are different to the menstruation cycle that you used to experience before taking phentermine.  While these changes can be very concerning, we hope that knowing that many other women have experienced the same symptoms when taking phentermine helps to put your mind at ease – which is why the Facebook support group is such an important source of information and support for many phentermine users.

Why Does Phentermine Affect Your Period?

In much the same way that phentermine has been indirectly linked to hair loss, it is thought that the changes to your period occur alongside phentermine due to the way that weight loss can affect your hormones, which in turn affects your monthly cycle. Dramatic weight loss, which phentermine users often experience, causes a drop in the amount of estrogen in the body, as the release of estrogen is partially based on the amount of fat cells in the body. This decline in estrogen production can then cause changes to your menstrual cycle, resulting in irregular periods and can even cause your periods to stop completely.

An alternative theory is that the way in which phentermine stimulates your sympathetic nervous system to trigger the ‘fight or flight’ response can result in a reduction in the release of reproductive hormones, which would explain why some women taking phentermine may experience fewer periods than usual. However, irregular periods, heavier menstrual bleeding and spotting can also be explained by the way that phentermine in known to increase your heart rate. A faster heart-rate means increased blood flow and more build up in the ‘spiral arteries’ which support the endometrium of your uterus, which then degenerates to cause the onset of your period.

Another reason for an abnormal menstrual cycle is poor nutrition as a result of not eating a varied enough diet, possibly due to a lack of appetite while taking phentermine. Regardless of your weight or the amount of exercise you do, a lack of iron, zinc, and healthy fats in your diet can all cause changes to your period and an increase in the severity of menstrual symptoms such as cramps, dizziness and nausea.


How To Reduce These Symptoms

If you think that poor nutrition is contributing to your menstrual irregularity then taking a comprehensive multivitamin such as Phen Vites alongside your phentermine prescription will ensure that you’re getting all the nutrients you need for a healthy body, and this will also help to ease the symptoms of irregular periods, menstrual cramps, and other symptoms. In fact, making sure to get all the vitamins and minerals you need to keep healthy will also boost weight loss, as your body needs a variety of nutrients to burn calories and keep your metabolism going. As well as taking a multivitamin, you should try to eat a varied diet, being sure to include healthy foods rich in iron such as leafy greens, lean red meat and pumpkin seeds to help reduce some of these menstrual symptoms.

If you are sexually active and able to become pregnant then you should be using some kind of birth control as phentermine cannot be taken by women who are pregnant or trying to become pregnant. If your choice of contraceptive is an oral birth control pill then taking the pill continuously is one way to limit severe periods and other symptoms that come with menstruation, such as PMS and cramps. This method is often recommended by medical professionals to women with heavy or painful periods, but they do advise that you should have at least four periods a year to maintain the correct balance for future fertility. So, instead of taking the placebo pills or skipping your pill for a week, just move onto your next packet, but just be sure to give yourself a break from your birth control pill every couple of months. Avoiding having a period every month means that you will be able to get some relief from the effects that losing weight with phentermine can have on your menstrual cycle. Not to mention, skipping several periods can also help you to avoid the other symptoms of that time of the month, such as weight gain, bloating and cravings, so staying on track while taking phentermine is much easier too.

Lastly, if your period is often irregular and you have had difficulty losing weight in the past, as well as other symptoms such as fatigue, cramps, constipation, fertility problems or acne, then you may be suffering from an undiagnosed health issue, such as thyroid problems or Polycystic Ovary Syndrome (PCOS), which both affect the body’s hormone levels. Although losing weight with phentermine can help to relieve some of the symptoms of these conditions, it is advisable to be tested for these conditions, if only to rule them out as possibilities.


Although coping with irregular periods and more severe symptoms can be difficult, getting healthier by eating a more varied diet and losing weight with phentermine will help to resolve these issues in the long term. The good news is that when you get closer to your target weight your body should adjust to the new amount of hormones, and your periods should become more regular and the symptoms less severe.

Have your periods changed since you starting taking phentermine? Let us know by commenting below.

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122 Responses

  1. I started phetermine on 4/3/18 I have lost 11 lbs. I am currently using nexplannon birth control and have never had a period with it but since I started taking phetermine I am now experiencing spotting and some light bleeding and cramping. This would be my normal period time so I assume all is normal.

  2. Hi, i started Phentermine when my periods started. And since then it is being a month i have not stopped my periods. No cramps no pain but it is regularly bleeding. I had an untradound and an expert gynae opinion but they said i have everything normal. My thyroid was normal my cycles weee normal but its like irritating now since i am bleeding i stopped phen for a while but the bleeding isnt stopping. The medicine is not registered in my country but as i am a doctor myself so i asked a friend to send it to me from uk.

    • i have the same problem. have had a period for a month. no sign of stopping. no cramps/no pain like normal….bleeding is super light with 3-4 days of a few clots 1x a day. but it just will not stop! Gyn put me on progesterone for 10 days. on day 5 and still hasn\’t stopped. I guess i have to stop the Phen. It is working so i don\’t want to stop it…. did yours ever resolve? i see your post was from April.

  3. I took phen about 3 yrs ago no prob. I started back in middle of feb and since then every 2 weeks, for over 2 weeks, i have had menstrual bleeding. I have gone to my obgyn in hopes to find the issue. Blood test and thyroid is normal. Only explanation is the pills. I have lost 25 lbs so far but i can not continue to use these pills if this is the emotional and physical burden they will cause me. Light spotting that turns into heavy, brighr, blood cloths. Would lowering the dosage help?!

    • Hi Tia! We’re sorry to hear about your abnormal periods 🙁 We would recommend speaking with your prescribing doctor to see if he/she thinks lowering the dose would help. He or she is a medical professional, and more familiar with your specific case/medical history, so he/she would be better able to assist you in working through this reaction. Best wishes!!

  4. I start taking it on may, i was expecting my period the 24th of June, and it’s been 11 days and nothing, I done like 7 pregnancy test and all of them are negative. What do i need to do?

    • Hi Tatiana! We’d recommend speaking with your doctor if your period still hasn’t come.

  5. I’ve taken it off and on for the past 4 years and it always seems to make me start my period 2-3 days early. I’m not complaining since I’m normally 2-3 days late most months. But for the ladies that take it and miss their period or it’s delayed, I would suggest not taking it anymore. The stress and hassle of constantly thinking about when you’re gonna start, would drive anyone insane.

  6. I’ve been taking them on and off since January. My first period while on them was kinda heavy and longer than 5 days. It wasn’t heavy the entire duration, so that was a relief. However the past 3 months my period has been somewhat non existent. I will cramp and will have light bleeding for about a day or two. This past month the cramps were terrible(which is unusual for me) and I bled one day. I will look into a multivitamin & a more balanced diet

  7. Hi my name is T
    I have late period last month but soon I start duromine 30mg then in the afternoon same day I have my period. Very light bleeding but carry on for 8days. Then stop for 2days. No pads need. On the 11days of duromine my period start again. I can see very red when I pass my urine but not on pad. I don’t know why. I only loose 2-3kg in 11days. Done lots of excersie and appetite become less too. I have hasimoto thyroid problems too. Drunk lots of water. Constipation. Dry mouth. Full of energy. Can you give me some advice pls.

    • Hi T, 2-3kg in 11 days is really impressive weight loss – congrats! If your side effects and spotting continue or get worse, we would recommend speaking with your prescribing doctor. He or she is best able to assess what’s causing the negative reactions and work with you to develop an individualized plan to address them. Best wishes!

  8. Tatiana, what ever happened? I’m in the same exact boat!

    • I\’m experiencing the same thing except I\’m only 4 days late., But I am NEVER LATE 😩 always a 28 day cycle

  9. I’ve been taking it since October 20th. I’m down 22 pounds. My last period was December 19th but now it’s started again. I’ve never had breakthrough bleeding.

  10. I have been on and off adipex for years. After having my daughter in 2013 and stopping breastfeeding in 2014 I got back on birth control and adipex in 2014. I had regular periods for awhile, but for the last 3 years I haven\’t had a period at all which I thought was caused by my birth control pill, but I think adipex caused it. Last Thursday, 1/03/2019, I started back on adipex after being off of it for 4 months and I am still on birth control too and on 1/03/2019 my period came full force in the middle of my birth control pack. No discomfort, but this is a moderate flow and today is day 5 with no end in sight for this cycle after 3 years of no period. I need to lose this weight, but I sure did enjoy not having a period for 3 years and I wish this period would end already considering I am taking my pill every day!!!

  11. I’ve been on duromine for 12 months straight and have not had a single period in the whole time is that a concern? I don’t really care to be honest but obviously if my health is at risk?

    • Hi Amber, we’d recommend checking-in with your doctor given that you’ve missed more than three periods in a row. Best wishes!

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