Phentermine and Your Period

Periods are a pain, literally, but they are a natural part of life, and most women like the predictability of a monthly cycle. Unfortunately, some female phentermine users experience early, late, missed, heavy, or especially uncomfortable periods, or spotting, while taking this medication.

Menstrual irregularities are not listed as an official phentermine side effect, but anecdotal evidence suggests that phentermine period problems are a common concern for female patients.

How Phentermine Affects Your Period

woman with menstrual cramps
Some women experience menstrual cycle changes while taking phentermine

Although it is not listed as a common side effect of phentermine, about 1 in 8 patients experience phentermine period problems, according to a recent online poll ( 1 ).

Some of the menstrual cycle changes that users report while taking this medication include:

  • Early or late periods
  • Extra or missed periods
  • Lighter or heavier periods
  • Shorter or longer periods
  • Spotting (intermittent bleeding) between periods
  • Worse PMS symptoms such as cramps, nausea, dizziness, etc.
  • Postmenopausal bleeding

A period is “early” if it occurs 6 or more days earlier than expected and “late” if it comes more than 5 days late. A “missed period” is no menstrual flow for more than 35 days.

Why Does Phentermine Affect Your Period?

woman waiting nervously for the results of a pregnancy test
One of the most-reported phentermine menstrual cycle changes is a late or missed period

Scientific evidence does not indicate that phentermine or other stimulants can directly disrupt a woman’s menstrual cycle. Still, many female patients experience notable menstrual irregularities.

In the absence of a clear, scientific answer, three basic theories stand-out as explanations for why phentermine affects your menstrual cycle:

1. Dramatic Weight Loss

The most likely explanation for phentermine period problems is hormonal changes related to weight loss.

Estrogen levels, in particular, drop with weight loss. Estrogen is the primary hormone responsible for regulating the menstrual cycle, so a sudden decline in estrogen due to weight loss (or increased exercise) can disrupt your period.

Too much or too little estrogen can cause menstrual changes, including infrequent or missed periods, or unusually light or heavy flow ( 2 ).

2. Taking a Stimulant

As a central nervous system stimulant, phentermine also affects another group of hormones called catecholamines. These hormones, including dopamine, epinephrine (adrenaline), and norepinephrine, also help regulate the menstrual cycle ( 3 ).

Catecholamine levels skyrocket during periods of stress, and we know that excess stress disrupts the menstrual cycle, so medications (like phentermine) that simulate a similar stress response may also affect a woman’s period.

3. Dietary Changes

Another reason for an abnormal menstrual cycle is inadequate nutrition.

Intake can be deficient in terms of calories, fat, protein or micronutrients, or a combination of multiple factors. Unfortunately, eating too little can disrupt your period and increase the severity of menstrual symptoms such as cramps, dizziness, and nausea.

Overly-restrictive diets like Keto tend to prove especially problematic. In fact, “menstrual dysfunction” is the second most common side effect of medically-supervised keto diets, second only to weight loss ( 4 ).

How to Combat Phentermine Period Problems

Talk to a doctor if phentermine period problems are serious, worsening, or interfering with your daily life.

Individual phentermine period problems range from mild to severe, so how you approach them should vary depending on their severity.

If your symptoms are relatively mild, consider lifestyle changes that combat PMS and may help alleviate some common phentermine period problems. However, for more serious phentermine menstrual cycle issues, schedule an appointment with your prescribing doctor or gynecologist ASAP so that the two of you can work together to find a solution.

Here are three ways you can deal with phentermine period problems:

Modify Daily Habits

A healthy diet and exercise habits can help reduce and even prevent phentermine period pain.


Studies show that diet can have a significant impact on hormone levels, and, therefore, period pain.

For example, eating a low-fat, high-fiber diet is associated with lower estrogen levels ( 5 ). So, women that follow a low-fat, vegetarian diet tend to experience significantly less PMS and menstrual pain ( 6 ).

A diet high in omega-3s, calcium, and vitamin D, and lower in salt and caffeine, can also help reduce PMS symptoms ( 7 ).

If you’re bleeding more than normal from a phentermine-heavy period, incorporate a variety of healthy, iron-rich foods – such as lean red meat, dark leafy greens, and pumpkin seeds – into your diet to reduce the risk of anemia.


Even though staying curled up in a ball on the couch may sound more appealing, exercise is a proven strategy to manage cramps and other PMS symptoms ( 8 ).

Aim for at least 30 minutes of moderate activity most days of the week. If phentermine period pain is keeping you out of high-intensity activities, take a short walk, go for a gentle swim, stretch it out with some yoga, or dance away the pain at Zumba.

used packet of birth control pills
Hormonal birth control can help regulate your menstrual cycle and ease phentermine period problems

Consider Birth Control

If your phentermine menstrual cycle is irregular or especially uncomfortable, or if you were experiencing problems even before starting treatment, your doctor may suggest hormonal birth control.

In addition to preventing pregnancy, hormonal birth control methods (such as the combined pill) also make many women’s periods shorter, lighter, and less painful, plus reduce PMS symptoms ( 9 ).

In fact, some pills are designed to allow you to skip up to 75% of your periods and menstruate just four times per year. If your doctor thinks it is a good option for you, skipping a couple of cycles allows you to steer clear of especially unpleasant phentermine period problems, plus other common PMS symptoms like weight gain, bloating, and cravings that can make it harder to stay on track with weight loss.

Rule-Out Other Causes

If your irregular period is accompanied by other symptoms, such as difficulty losing weight, fatigue, cramps, constipation, fertility problems, or acne, an undiagnosed health issue may be to blame ( 10 , 11 ).

Several common conditions, such as polycystic ovary syndrome (PCOS) and thyroid irregularities, affect the body’s ability to regulate hormone levels, which may impact your menstrual cycle. If your phentermine period problems seem more severe, more wide-reaching or longer-lasting than others’, talk to your doctor about getting tested for other potential causes.

Phentermine Period Problems: Exposed

Understanding the relationship between phentermine and your period from a scientific perspective is one thing, but hearing from other women provides even more information in some cases.

Here, 25 real women share how taking phentermine affected their menstrual cycle:

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


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.


I have the same problem. I 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. Now 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….


I took phen about 3 years 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 OB-GYN in hopes of finding the issue. Blood test and thyroid is normal. Only explanation is the pills. I have lost 25 lbs so far but I cannot continue to use these pills if this is the emotional and physical burden they will cause me. Light spotting that turns into heavy, bright, blood clots.


I started taking it in May. I was expecting my period the 24th of June and it’s been 11 days and nothing. I’ve done like 7 pregnancy test and all of them are negative.


I’ve taken it off and on for the past 4 years and it always seems to make me start my period come 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 going to start would drive anyone insane.


I’ve been taking them on and off since January. My first period while on them was kind of 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 nonexistent. 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.


I’ve been taking it since October 20th. I’m down 22 pounds. My last period was December 19th but now it started again on January 4th. I’ve never had breakthrough bleeding.


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 a while, 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. 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!!!


I’ve been on duromine for 12 months straight and have not had a single period in the whole time.


I started using Duromine on 28/06/18. My period came as usual on the 04/07 but has not stopped. It is not as heavy as my usual period but it is concerning as I have never experienced this before. Judging by all the comments this seems to be ”normal” while on phentermine.


I started Phentermine 3 days ago, and I love it so far, however I was a little worried today when I got a heavy period, which is very unusual for me since I’m on Mirena and I get very light periods, last one was only 2 weeks ago!


I’ve been on phentermine for less than a month and my period should have started by now. I went to the doctor last week to get birth control and took a pregnancy test which was negative or the doctor wouldn’t have prescribed the birth control. Well I’m supposed to start the birth control after my period… not sure how to do that if my period doesn’t come? Should I stop taking phentermine for a few days to let my period break through?


I have an IUD with no period for many years but occasional spotting 2-3 times a year MAX! I started phentermine on 6/18/18 and dropped 20 pounds in the first month but with that came a full blown period lasting 7 days and have had the same going on my fourth month now. I was concerned so googled and found it does mess with your menstrual cycle but does that include someone who doesn’t get them because of an IUD? I was thinking about calling my OB/GYN but because they have been tolerable I figure I have just been fortunate to not have a cycle all this time and to let nature take its course.


I just started taking phentermine this month, right before my cycle came. Now it has ended (about 4 days ago) and I have been noticing the spotting. I got really worried because, for the most part, my period is regular 6 day and I’m done.


I started taking phentermine at the beginning of this month (10/04). I was actually about two weeks past due for my period but it’s fairly irregular. Well, eleven days ago, it started. And it hasn’t stopped or slowed. I’m not having any huge amount of clotting or dark blood, like many of the others who have posted, just medium red. Also, it’s not excessively heavy, just a normal medium flow like I would expect in the middle of my usual period. My mood is normal and I don’t feel like I’m having any other unusual symptoms (no cramping, or overeating). My problem is that I would like my period to be over. Like NOW!


I started Phen about a month (haven’t finish a bottle yet) I been feeling fine except for a ”normal” fast heart beat from time to time. Lost 2kg so far but now that I had my period, it is longer than normal. I usually have it for 5 days, but I am on my 10th day now. It is a light flow, but enough to be noticeable as a period. When will it stop? Oh, and 3 days prior to my period starting I woke up one morning with a nasty migraine due to Phen too.


I have been taking Duromine 15mg for 5 days today. I’m supposed to be PM and haven’t had a period for 11 months. So imagine my surprise this morning… Most of the side effects are gone now, so having a period compared to dry mouth, headache and poor sleep is not so bad. Unless it lasts longer than my usual past 3 days.


When I started taking duromine in October my period was very light then November I didn’t get my period and now December am looking forward to my cycle and still hasn’t come up.


I have pretty regular, light periods. I’ve had uterine ablation and tubal ligation done, so no more pregnancies and nice light periods. I had finished my period about 9 days before starting Phentermine. Literally the next day it started up again, and with a vengeance. I’ve been bleeding heavily for 5 days, needing to change a super plus tampon every few hours. Exactly how my periods were before the uterine ablation procedure. I’m willing to put up with it for the weight loss but if it continues I may ask for an iron prescription since I’m prone to anemia.


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 🙁


I bled the whole time on phentermine (a lil over a month). Spotting everyday ruined my sex life! Went to the doctor they ran every test and put me on a 10 day dose of Provera which had me bleeding or pouring I should say huge gallons of blood for about 1.5 weeks (I also quit the phentermine). Now my body is back to normal. I don’t think I would’ve ever stopped spotting/bleeding had I continued phentermine. I also learned I had high blood platelets which I’m sure was connected with the drug. I want to go back for the weight loss results but the side effects and the bleeding zombie feeling are too severe. I wish I could take it tho.


I have been on phentermine for a little over a month now and I’m on the depo shot. I don’t get my period because I am on the shot (and I still haven’t gotten it), but now I bleed during sex?


Haven’t had period since uterine ablation in 2011. Been on adipex a week today and have bleeding and period cramps??


I am in my 3rd month of taking phentermine. I have lost 15 lbs which is great, but the 1st month and the 3rd month I have started spotting a week before my period is due and end up having a 10 day period. I am on an oral birth control pill that has always made my periods regular always starting in day 23 and done by day 28. I’m definitely not a fan of the early spotting and feeling like I’m having my period every 2 weeks while on the pill.


Back to All Phentermine Side Effects

  1. Members of “Losing Weight with Phentermine” Support Group on Facebook & Forum. (2019, March 13). [User Report of Common Phentermine Side Effects]. Unpublished raw data.
  2. Hormone Health Network. (n.d.). What does estrogen do? [Brochure]. Author.
  3. Stress and Your Menstrual Period: A Cycle That You Can Break. (2010, February 17).
  4. Mady, M. A., Kossoff, E. H., Mcgregor, A. L., Wheless, J. W., Pyzik, P. L., & Freeman, J. M. (2003). The Ketogenic Diet: Adolescents Can Do It, Too. Epilepsia, 44(6), 847-851. doi:10.1046/j.1528-1157.2003.57002.x
  5. Physicians Committee for Responsible Medicine. (2019). Using Foods Against Menstrual Pain.
  6. Barnard, N., Scialli, A., Hurlock, D., & Bertron, P. (2000). Diet and sex-hormone binding globulin, dysmenorrhea, and premenstrual symptoms. Obstetrics & Gynecology, 95(2), 245-250. doi:10.1016/s0029-7844(99)00525-6
  7. The Royal Women’s Hospital. (n.d.). Exercise, diet & periods.
  8. American College of Obstetricians and Gynecologists. (2015, May). Premenstrual Syndrome (PMS).
  9. Healthwise Staff. (2018, September 5). Birth Control: Pros and Cons of Hormonal Methods (S. Marshall, A. Husney, K. Romito, & R. Uranga, Eds.).
  10. Mayo Clinic Staff. (2018, December 04). Hypothyroidism (underactive thyroid).
  11. NHS. (2019, February 01). Polycystic ovary syndrome.