Birth control and weight gain, explained 

Unwanted weight changes, especially weight gain, are up there as some of the top reasons people with cycles stop or switch birth control pills (1).

But, a bit like birth control and mental health, the research on the relationship between weight change and birth control pills is not completely clean-cut (2). 

There are a myriad of factors that can cause weight change, from our biological baselines to bloating—but a seriously overlooked influencer (as always) is our hormones (3). 

Changes in our female sex hormone levels—whether that be during our monthly menstrual cycles,  throughout our lives, or from using hormonal birth control—can all cause weight change (the ups and the downs). 

So how exactly do our hormones impact our weight? And how do we decipher if it’s our birth control pill that’s making us gain weight? Let’s take 5, and find out...

The menstrual cycle and weight change

Many monthly menstruators report feeling heavier, or literally weighing more, just before our periods start. 

Fact check—it’s actually totally normal to put on anything between 2 and 6 pounds during our periods. This additional weight gain we then shed in the days after our bleeding stops (4).

But where do these extra pounds come from?

Fluid retention

Throughout our menstrual cycles, just before our periods start, estrogen and progesterone both take a dip, which acts as a signal to the uterus that, honey, it’s shred time. 

Estrogen and progesterone also control how our bodies regulate fluid (5). When both dip out before our bleed, our tissues hold onto more water—causing what’s known as water retention or edema (4). 

This is completely normal but can cause swelling, puffiness and plumping in our boobs, stomach, face and even extremities (don’t worry you shouldn’t have to go up a shoe size). 

Although an increase in fluid adds to our weight, this is not fat gain.

Bloating and gut issues

Bloating is another super common PMS symptom, which although doesn’t actually cause weight gain, makes us feel sluggish, frumpy and grumpy. 

Water retention and gastrointestinal changes (think period poop) can cause period bloat (6,7). 

Progesterone also reduces intestinal muscle contractions which can cause slow digestion, which is why in the week before our periods when our progesterone is high, it’s common to feel a bit blocked up or even suffer from some constipation (6) 

Neither period bloating or constipation actually cause weight gain, but both can be uncomfortable and add to that general feeling of heaviness.

Cycle cravings

Changes in our hormone levels throughout our cycles can also cause big changes to our fancy for food. 

When progesterone rises in the latter half of our cycles, so does our appetite. This is because progesterone is an appetite stimulant, enticing us to bulk up before our bleeds. 

Increased appetite is also affected by low estrogen levels just before our periods. Estrogen regulates our levels of serotonin, our mood-controlling neurotransmitter. Low estrogen also means low serotonin—and because sugar helps the body create more serotonin, our brains turn on the carb-heavy cravings. 

Dehydration

Our insatiable appetite for sugar doesn’t stop there. Magnesium is a mineral involved in regulating our hydration levels (8). During our periods, our magnesium levels drop, meaning we’re more likely to feel dehydrated and crave sweet treats.

All in all, our bodies are doing just about everything they can to make us eat more during the week leading up to and during our periods. Although this is completely normal, it’s so easy to feel guilty on part of our hungry hormones (not to mention the ridiculously unrealistic societal pressures for us to maintain ‘the perfect weight’). 

Make sure you are taking care of yourself (including mentally), and try not to worry about weight changes during this time in your cycle. You’re likely to feel right back on track (once your estrogen is rising and dampening your appetite again) just after your bleed.

Hormonal birth control and weight change 

Hormonal birth control contains synthetic ((wo) man-made) versions of our naturally occurring female sex hormones. Synthetic hormones cause the same bodily changes as our natural hormones, and so may cause all the same effects as the ones we’ve just covered—potentially resulting in weight changes. 

Fluid retention is a really common side effect of hormonal birth control, especially those containing estrogen (1)—whereas progesterone-only methods may lead to increases in appetite because they keep our progesterone levels at a constantly high, pre-period level (9). 

Although (silver linings) both of these side-effects are better with more modern methods because they tend to lower doses of hormones than the old school versions (10). 

Some birth control pills can also disrupt our levels of androgens, like testosterone—higher androgens often cause increases in appetite, whilst lower levels reduce our cravings (9). 

Finding the right fit for you

Weight change and hormonal birth control, or even just our hormones in general, can feel like a really tricky place to navigate. 

The research might be murky, but this is often because it focuses on averages, rather than individuals—and that’s not the Tuune way of doing things. 

We know you’re anything but average—irresistibly individual in fact. No matter what your thoughts or goals for your weight are, we can help you to find the right birth control for you based on your biology. 

Essentially, to take the guesswork and trial and error out from your relationship with birth control. 

It’s a common myth that all changes in body weight are linked to changes in our fat levels—but as we’ve seen, there are many other factors at play. 

But, if you’re concerned about changes in your weight due to hormonal birth control—remember, we’re here to help.

Written by

Annalisa Hayes (she/her)

Copywriter at Tuune, Annalisa has worked for various pioneering health-tech startups and healthcare companies with purpose-led missions. Driven by empowering people to take control of their health, she helps make the science behind hormones accessible for our community, so they can make clued-up choices about their healthcare.

Medically reviewed by

Dr. Arushee Prasad, GP, MBBS (she/her)

Dr Arushee Prasad is a GP for NHS England with an MBBS in Medicine and Surgery, and an MRCGP from the Royal College of General Practitioners. Passionate about digital health and algorithmic medicine, Arushee was previously an Algorithmic Medical Doctor for Docly.

Scientifically researched by

Hannah Durrant (she/her)

Hannah is a Biomedical Content Writer at Tuune, with a BSc in Biomedical Sciences from University College London. She is passionate about bringing together the scientific community and the general public by disseminating modern science via digestible, engaging and thought-provoking content.