Breakthrough bleeding is unwanted or unplanned spotting or bleeding while using the birth control pill, injection, rings, patches or implants, or hormone therapy. Breakthrough bleeding when using hormones can be inconvenient and annoying, but is common and not thought to be dangerous.

Why does breakthrough bleeding occur?

Breakthrough bleeding can be triggered by a few different things. Maybe you have just started on hormone therapy, or a contraceptive ring or pill, stopped using hormonal birth control, forgot to put your Nuvaring in, skipped a pill, ran your rings/pill packets together, or switched pill types.

If none of these applies to you, then it’s possible that your bleeding is due to another cause, and you should be checked. See our information on bleeding between periods for more.

There are four specific causes of breakthrough bleeding:

  1. The effect of the ring/pill hormones on your endometrial lining
  2. The dose, formulation and regime of hormones that you are on
  3. Your habits and behaviour when taking the pill (skipping, other medication, smoking, etc.) or using hormones
  4. Another condition that is unrelated to your birth control or hormone therapy

Understanding how your endometrium works

Your endometrium is the layer of cells that make up the lining of your uterus and what ends up as your period/bleeding. During the build-up to your period, these special cells grow more numerous, with abundant blood vessels tangled within.

You get your period because the blood vessel tips in the endometrium get constricted by hormonal signals, and your period is the endometrial tissue dying and falling off. This is like tying a rubber band around your finger, cutting off the blood supply. If you left the rubber band there, your finger would eventually fall off.

No blood supply means the cells simply fall off the wall of your uterus like old skin cells.

Your endometrium isn’t involved in the contraceptive element of the pill, but it is affected by the hormones nonetheless. The response of your endometrium to the pill is predictable, and means we can figure out the patterns that will predictably occur.

This is how we know that when you stop taking the pill for seven days on your sugar pill days that you will get what’s known as withdrawal bleeding – or a period brought on not by natural hormones being withdrawn, but from synthetic hormone withdrawal. This causes the same rubber band effect on the endometrial cells, causing them to slough off as a period.

The effect of oestrogen and progesterone on your endometrium

Oestrogen causes the endometrium to grow, while progesterone tells it when to pause and stay stable. This means in the pill the mixture of oestrogen and progesterone builds up the endometrial lining, then keeps it steady until you stop taking the pills, at which time the lining sheds, as your ‘period’.

This is what sort of happens in a natural cycle. When you get your period, it means both oestrogen and progesterone have dropped off significantly, leaving you with the rubberband effect. Then, it starts all over again.

Right after your period the lining starts building up again, then after you ovulate, progesterone kicks in to keep your lining thick and steady in case you get pregnant. This lining feeds the embryo in its very early stages.

How the birth control pill affects your endometrium

The pill comes in a few different forms, but the most common is what’s known as the combined pill containing synthetic progesterone (progestin) and oestrogen. These synthetic hormones have a huge effect on the endometrium.

The progestin component of contraceptive pills is generally responsible for the ovulation-blocking effect, so the oestrogen component can be increased or decreased. The latest pills aim to use the least hormone necessary to prevent ovulation, which tends to mean less oestrogen (less than 50 μg). Less oestrogen means a less stable, strong and abundant endometrial lining, and breakthrough bleeding can occur randomly.

Progestin can also contribute to breakthrough bleeding, but the type of progestin in the pill seems to matter more than anything else.

Oestrogen-progestin balance seems to be more important than just the level of oestrogen when it comes to breakthrough bleeding. The delicate balance of the endometrium still remains a bit of a mystery – there are theories, but no concrete answers.

Hormones and dosage and how this affects breakthrough bleeding

There are dozens of contraceptive pills available globally, with each containing its own patented blend of oestrogen and progestins. Each brand is slightly molecularly different to the others, because this is required for patents. This is why if one pill doesn’t go down very well in your body, it pays to try a few to see which works best for you, if any.

The pills that contain the lowest doses of oestrogen (≤20 μg) are associated with the most breakthrough bleeding, but low doses of either oestrogen or progestin can increase breakthrough bleeding. Breakthrough bleeding also tends to decrease the longer a woman has been taking the pills.

Biphasic, triphasic, extended-cycle or continuous use pills and breakthrough bleeding

Women on extended cycle birth control pills may see more breakthrough bleeding than those on a 28-day cycle pill. Biphasic means running two pill packets together, while triphasic means running three pill packets together, leaving just 7 planned bleeding days. In a 28-day cycle, there are 21 days of planned bleeding in the three-monthly cycle. In continuous use pills, all bleeding is considered breakthrough bleeding.

Factors that contribute to breakthrough bleeding

Skipping doses of your hormone doses is incredibly common, and a major cause of breakthrough bleeding. When electronically monitored, it was found that over 80 per cent of women on the pill missed at least one pill, with at least half skipping three or more per cycle. Taking the pill at the same time every day can also help.

Women who experience nausea were more likely to skip pills and stop taking them altogether. Additionally, women taking over-the-counter supplements or medications saw some interference in the activity of the pill, for example supplements that improve liver function can cause hormone clearance quickly, leading to breakthrough bleeding. St John’s wort is a common contributor to breakthrough bleeding and possibly ovulation.

Smoking has been associated with anti-oestrogenic effects, however the exact mechanism of this is not known. Smoking may lower oestrogen levels and cause breakthrough bleeding even in good pill-takers. Women who smoke a lot are more at risk of breakthrough bleeding than those who smoke occasionally or less.

Non-pill-related causes of breakthrough bleeding

      What to do if breakthrough bleeding is a problem on the pill

You can try a different pill, go off the pill and try another contraception, or adjust your dosing regime.

Jessica Lloyd - Naturopathic Practitioner, BHSc(N)

Jessica Lloyd - Naturopathic Practitioner, BHSc(N)

Jessica is a degree-qualified naturopath (BHSc) specialising in vulvovaginal health and disease, based in Melbourne, Australia.

Jessica is the owner and lead naturopath of My Vagina, and is a member of the:

  • International Society for the Study of Vulvovaginal Disease (ISSVD)
  • International Society for the Study of Women's Sexual Health (ISSWSH)
  • National Vulvodynia Association (NVA) Australia
  • New Zealand Vulvovaginal Society (ANZVS)
  • Australian Traditional Medicine Society (ATMS)
Read more about Jessica and My Vagina's origin story.