The oral contraceptive pill literally changed the world. It allowed women to take control of their own reproductive choices - a change that led to a cultural revolution.

But something that is designed to disrupt the body's hormones won't work the same for all women, and may not work at all for some.

In fact, according to Deborah Bateson, a practising doctor, gynaecologist, and Medical Director of Family Planning New South Wales, it may even change over time for a single patient.

"There isn't an ideal form of contraception for an individual woman at different stages of her reproductive life," she told ScienceAlert. "What suits her when she's 18 may perhaps be very different from when she's in her 20s, or after she has a child - if she has a child - or when she's approaching menopause."

Want to start taking the pill? Taking the pill and want to know more about it? Here's some information you can take to your doctor - as advised by another doctor.

How it works

Over the course of a menstrual cycle, the hormones fluctuate - oestrogen and progesterone start off relatively low during a woman's period. Then, over the course of the days leading up to ovulation, oestrogen levels rise, peaking when her ovary releases an egg into the uterus.

Once the egg has been released, the egg follicle transforms into a corpus luteum, which releases progesterone; and, following ovulation, oestrogen falls before rising again slightly.

Both hormones help the uterine lining to thicken. If the egg remains unfertilised, the corpus luteum stops producing progesterone, oestrogen levels fall again, and the uterine lining is shed in another menstrual period.

A drop in oestrogen usually tells the hypothalamus to produce hormones that trigger a follicle to mature and release an egg in ovulation.

Fascinating, huh? What the combined oral contraceptive does is maintain steady levels of oestrogen and progesterone, which simultaneously prevents ovulation by neutralising its hormone triggers, and thickens the cervical mucus so that, even if an egg is released, sperm can't get to it. Clever!

But it does some other stuff, too. And that's where the experiences of individual people can vary.

The myths might not all be myths

There are many myths and misconceptions about the contraceptive pill and what some women have experienced as side effects.

One of the big ones is that the pill can cause weight gain, and while statistically there is no difference in weight gain in groups of women who are taking the pill and women who aren't taking the pill, the truth is that it may be more complicated than that.

"When we look at it in a population, there's no overall increase in a population of women taking the pill," Bateson explained, "but we know on an individual basis, some people may gain weight, some people may lose weight, and we need to listen to that."

There's no clear association, and women can certainly gain weight over time with or without the pill, but, Bateson says, if you are experiencing something on the pill that you weren't experiencing when you weren't taking it, you should go talk to your doctor.

The other big one is depression - and in fact studies have shown that the pill could be linked to low moods, with women in a double-blind study reporting a lower quality of life after taking the pill.

"But there's no causal association," she says. "We don't think going on the pill causes depression, but if someone was to develop mood swings, including depression, and they were taking the pill, we'd want them to come and see us."

There are actual legit health risks

The information sheet that comes with your pills will list side effects. Spot bleeding, nausea and sore breasts may go away as the body adjust to the new hormones. Others, such as headaches and lower libido, could go away if you change your pill.

However, there are actual health risks that can be associated with taking the pill, and therefore certain women should not be prescribed it at all.

"The main one for the pill is what we call deep vein thrombosis, and there is a slightly increased risk for women taking the pill," Bateson explained to ScienceAlert.

"The absolute risk for women is extremely low, but my job as a doctor is that I need to make sure that I don't prescribe the pill for … anyone with a higher than background risk of blood clots."

There's also an extremely low risk of stroke.

Background risks for blood clots and stroke include women who smoke, women with obesity, women with lupus, women over the age of 35, women with high blood pressure, and women who experience migraine with aura.

The frustrating thing is we don't know why that's the case.

We do know that, for some reason, the pill increases the blood's coagulability. Why does it do that? Complete mystery.

Still, according to Bateson, pharmaceutical companies are trying to develop pills that reduce the risk of blood clots, so that's something.

You can fall pregnant - but there's no danger to your foetus

Even when you use the pill exactly as it says on the box, it's not 100 percent effective. (There is no contraceptive available that has this sort of effectiveness rating.) With perfect use, though, it's not bad - 99.7 percent.

Of course, none of us are perfect. The 'real world' use for the pill is only 91 percent effective, which means 9 women in every 100 using the pill fall pregnant each year.

But thankfully, if you decide to continue with a surprise pill pregnancy, you don't need to worry.

"There's actually very good data out of Denmark .. where they were able to track women who'd carried on taking the pill, not realising they were pregnant, for a short period of time," Bateson explained.

"There wasn't any increase in what we call teratogenicity, or foetal malformations."

That also means that if you're looking to stop the pill to try to have a baby, you don't need to wait - you can start trying straight away.

There are other options available

If you don't want to or can't take the combined pill, there are other contraceptives you can ask your doctor about. These include (but aren't limited to) the IUD (either copper or hormonal), the contraceptive implant and the Depo Provera injection.

The most important thing, Bateson said, is to make sure you're informed of the pros and cons of each, and that you answer your doctor's questions as honestly as you can so they can make sure they're not providing you with a contraception that is a danger to you personally.

You can also read through online fact sheets for various options and try to narrow down which one you think might suit you best prior to your appointment.

"Some women find the pill that suits them straight away and that's great. And other women don't find the pill that suits them best, and it takes them quite a few goes to find something," Bateson said.

"Write down a list of questions before you see your doctor, that can be really helpful. It's not one size fits all."