Do contraceptive pills change your behaviour?

What does the contraceptive pill do?

Most of us know that our hormones play a part in how we are feeling and how our mood changes. Those of us who have used the birth control (contraceptive) pill will also be aware that our sex hormones control the female monthly (menstrual) cycle and therefore our ability to become pregnant.

We take the contraceptive pill, which changes the balance of these hormones, for a targeted purpose (usually to prevent pregnancy). However, many of us are less aware that the outcome in our bodies isn't targeted. This is because our sex hormones, oestrogen and progesterone, influence so much more than our fertility.

Hormones are chemical messengers in our bodies that travel through our blood to specific receptors. These 'messages' control the way our organs and systems work. This includes the brain, the organ that controls our emotions, behaviours, and many other things that make us who we are.

"Our sex hormones are a key part of the signalling machinery that makes us, us," explains Dr Sarah E. Hill, evolutionary psychologist and author of This is Your Brain on Birth Control.

"They affect pretty much everything - including mood, learning and memory, motivational states, who we are attracted to, how sensitive we are to sights and sounds, our metabolism, how effectively we exercise, the activities of our immune system, the activities of our circulatory system, and the structure and function of the brain. Our hormones aren’t something that happen to us. We are our hormones."

How do contraceptive pills work?

Hormonal contraceptive pills are a safe and reliable method of contraception. For sexually active women wishing to prevent pregnancy, they can provide significant social, cultural, and economic freedom. The contraceptive pill can also help to ease painful and heavy periods, and improve acne; it may even reduce the chances of ovarian and cervical cancer.

Types of contraceptive pills

What are the side effects of contraceptive pills?

Beyond these benefits, it's important to know the potential side effects of the contraceptive pill. This includes physical side effects such as breakthrough bleeding, and the more serious links (for COCs) with blood clots - causing deep vein thrombosis and pulmonary embolism (although alterations to the pill in recent decades have made these uncommon).

In women with additional risk factors for stroke - such as smoking, high blood pressure or migraine (especially with aura) - the risk of stroke is increased by taking the COC, which is why these contraceptive pills are not recommended in women at high risk.

There are also psychological side effects of birth control pills. While many people have a wholly positive experience, some people report low moods and poor mental health. Some experts also believe that the contraceptive pill influences our behaviour and life choices.

"Changing our hormones changes what our brains do. This means that the version of ourselves that we are when we are on hormonal contraceptive pills is a different version of ourselves than we are when we are off them," says Hill.

The contraceptive pill and mental health

According to Dr Ali Abbara, senior clinical lecturer in endocrinology at Imperial College London: "Some people are more sensitive to mood changes than others."

"It's also important to note that for women who have severe PMS or PMDD, the hormone-suppressing effects of hormonal contraceptive pills can be therapeutic and improve mood," Hill adds.

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Does the contraceptive pill cause mood swings?

Research reflects that people react differently. One study of a low-dose COC found it to have no impact on mood, while another study based on women with a previous history of COC-induced negative mood reported mood swings and depressive mood. In contrast, an analysis of four studies involving 50,000 women showed that the contraceptive pill could in fact reduce anxiety and mood swings.

It is difficult for experts to compare and summarise the effects on mood as studies use different instruments for assessment. They also analyse different types of contraceptive pills that contain different forms and strengths of oestrogen and progestogen.

Nevertheless, scientists generally agree that mood swings are relatively common but advise that external events are often a major influence. Mood swings include both positive and negative emotions, driven by a "small but statistically significant" group of women who suffer from COC-related side effects.

Can the contraceptive pill cause depression and suicide?

There is less evidence that the contraceptive pill can directly cause clinical depression. While links have been found, other influential factors such as personal history of poor mental health make it hard to conclude the exact cause. This said, one important study of over 1.06 million women aged 15-34 years - with no prior diagnosis of depression - did identify an associated increase in the use of antidepressants and the first diagnosis of depression after taking contraceptive pills.

Some data also suspect that taking the contraceptive pill may increase the risk of a suicide attempt. However, it is important to point out that it's not conclusive that the contraceptive pill is the direct cause. In addition, in real terms, the increase is very small - in one study, women who were taking oral contraceptive pills were about twice as likely to take their own lives, but the overall figures were 71 suicides out of almost half a million women studied.

The contraceptive pill and life choices

You may be surprised to learn that the psychological effects of birth control pills may also be influencing your life choices:

"The decisions that we make when we are naturally cycling aren't always the same decisions we would make when under the influence of the contraceptive pill (and vice versa). This can have implications for elements such as women's job satisfaction, relationship satisfaction, and the divorce rate," says Hill.

Does birth control make you lose interest in your partner?

"Research finds that women who choose their partners when they are on hormonal contraceptive pills have less sexual satisfaction," Hill explains. "However, they are less likely to get divorced.

"This may be because women on the contraceptive pill are thought to be less tuned in to a partner's "sexiness" and more tuned in to cues associated with long-term pair-bonding, such as resource access and intelligence."

This happens because the contraceptive pill balances out a woman's level of oestrogen and progesterone, mimicking the hormonal state of pregnancy. During this state, women are naturally more drawn to individuals who are likely to support child-rearing.

It may be hard to believe that altering our sex hormones can have such a tangible influence on our relationships. However, it is well documented by evolutionary scientists that both women and men are naturally influenced by the female menstrual cycle when it comes to choosing a romantic partner. In other words, our sex hormones have always played a key role in our relationships.

Can contraceptive pills cause hormonal imbalance?

The contraceptive pill is a highly reliable method of birth control. It's important to remember that for a large number of people the contraceptive pill works without any adverse side effects. At the same time, it's worth understanding that the hormones in the contraceptive pill may affect our behaviour - even if the outcome isn't negative.

"We need to take the time to educate ourselves about our sex hormones and the effects of the contraceptive pill," advises Hill. "I wrote This Is Your Brain On Birth Control to help women understand these issues in an easy-to-read, understandable way."

What's more, if you believe your contraceptive pill may be causing you to feel low, or experience depression and anxiety, Abbara recommends trying a different formulation containing an alternative progestogen:

"The effect on mood does appear to be related to the progestogen component, and so it may be a case of finding the right fit for the right person."

For example, the brand called Yasmin contains drospirenone, a progestogen that has shown some promise in reducing mood-related symptoms of severe premenstrual syndrome (PMS). Your GP will be able to discuss the various options with you.

Remember, birth control tablets - and other hormone-altering contraceptives - are also not the only methods to prevent pregnancy. You may decide that non-hormonal contraception is right for you.