In this article: 

• Types of oral hormonal birth control

• How it affects the thyroid

• Oral birth control and thyroid hormone medication absorption

• Link between oral contraception and fertility

Thyroid hormones work closely together with male and female sex hormones. Estrogen and progesterone are the two primary female sex hormones that regulate the female reproductive cycle. Women who take synthetic (human-made) forms of estrogen and progesterone can experience specific side effects other than pregnancy prevention and correcting hormonal imbalance. If you are interested in using oral contraception or "the pill," it is essential to understand how it can affect your thyroid health.

Types of oral birth control pills

There are many types of birth control available, including hormonal options like IUDs, oral contraceptives, shots, the skin patch, or vaginal ring, and non-hormonal methods like condoms, diaphragms, sponges, or natural family planning.

Ahead, we focus on the different types of oral contraceptive pills. 

You and your doctor will choose the best oral contraceptive pill (OCP) based on what you intend to use it for and your medical history. Hormonal birth control is prescribed for: 

• Pregnancy prevention

• Irregular periods

• Severe cramping

• Acne

• Premenstrual syndrome (PMS) and perimenopausal symptom relief

• Polycystic ovarian syndrome

• Anemia

• Ovarian cysts

• Endometriosis

• Menstrual migraine relief

Some types of OCP may also reduce your risk for certain cancers, including ovarian cancer.

There are several different oral hormonal birth control options available to women. Talk to your health care provider to help decide which type is right for you and your partner based on your medical history, menstrual symptoms, medications, and whether or not you are breastfeeding.

Combination pills

This category of birth control pill contains both synthetic estrogen and progestin. These pills work in two ways: they prevent ovulation and thicken the cervical mucus to prevent sperm from entering the uterus. There are different types of combination pills with varying hormone levels and directions for use:

Monophasic pills

These pills follow a 28-day cycle. Three weeks of active pills contain the same dose of hormone followed by one week of inactive pills that you take the week you start your menstrual period.

Multiphasic pills

Also taken in 28-day cycles, these pills have varying hormone levels throughout your period cycle that aim to mimic your natural hormone fluctuations. Like monophasic pills, the last week contains inactive pills.

Extended-cycle pills

These pills often follow 13-week cycles, where you take active pills for 12 weeks and take inactive pills for the 13th week. Extended-cycle pills make you only have a period 3-4 times annually.

Progestin-only pills

Also called the minipill, this type of OCP does not have estrogen and thus only contains progestin. These pills work by thickening the cervical mucus, thinning your uterus' lining, and possibly preventing ovulation. Women who are breastfeeding or who cannot take estrogen for health reasons can use progestin-only pills. There are no inactive pills, so some women may not have a period while taking these pills.

How oral contraceptives affect the thyroid

Some studies have found that OCP's have minor effects on thyroid function. Researchers found participants had elevated T3, T4, and cortisol levels with use in a study of four different monophasic pills. 

Estrogen also causes an increase in thyroxine-binding globulin (TBG) levels. TBG is a liver protein that is responsible for moving thyroid hormones through your circulatory system. When you have an increase in TBG, your available free thyroid hormone decreases. Therefore, you may need to adjust your thyroid hormone replacement medication. 

Research also suggests that OCP's can cause nutritional deficiencies because they interfere with your ability to absorb nutrients from food. The thyroid requires specific vitamins and minerals to make thyroxine (T4). Zinc, selenium, and magnesium play an essential role in overall thyroid function. OCP's decrease the absorption of these minerals, along with folic acid, and vitamins B2, B6, B12, C, E. Because our cooking and storage methods often deplete our food of nutrients, taking supplements may help reverse nutritional deficiencies caused by OCP's.  

Women with subclinical hypothyroidism are also at higher risk for cardiovascular events such as blood clots while taking OCP's. Hypothyroidism is associated with a higher amount of platelets in the blood compared to those that are euthyroid. 

Oral birth control and thyroid hormone medication absorption

Thyroid hormone replacement medication, such as levothyroxine, should be taken on an empty stomach to maximize absorption. It is best to take this medication 30-60 minutes before taking any other drugs or eating or drinking. This window of time allows your gut to absorb and circulate the synthetic hormone before other medicines and foods can interfere. 

If you are taking OCP's, the same rules apply: take your thyroid hormone medication separately from your birth control pill. This instruction is especially relevant for women using OCP's with estrogen as this hormone increases your need for synthetic thyroid hormone. Always take your medication as prescribed by your doctor.

If you start an OCP, your doctor will likely want to re-test your thyroid function a few weeks after you begin to ensure you are getting an adequate dose of thyroid hormone. 

THYROID GUIDE

Your Guide To Thyroid Medication

Optimizing your thyroid levels with thyroid hormone replacement medication is usually the first step in minimizing symptoms.

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Link between oral contraceptives and fertility

There may be some concern that taking an oral contraceptive pill may hurt your ability to one day conceive. Research indicates that this is likely not the case. Long-term use of OCP's should not affect a woman's chances of becoming pregnant.

A study published in the Journal Human Reproduction suggests that the fertility of both short- and long-term users of OCPs may be slightly reduced during the first few menstrual cycles after stopping use. After that, however, monthly fertility rates are comparable to those of people who stop other birth control methods. 

Another study published in the Reviews Obstetrics and Gynecology tracked nearly 60,000 users of oral contraceptives to determine their chances of conceiving after discontinuation. About 20% achieved a pregnancy in their first cycle after stopping use and 80% within the first year after discontinuation, no matter the type of oral contraceptive used.

A note from Paloma Health

For oral contraceptives to work best, you should follow your doctor's instructions or the package, exactly. Talk with your health care provider to assess your thyroid function and decide if birth control pills are a good option for you.

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