Birth control pills, a common form of contraception, have two types: combination pills containing both estrogen and progestin, and progestin-only pills often referred to as "mini-pills". In both types, the active ingredients are synthetic hormones that mimic the natural ones in our bodies, but what exactly are these synthetic hormones made of, and how do they work to prevent pregnancy?

To understand the composition of birth control pills, let's dive into the world of synthetic hormones, their mechanisms, and the inactive ingredients that make up these small, accessible, and effective contraceptive options.

Active Ingredients: Synthetic Hormones
The active ingredients in birth control pills are synthetic hormones that work by mimicking the natural ones produced by our bodies. The most common hormones used in birth control pills are synthetic estrogens and progestins, which are modifications of the naturally occurring estrogens (like estradiol) and progestogens (like progesterone).

These synthetic hormones are created in laboratories using processes similar to those used in manufacturing pharmaceuticals. The synthetic estrogen most commonly used in birth control pills is ethinylestradiol, a modified form of estradiol. Progestins used in birth control pills are synthetic versions of the naturally occurring progesterone, with common examples including levonorgestrel, norethindrone, and drospirenone.
Synthetic Estrogens

Ethinylestradiol, the most common synthetic estrogen used in birth control pills, is an esterified alcohol with the molecular formula C21H28O2. It is primarily produced from the Extraction and chemical modification of natural estradiol derived from horse urine. Ethinylestradiol is used as a potent estrogenic component in combination pills.
In birth control pills, ethinylestradiol works by blocking the release of the luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which prevents the mid-cycle surge of LH that triggers ovulation. This hormonal manipulation is how synthetic estrogens help prevent pregnancy in combination pills.
Synthetic Progestins

Synthetic progestins used in birth control pills vary in structure and function, but they all share the ability to mimic the natural progestogen, progesterone. Some common synthetic progestins include levonorgestrel, norethindrone, and drospirenone, each with unique chemical structures and mechanisms of action.
Levonorgestrel, for example, is an 18-methyl derivatives of progesterone with the molecular formula C21H28O2. It works by thickening the cervical mucus, making it difficult for sperm to move through the cervix and reach the egg. Additionally, levonorgestrel and other synthetic progestins can thin the uterine lining, making it less hospitable for a fertilized egg to implant.
Inactive Ingredients in Birth Control Pills

Birth control pills also contain inactive ingredients, or excipients, which act as fillers, binders, and stabilizers to ensure the pills maintain their size, shape, and consistency. These inactive ingredients also help with disintegrating the pill quickly once swallowed. Common inactive ingredients in birth control pills include:
- Lactose, used as a diluent or filler, which is typically sourced from milk and is an ideal option because it's inexpensive and harmless to most users.
- Maize starch, an essential ingredient that acts as a binder, helping to form the pill into its final shape and structure.
- Hypromellose, a derivative of cellulose used as a film-coating agent to give birth control pills their characteristic shake and shiny appearance.








While these inactive ingredients play a crucial role in the production and usability of birth control pills, they are generally considered safe and pose no threat to users when administered correctly.
How Birth Control Pills Work Together
In combination pills, synthetic estrogens and progestins work together to create an artificial hormonal environment that suppresses natural hormone fluctuations, preventing ovulation, thickening cervical mucus, and thinning the uterine lining. This hormonal manipulation inhibits pregnancy by making it virtually impossible for sperm to fertilize an egg.
In progestin-only pills, the synthetic progestin works alone to create similar hormonal changes, mainly by thickening cervical mucus and thinning the uterine lining. These mechanical changes make it challenging for sperm to reach the egg and for a fertilized egg to implant in the uterus.
As we've explored the synthetic hormones and inactive ingredients making up birth control pills, it's clear that these small, accessible contraceptive options are a result of sophisticated medical research and pharmaceutical manufacturing processes. With ongoing advancements in hormonal contraception, the future of birth control pills looks promising, with continued efforts to improve their effectiveness, safety, and accessibility.