Hormonal birth control can both promote and reduce hair growth, depending on its specific hormonal composition. Hormonal contraception uses synthetic versions of estrogen and progesterone to manipulate the body’s natural hormone levels and prevent pregnancy. Because hair follicles are highly sensitive to these hormonal shifts, the introduction of synthetic hormones can lead to noticeable changes in hair texture and growth patterns. The effect is individualized, determined by the balance of hormones in the contraceptive and a person’s unique sensitivity.
The Hormonal Mechanism Behind Hair Growth
Hair follicles are significantly influenced by hormones, particularly androgens, which are present in all women. The most potent androgen is dihydrotestosterone (DHT), converted from testosterone by the enzyme 5-alpha reductase. Androgens are the primary drivers for the growth of coarse, dark terminal hair in areas such as the face, chest, and back, a condition known as hirsutism.
When androgen levels are elevated or hair follicles are genetically hyper-sensitive, fine vellus hair can convert into thick terminal hair in these hormone-sensitive regions. Hormonal birth control works by changing the balance of circulating hormones, which alters the stimulation of hair follicles. Whether a contraceptive causes more hair growth or less depends entirely on how it affects the amount of active androgens available in the bloodstream.
Birth Control Types That May Increase Hair Growth
Certain hormonal contraceptives contain progestins that exhibit a higher “androgenic index,” meaning they mimic the effects of androgens like testosterone. These progestins can directly stimulate hair follicles or increase free testosterone, leading to unwanted hair growth (hirsutism) in susceptible individuals. This effect is commonly associated with progestin-only methods, such as the mini-pill, as they lack the counteracting effects of estrogen.
Hormone injections, such as Depo-Provera, and some hormonal implants are also known to have a higher androgenic potential. Older or higher-dose combination birth control pills containing progestins like levonorgestrel or norgestrel tend to have a higher androgenic index than newer formulations. Using one of these higher-androgen methods can exacerbate symptoms for those genetically predisposed to hair growth. The resulting hair growth is a side effect of the progestin acting on androgen receptors in the skin.
Birth Control Types Used to Treat Excessive Hair Growth
Conversely, combination birth control pills (containing both synthetic estrogen and progestin) are frequently prescribed to treat excessive hair growth (hirsutism). The estrogen component is responsible for this therapeutic effect, as it stimulates the liver to produce more Sex Hormone Binding Globulin (SHBG). SHBG binds to free testosterone in the bloodstream, reducing the amount of active androgen that can reach the hair follicles.
These anti-androgenic effects are maximized when the pill contains a low-androgenic progestin, which avoids counteracting the benefits of the estrogen. Progestins with low androgenic activity include desogestrel, norgestimate, and drospirenone. Drospirenone is particularly effective because it has its own anti-androgenic properties, directly blocking the effects of androgens at the receptor level. These formulations can significantly reduce unwanted terminal hair growth over several months of consistent use.
Managing Hair Changes and When to Consult a Doctor
If a person notices new or increased hair growth after starting a hormonal contraceptive, allow the body time to adjust to the new hormonal balance. Hair growth cycles are lengthy, so it can take three to six months for changes in growth patterns to stabilize. If the increased hair growth (hirsutism) persists or is a significant concern, consult a healthcare provider.
A doctor can evaluate the severity of the growth, often using a standardized tool like the Ferriman-Gallwey visual score. They will rule out underlying medical conditions that could be the true cause of the hair growth, such as Polycystic Ovary Syndrome (PCOS) or thyroid dysfunction. If the birth control method is identified as the likely cause, the doctor may recommend switching to a formulation with a lower androgenic index or one with anti-androgenic properties. Rapid, severe, or sudden onset of excessive hair growth, especially when accompanied by other symptoms like severe acne or a deepening voice, warrants a prompt medical evaluation.