Slynd is a progestin-only birth control pill. Each pack contains 24 white active tablets, each with 4 mg of drospirenone, and 4 green placebo tablets that contain no active ingredient. Unlike most combination birth control pills, Slynd contains no estrogen, which makes it an option for people who can’t tolerate or shouldn’t take estrogen-based contraceptives.
The Active Ingredient: Drospirenone
Drospirenone is a synthetic progestin, meaning it mimics the hormone progesterone that your body naturally produces. At 4 mg per tablet, Slynd’s dose is higher than the drospirenone found in some combination pills (which typically use 3 mg alongside estrogen). That higher dose is intentional: without estrogen to help, drospirenone needs to do the heavy lifting on its own.
Drospirenone prevents pregnancy primarily by suppressing ovulation, stopping your ovaries from releasing an egg each cycle. This sets Slynd apart from older progestin-only pills (sometimes called “mini-pills”), which relied more on thickening cervical mucus and were less consistent at blocking ovulation. Because Slynd reliably suppresses ovulation, it also comes with a more forgiving missed-pill window. You have up to 24 hours to take a late pill before protection is compromised, compared to just 3 hours with traditional mini-pills.
One notable property of drospirenone is that it has mild anti-mineralocorticoid activity. In practical terms, this means it can raise potassium levels in your blood. For most people this isn’t a concern, but it matters if you have kidney problems, adrenal insufficiency, or take other medications that also raise potassium.
Inactive Ingredients in the White Tablets
Beyond the 4 mg of drospirenone, each white active tablet contains several inactive ingredients (excipients) that give the pill its structure, help it dissolve properly, and create its coating:
- Tablet core: microcrystalline cellulose, lactose, colloidal anhydrous silica, magnesium stearate
- Tablet coating: poly(vinyl alcohol), titanium dioxide (the white color), macrogol, talc
The lactose content is worth noting if you have a severe lactose intolerance or allergy. The amount in a single pill is very small, but it is present in both the active and placebo tablets.
What’s in the Green Placebo Tablets
The four green pills at the end of each pack contain no drospirenone or any other active drug. They exist to keep you in the habit of taking a pill every day. Their ingredients are purely structural and cosmetic:
- Tablet core: lactose monohydrate, maize starch, povidone, colloidal anhydrous silica, magnesium stearate
- Tablet coating: hypromellose, triacetin, polysorbate 80, titanium dioxide, indigo carmine aluminum lake (the blue-green pigment), yellow iron oxide
The green color comes from the combination of indigo carmine (a blue dye) and yellow iron oxide. If you skip the green pills entirely, it won’t affect your contraceptive protection, though you’ll need to start your next pack on time.
The 24/4 Dosing Schedule
Slynd uses a 24-day active, 4-day placebo cycle. This is different from the classic 21/7 schedule used by many combination pills. The shorter hormone-free interval helps maintain ovulation suppression more reliably. During the four placebo days, you may experience a withdrawal bleed, though bleeding patterns on Slynd vary widely from person to person. Some people have lighter periods, irregular spotting, or no bleeding at all.
How Effective Slynd Is
In Slynd’s clinical trial, FDA reviewers calculated a Pearl Index of 4.0 among women 35 and younger. That translates to roughly 4 pregnancies per 100 women using Slynd over a year with typical use in the study. For context, this is broadly comparable to other oral contraceptives when accounting for real-world use, including missed pills and late doses. Perfect use would yield a lower pregnancy rate, but the clinical trial reflects conditions closer to how people actually take the pill.
Why Slynd Contains No Estrogen
Estrogen is the component in combination pills linked to increased risks of blood clots, and it can also worsen migraines with aura, raise blood pressure, and cause issues for people who are breastfeeding. By using only drospirenone, Slynd avoids those estrogen-related risks. This makes it a fit for people with a history of blood clots, certain types of migraines, or those in the postpartum period who are nursing. The tradeoff is that without estrogen, cycle control can be less predictable, and irregular bleeding is more common, especially in the first few months.