I have enough to give a comprehensive answer. Note: no single "medicine" is called a menstrual cycle regulator - the class depends on what's being regulated (irregular timing vs. heavy flow vs. delaying periods vs. PCOS anovulation).
Drugs Used to Regulate the Menstrual Cycle
There isn't one single "cycle regulation drug" - the choice depends on the underlying problem (irregular timing, absent periods, heavy bleeding, or PCOS-related anovulation). Here are the main categories used clinically:
1. Progestins (most common for cycle regulation)
- Medroxyprogesterone acetate (e.g., Provera) - 10 mg/day for 10 days causes a withdrawal bleed; used in women with chronic anovulation to induce a regular bleed at least 4 times a year and prevent endometrial hyperplasia - Textbook of Family Medicine, p. 617.
- Norethisterone (Regestrone, Primolut-N) - a progestin commonly used to regulate irregular cycles or temporarily delay/postpone menstruation.
- Depot medroxyprogesterone acetate (Depo-Provera) or a levonorgestrel IUD - for longer-term cycle/bleeding control when contraception is also desired - Berek & Novak's Gynecology; Textbook of Family Medicine.
2. Combined Oral Contraceptives (COCs)
Estrogen-progestin pills impose an artificial, predictable cycle and are frequently used both to regularize irregular menses and to reduce heavy flow - Berek & Novak's Gynecology, p. 3625; Swanson's Family Medicine Review, p. 2964. High-dose OCs (up to 4 pills/day for 5-7 days) are also used acutely to stop abnormal uterine bleeding episodes.
3. Drugs for PCOS-related irregularity (anovulation)
- Metformin - improves insulin sensitivity and can restore ovulatory cycles in PCOS.
- Spironolactone - an anti-androgen shown to help regularize cycles in adolescents with PCOS.
- Clomiphene citrate - used for ovulation induction when pregnancy is desired, not just cycle regularity - Berek & Novak's Gynecology, p. 3398; Textbook of Family Medicine, p. 1682.
- Flutamide - anti-androgen, used in some PCOS cases with hirsutism.
4. Other bleeding-related agents (not true "regulators" but often confused with them)
- Tranexamic acid and NSAIDs (e.g., mefenamic acid) - reduce heavy menstrual flow (menorrhagia) without changing cycle timing.
- Bromocriptine/cabergoline - for irregular/absent cycles caused by high prolactin (hyperprolactinemia).
- Danazol / GnRH agonists - used for heavy bleeding or fibroid-related bleeding, but they suppress cycles temporarily rather than "regulate" them.
Key point on choice of drug
- Want a regular, predictable bleed without pregnancy risk: COCs or cyclic progestin.
- Trying to conceive with irregular ovulation (e.g., PCOS): clomiphene citrate ± metformin.
- Heavy but regularly timed periods: tranexamic acid or NSAIDs, not a hormonal "regulator."
- High prolactin causing irregular cycles: bromocriptine/cabergoline after confirming the diagnosis.
All of these require an actual diagnosis first (thyroid disease, PCOS, hyperprolactinemia, structural causes, or pregnancy must be ruled out), since the "irregular cycle" symptom has very different underlying causes that call for different drugs - Textbook of Family Medicine, p. 617.
This is not a substitute for a gynecologist's evaluation. Self-medicating to "regulate" periods without knowing the cause can mask underlying conditions (thyroid disease, PCOS, hyperprolactinemia, endometrial pathology, or pregnancy). A clinician should confirm the cause via history, exam, and basic labs (TSH, prolactin, pregnancy test, pelvic ultrasound as indicated) before starting any of these.