A 19-year-old woman comes to the physician because of a delayed menstrual period. She has had regular menses since menarche at age 11. Her last menstrual period was 7 weeks ago. She is sexually active with two male partners. A urine pregnancy test is positive. An ultrasound of the pelvis shows a viable intrauterine pregnancy with an estimated gestational age of 6 weeks and 5 days. She does not wish to continue with the pregnancy. After carefully weighing the options with her physician, she is prescribed two medications, one of which is mifepristone. Which of the following is this drug's primary mechanism of action?

Blockage of progesterone receptor

Activation of prostaglandin E1 receptors

Inhibition of dihydrofolate reductase

Antagonist at gonadotropin-releasing hormone receptors

A 30-year-old woman presents to a medical clinic for a routine check-up. She gained about 5 kg (11 lb) since the last time she weighed herself 3 months ago. She also complains of constipation and sensitivity to cold. She also noticed her hair appears to be thinning. The patient started to use combined oral contraceptives a few months ago and she is compliant. On physical examination, the temperature is 37.0°C (98.6°F), the blood pressure is 110/70 mm Hg, the pulse is 65/min, and the respiratory rate is 14/min. The laboratory results are as follows: Thyroxine (T4), total 25 ug/dL Thyroxine (T4), free 0.8 ng/dL TSH 0.2 mU/L Which of the following is the main mechanism of action of the drug that caused her signs and symptoms?

Inhibition of hormones in the pituitary gland

Inhibition of an enzyme in the thyroid gland

Increase the thickness of cervical mucus secretions

Inhibition of hormones in hypothalamus

A 69-year-old woman comes to the clinic for an annual well exam. She reports no significant changes to her health except for an arm fracture 3 weeks ago while she was lifting some heavy bags. Her diabetes is well controlled with metformin. She reports some vaginal dryness that she manages with adequate lubrication. She denies any weight changes, fevers, chills, palpitations, nausea/vomiting, incontinence, or bowel changes. A dual-energy X-ray absorptiometry (DEXA) scan was done and demonstrated a T-score of -2.7. She was subsequently prescribed a selective estrogen receptor modulator, in addition to vitamin and weight-bearing exercises, for the management of her symptoms. What is the mechanism of action of the prescribed medication?

Estrogen antagonist in breast and agonist in bone

Estrogen antagonist in cervix and agonist in bone

Estrogen agonist in bone and breast

Partial estrogen agonist in endometrium and bone

Partial estrogen agonist in bone and antagonist in cervix

A 40-year-old man presents with a painless firm mass in the right breast. Examination shows retraction of the nipple and the skin is fixed to the underlying mass. The axillary nodes are palpable. Which of the following statements is FALSE regarding the above condition?

Lobular cancer is the most common breast cancer in males

BRCA2 mutations are associated with increased risk

These are positive for estrogen receptor

Endocrine therapy plays an important role in treatment

Gynecomastia may be caused by certain medications

A 21-year-old G2P1 woman presents to the clinic and is curious about contraception immediately after her baby is born. She is anxious about taking care of one child and does not believe that she can handle the responsibility of caring for another. She has no other questions or complaints today. Her past medical history consists of generalized anxiety disorder, antithrombin deficiency, and chronic deep vein thrombosis. She has been hospitalized for acute on chronic deep vein thrombosis. Her only medication is buspirone. Her blood pressure is 119/78 mm Hg and the heart rate is 78/min. BMI of the patient is 32 kg/m2. On physical examination, her fundal height is 21 cm from pubic symphysis. No ovarian masses are palpated during the bimanual examination. Ultrasound exhibits a monoamniotic, monochorionic fetus. Which of the following forms of contraception would be the most detrimental given her risk factors?

Transdermal contraceptive patch

Depot medroxyprogesterone acetate

Gonadal hormones (estrogens, progestins) for USMLE Step 2 CK: High-Yield Pharmacology Lessons

Estrogens - The Feminine Architects

Types: Estradiol (most potent), estrone, and estriol. Synthesized from androgens by aromatase.
Mechanism: Binds to nuclear estrogen receptors (ER-α, ER-β) to modulate gene transcription.
Key Effects:
- Promotes development of female secondary sexual characteristics.
- Stimulates endometrial proliferation.
- Maintains bone density by ↓ osteoclast activity.
- ↑ HDL & ↓ LDL; ↑ coagulation factors (risk of thrombosis).
Clinical Uses:
- Hormone replacement therapy (HRT) in menopause.
- Combined oral contraceptives.
- Primary hypogonadism.

⭐ Unopposed estrogen therapy (without progestin) significantly increases the risk of endometrial cancer in women with a uterus.

Progestins - The Cycle Stabilizers

Hormonal Implant Actions on Female Reproductive System

Mechanism: Bind progesterone receptors → ↓ GnRH pulse frequency, thicken cervical mucus, and decidualize the endometrium, making it hostile to implantation.
Agents: Levonorgestrel, medroxyprogesterone acetate, etonogestrel, norethindrone.
Clinical Use: Contraception (alone or combined), HRT (to oppose estrogen), dysfunctional uterine bleeding (DUB), endometriosis.
Adverse Effects: Breakthrough bleeding, headache, weight gain. ⚠️ Depot medroxyprogesterone acetate (DMPA) may cause ↓ bone mineral density.

⭐ Progestin Challenge Test: Used to evaluate amenorrhea. Withdrawal bleeding after a progestin course indicates anovulation with adequate estrogen. No bleeding suggests low estrogen or an outflow tract obstruction.

SERMs & Antagonists - The Hormone Hackers

Drug	Mechanism	Agonist Activity	Antagonist Activity	Clinical Use
Tamoxifen	SERM	Bone, Endometrium	Breast	ER+ breast cancer. ⚠️ ↑ risk of endometrial cancer & DVT.
Raloxifene	SERM	Bone	Breast, Endometrium	Osteoporosis, breast cancer prophylaxis.
Clomiphene	SERM	-	Hypothalamus	Ovulation induction (PCOS); blocks E₂ negative feedback, ↑FSH/LH.
Anastrozole	Aromatase Inhibitor	-	-	ER+ breast cancer (postmenopausal). Blocks peripheral estrogen production.
Mifepristone	Progestin Antagonist	-	Progesterone Receptors	Pregnancy termination; causes decidual necrosis.

Contraception - The Cycle Controllers

Combined Hormonal Contraceptives (CHCs): Estrogen + Progestin
- Mechanism: Suppress GnRH, LH & FSH secretion → inhibit ovulation.
- Also thicken cervical mucus & alter the endometrium, making it hostile to implantation.
Progestin-Only Contraceptives (POPs or "Minipill")
- Mechanism: Primarily thicken cervical mucus. Ovulation is inhibited inconsistently.
- Fewer contraindications than CHCs, especially regarding thrombosis risk.

⭐ The estrogen component of CHCs increases the risk of venous thromboembolism (VTE), MI, and stroke. This risk is significantly amplified in women >35 years of age who smoke.

High‑Yield Points - ⚡ Biggest Takeaways

Unopposed estrogen significantly increases the risk of thromboembolic events and endometrial cancer.

Tamoxifen acts as a breast antagonist but a uterine agonist, raising endometrial cancer risk.

Raloxifene is a bone agonist used for osteoporosis and does not carry the same uterine risk.

Clomiphene induces ovulation by acting as a hypothalamic estrogen antagonist.

Progestins are key for contraception and endometrial protection from unopposed estrogen.

Aromatase inhibitors like anastrozole treat ER+ breast cancer in postmenopausal women.

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