Video 2 Notes: Pharmacology of Hormonal Contraceptives (Benefits, Risks, Use, Interactions, Emergency Contraception)

Benefits of hormonal contraceptives

The primary benefit of taking hormonal contraceptives is the prevention of an unwanted pregnancy. As discussed in the video, combined oral contraceptives and progestin‑only contraceptives are highly effective, reliable and reversible forms of contraception. They also reduce negative aspects of menstruation, specifically reducing blood loss (menorrhagia) and pain (dysmenorrhea). They may also lessen symptoms such as menstrual tension; however, they can adversely affect mood in some individuals, a point acknowledged for consideration in prescribing. They may lessen symptoms from uterine fibroids and ovarian cysts, reduce benign breast disease, and importantly reduce the risk of ovarian and endometrial cancer, as well as reduce the risk of pelvic inflammatory disease.

Risks and minor side effects

On the slide the risks are categorized as minor and are drawn from the Stuart and Black article referenced in the first video. These minor or common side effects include nausea, breast tenderness, bloating, fluid retention, headache, dysmenorrhea, decreased libido and breakthrough bleeding. It is recognised that additional unwanted effects may occur beyond those listed, and patients and prescribers should be aware of potential variations in tolerability.

Major risks and cancers

The major risks associated with combined oral contraceptives include venous thromboembolism (VTE), arterial thromboembolism (ATE), and a small increased risk of breast cancer and possibly cervical cancer. The cervical cancer risk is now thought to be largely associated with HPV infection. A shift in perception of hormonal contraception risks has been discussed, including the emergence of a view labelled as hormone phobia by some sources and amplified by media such as Telegraph coverage.

Thromboembolism risk: data and mechanism

Data from the Therapeutics Goods Administration (TGA) dated 02/2016 and still referenced from the current website indicate that without hormonal contraceptives the baseline risk is about 2\ \text{cases in every } 10{,}000\ \text{women per year}. This risk increases for users of combined hormonal contraceptives to about 5-12\ \text{cases in every } 10{,}000\ \text{women years}, with variability depending on the progestin component. Arterial thromboembolism is described as rarer than venous thromboembolism, with no explicit figures provided. The mechanism involves estrogens altering the production of clotting and anti‑clotting factors, effectively shifting the hemostatic balance toward a prothrombotic state, a point attributed to Anita Nelson in the slide.

A key line of inquiry in the video is whether risk differs by the progestogen generation. The comparison of second‑ versus third‑generation progestogens shows a rise from about 5-7\ \text{cases} to 9-12\ \text{cases per } 10{,}000\ \text{women-years}, prompting questions about the underlying mechanism. The proposed explanation is that estrogens create a prothrombotic state and that the apparent difference between second and third generation progestogens may relate to indirect estrogenic effects, with the second generation having more androgenic activity that could mitigate some prothrombotic effects, whereas third generation progestogens were developed to reduce androgenicity. The speaker emphasises that the effect is not a direct effect of progestins themselves, but rather an estrogen‑mediated mechanism influenced by progestin choice.

Overall, the video suggests that for women at low baseline risk of cardiovascular disease and breast cancer, combined oral contraceptives remain an appropriate method of pregnancy prevention. The author notes that there is a broader public health perspective where the risk of dying from other common activities may exceed the risk associated with using oral contraceptives, encouraging careful interpretation of risks in context.

How hormonal contraceptives are used and factors that reduce effectiveness

The lecture outlines the standard usage patterns and factors that can compromise effectiveness. Combined pills are available in 28‑day regimens with active tablets taken for 21,\ 24,\ or\ 26 days, followed by inactive tablets. If an active pill is missed by more than 12\text{ hours} or if vomiting occurs, effectiveness may be reduced, and guidelines in the product information sheets should be followed (these sheets are updated regularly). Progestin‑only pills are taken continuously with no inactive pills, and if a pill is missed by more than 3\text{ hours}, effectiveness may be reduced.

Beyond adherence, drug interactions can reduce effectiveness. The oral contraceptives’ metabolism is primarily hepatic and involves phase I oxidative metabolism and phase II conjugation. For estrogens, specifically ethinyl estradiol, the primary phase I route is via the enzyme \text{CYP3A4}, with a lesser contribution from \text{CYP2C9}; phase II metabolism involves sulfation and glucuronidation. The transcript suggests ethinylestradiol is not highly sensitive to CYP3A4 inhibition, though the speaker acknowledges potential errors in that statement. In any case, conjugation remains important for estrogen metabolism. For progestogens, metabolism also involves \text{CYP3A4} and multiple conjugation pathways. The key practical point is that any drug that induces or inhibits \text{CYP3A4} can affect the metabolism and thus the effectiveness of both estrogens and progestogens.

The speaker identifies four drug classes that are commonly implicated as inducers of \text{CYP3A4}: antiepileptics, antiretrovirals, antibiotics, and herbal antidepressants (notably St. John’s wort). Among these, phenytoin, carbamazepine and St. John’s wort are strong inducers of \text{CYP3A4}, and therefore significantly raise the risk of reduced contraceptive effectiveness. Efavirenz is highlighted among antiretrovirals as a concern, while other antiretrovirals are described as having limited interactions. Regarding antibiotics, there has historically been concern about interactions due to effects on estrogen recycling; however, current guidance suggests that only rifampicin‑like antibiotics warrant extra caution or dose adjustments, while many other antibiotics do not reliably compromise contraceptive effectiveness. The overall takeaway is that drug interactions are a major consideration when prescribing hormonal contraceptives and must be evaluated for each patient.

Emergency contraception: morning‑after options

Emergency contraception is discussed as a complement to the regular use of hormonal contraception. The two main agents are levonorgestrel (the traditional “morning after pill”) and ulipristal (a progesterone receptor modulator). Both work primarily by preventing or postponing ovulation through blunting the LH surge. They are well tolerated and available over the counter in pharmacies. Common adverse effects include vomiting. Efficacy data presented include: about 84\% efficacy when taken within 72\ hours of unprotected intercourse, and estimates of pregnancies occurring with use: 1\% for ulipristal within 24\ hours and 2.5\% for levonorgestrel within 24\ hours.

Summary and practical implications

The video reiterates that hormonal contraceptives are highly effective at preventing unwanted pregnancies and offer additional health benefits, but there are risks and potential adverse effects. Their effectiveness can be compromised by illness, non‑compliance, or drug interactions. They may be used as a morning‑after option after unprotected sex, and there are relatively few adverse effects with a good level of effectiveness when used for emergency contraception. The speaker urges students to be able to list examples of benefits and drawbacks, state factors that reduce effectiveness, and describe general usage for regular and emergency contraception. A reading list accompanies the module, and three appendices provide extra statistics and considerations. A small, practical document is recommended for thinking about all the factors involved; the material is framed as a simple starting point, with acknowledgment that real‑world practice is more complex.

Cancer risk context and other statistics

Appendix materials include additional statistics illustrating risk patterns related to thromboembolism and various cancers. The ovarian and endometrial cancer risks appear reduced with contraceptive use, and there is a suggestion of possible reduced risk of colorectal cancer as well. The overall framing invites readers to balance individual risk with the broad public health context rather than relying on isolated figures.

Practical notes on sources and caveats

The content references the Therapeutics Goods Administration (TGA) data and a cited article by Stuart and Black. The transcript includes a note about possible errors or inconsistencies in certain statements (e.g., some comments about ethinyl estradiol sensitivity to CYP3A4 inhibition). Readers should consult current product information sheets and updated guidelines for the most accurate, evidence‑based, and up‑to‑date recommendations. The material also highlights ongoing debates around hormone phobia and public perception, encouraging critical appraisal of media sources when discussing risks with patients.

Key takeaways for exam preparation

Hormonal contraceptives are highly effective, reversible, and offer menstrual cycle benefits but carry risks such as VTE, ATE, and possible cancer associations, which vary with progestin type and patient factors.
VTE risk is increased with combined hormones and depends on the progestin; baseline risk is approx. 2\times 10^{-4} per year, increasing to a range of 5-12\ \text{per }10{,}000\text{ woman-years} with combined regimens; arterial risk is rarer. Mechanistically, estrogen shifts hemostasis toward a prothrombotic state.
Second vs third generation progestogens show differing VTE risk patterns; explanations involve estrogenic effects and changes in androgenicity; the direct role of progestins is not clear.
Drug interactions via \text{CYP3A4} can reduce effectiveness; strong inducers include phenytoin, carbamazepine, and St. John’s wort; efavirenz is a notable antiretroviral concern; rifampin‑like antibiotics may require dose adjustments.
Usage patterns differ between combined pills (28‑day cycle with active and inactive pills) and progestin‑only pills (continuous). Missed doses beyond certain windows reduce effectiveness (combined: >12 hours; progestin‑only: >3 hours).
Emergency contraception options (levonorgestrel and ulipristal) are over‑the‑counter; they work by delaying ovulation, with efficacy figures provided for use within specified time frames.
Real‑world considerations emphasize balancing benefits and risks, and recognizing that the risk of adverse events must be weighed against the benefits of pregnancy prevention and other health outcomes.
Appendices and reading lists provide further context and statistics on thromboembolism and cancer risks.