Emergency contraceptive pills in Canada
Bibliographic record
Abstract
Background: Two emergency contraceptive pills (ECPs) are licensed in Canada to prevent pregnancy after unprotected intercourse or suspected contraceptive failure. Both inhibit or delay ovulation. Levonorgestrel (PLAN B® and generics) has been used since the early 1970’s for “morning after” contraception, and was approved in Canada in 1999 for use within 72 hours (3 days) of sexual intercourse. Ulipristal acetate (ella®) was approved in Canada in 2015 for use within 120 hours (5 days). It is uncertain whether one drug is more efficacious beyond 72 hours after sexual intercourse, or for people whose body weight exceeds 80 kg or BMI (body mass index) exceeds 30 kg/m2 . In British Columbia, generic levonorgestrel is easy to obtain and free of charge. Ulipristal requires a prescription and costs about $40. Methods: We conducted a systematic review to compare the efficacy and safety of levonorgestrel with ulipristal. Results: Two randomized controlled trials (RCTs) compared levonorgestrel with ulipristal for emergency contraception. For use within 72 hours (3 days) of unprotected intercourse, we found no significant difference in pregnancy rates and short-term safety between levonorgestrel and ulipristal. From 72 to 120 hours (3 to 5 days) of unprotected intercourse, comparative efficacy is not well established - primarily related to small sample sizes. Limited and inconclusive data from one non-randomized study suggest consistent efficacy of ulipristal up to 120 hours, whereas an analysis of 4 RCTs of levonorgestrel suggested that its efficacy decreased only beyond 96 hours after intercourse. Based on similarly low quality data, there has been concern that efficacy of both levonorgestrel and ulipristal may decrease at body weights >80 kg or BMI >30 kg/m2 . This is challenged by the findings of 2 reviews, and by a recent RCT. Conclusions: Within 72 hours (3 days) of unprotected intercourse, the relative efficacy of levonorgestrel and ulipristal to prevent unwanted pregnancy is not established conclusively. From 72 to 120 hours (3 to 5 days), relative efficacy is also not well established. It remains uncertain whether body weight >80 kg or BMI >30 kg/m2 reduce efficacy of ECPs at standard doses, at any time point.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.004 | 0.026 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.002 |
| Bibliometrics | 0.006 | 0.012 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.024 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".