Short answer: Observational studies suggest so, but the labels do not make that claim. In a French case-control study and a UK study of over 80,000 women with clots, oral estrogen was linked to more clots while patches and gels were not. No randomized trial has compared them, and every estrogen patch label still carries the same boxed warning, saying the risks cannot be ruled out for other routes.
The clot numbers in estrogen labels come from the Women's Health Initiative (WHI), which tested pills. In the estrogen-alone arm, clots in the legs or lungs ran 30 per 10,000 women-years on conjugated estrogens versus 22 on placebo; with added medroxyprogesterone, 35 versus 17 (Climara section 5.1). See Women's Health Initiative.
The Climara boxed warning says only daily oral 0.625 mg conjugated estrogens was studied in that arm, so the relevance of the findings to other routes is not known, and without such data the risks cannot be definitively excluded. That is why patches, gels and sprays carry the same boxed warning as pills. The label also says to stop estrogen at least 4 to 6 weeks before surgery linked to clots, if feasible.
| Study | Who | Oral estrogen | Patch or gel |
|---|---|---|---|
| ESTHER (Canonico 2007) | 271 women with a first unexplained clot and 610 controls, ages 45 to 70, France | Odds ratio 4.2 for a clot | Odds ratio 0.9 (no clear rise) |
| Vinogradova 2019 | 80,396 women with a clot and 391,494 controls, ages 40 to 79, UK | Odds ratio 1.58 | Odds ratio 0.93 (no clear rise) |
| Renoux 2010 (stroke) | 15,710 women with a stroke and 59,958 controls, ages 50 to 79, UK | Rate ratio 1.28 | 0.95 overall; 0.81 for low-dose patches, 1.89 for high-dose patches |
The UK clot study also found differences by pill type: conjugated equine estrogen with medroxyprogesterone had the highest odds ratio (2.10), and estradiol pills had lower odds than conjugated estrogens. In ESTHER, micronized progesterone was not linked to clots, while one group of progestins was.
All three studies looked back at women who were already using one form or another. Women given patches may differ from those given pills in ways the researchers could not fully measure, and the stroke study says some of that bias cannot be ruled out. Odds ratios also describe relative risk; a clot is still uncommon for any single woman (see relative vs absolute risk).
The stroke result shows the dose matters too: high-dose patches were linked to more strokes in that study.
Route, dose and progestin type are choices to talk through with the prescriber, especially with a past clot, a family history of clots, smoking, obesity or upcoming surgery, which the labels list among the risk factors to manage. Dose Track can keep the product, dose and change days in one log for that visit.
Read more on Dose Track: Women's Health Initiative · Climara vs Vivelle-Dot · Estradiol tablet side effects · Menopause