You’ve seen the headline. Some version of it turns up every few months: this common tablet causes blood clots. And if you happen to be taking that tablet, the rest of your day has a low hum underneath it.
Here’s the thing worth understanding, and it’s the thing those headlines depend on you not knowing.
There are two ways to describe the same risk, and only one of them sells.
Say a medication takes a risk from 2 in 10,000 up to 4 in 10,000. Both statements below are completely true:
- “It doubles your risk.”
- “It affects 2 additional people out of every 10,000.”
The first is the headline. The second is your life. A doubling of a very small number is still a very small number, and almost every medication scare you’ve ever read is built in that gap — a real finding, reported in the format that makes it sound largest.
None of this means the risks are fictional. Some are real, one is considerably larger than people assume, and in several cases there’s a simple switch that removes most of the risk entirely. But you can’t make a sensible decision from a multiplier. You need the actual numbers.
So here are some.
The Pill: The Comparison Nobody Prints
Combined birth control pills contain estrogen, estrogen nudges blood toward clotting, and the effect is real. Here’s the scale of it, in clots per 10,000 women per year:
- Not pregnant, not on the pill: roughly 1 to 5
- On a combined pill: roughly 3 to 9
- Pregnant: roughly 5 to 20
- In the twelve weeks after giving birth: roughly 40 to 65
Read that list twice.
Pregnancy carries a higher clot risk than the pill. The weeks after childbirth carry many times more. Which means that for a woman taking the pill to avoid pregnancy, the honest comparison isn’t “pill versus nothing.” It’s “pill versus the thing the pill prevents” — and on clot risk alone, the pill comes out ahead.
That single comparison is missing from essentially every article ever written on this subject, and without it the numbers are meaningless.
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The picture changes if you smoke and you’re over 35, if you’ve had a clot before, or if you carry an inherited clotting disorder. Those combinations matter, and they’re worth an actual conversation. But that’s a different statement from “the pill causes clots.”
Hormone Therapy: The Switch That Changes the Answer
This is the most useful thing on the page, and it’s a genuine decision you can make.
Oral estrogen — a tablet — is swallowed, absorbed through the gut, and routed straight through the liver before it reaches the rest of you. The liver responds by producing more clotting factors. That’s the mechanism, and it’s why oral HRT carries a measurable clot risk.
Estrogen through the skin doesn’t do that. A patch or a gel delivers it into the bloodstream directly, skipping the liver pass entirely, and the clotting factors never get the signal. The evidence has been consistent enough for long enough that guidelines now reflect it: transdermal estrogen isn’t associated with the increased clot risk that the tablets carry.
So a woman who has been quietly enduring menopause symptoms because she read something frightening about HRT and clots may be avoiding the wrong thing. The risk she read about is largely about the route, not the hormone. That’s a five-minute conversation and a different prescription.
Testosterone: This One Is Out of Date
Worth being direct about, because the warnings still circulating are no longer current.
For a decade, testosterone carried a boxed warning about cardiovascular risk, added in 2014 after reports of heart attacks and strokes. The FDA required the manufacturers to run a proper trial to settle it.
That trial — TRAVERSE — enrolled over 5,000 men aged 45 to 80 who already had heart disease or were at high risk for it. Precisely the group the warning was about. The result: major cardiac events occurred in 7.0 percent of men on testosterone versus 7.3 percent on placebo. No increase. The trial also found no increase in prostate cancer.
In February 2025, the FDA removed the cardiovascular language from the boxed warning on every testosterone product, and now requires the TRAVERSE results to appear on the label instead. A blood pressure warning was added — testosterone does raise it modestly, and that’s worth monitoring. But the heart attack warning that scared a lot of men away from treatment they needed has been retired by the agency that wrote it.
One thing before you read on: don’t stop anything on your own. Not the pill, not HRT, not a cancer treatment. Every drug in this article is prescribed because the thing it treats is worse than the risk it carries — and some, stopped abruptly, are more dangerous than continuing. The right move is never quitting quietly. It’s asking whether your risk factors change your calculation.
And there’s one entry ahead that’s genuinely different from the others. The risk is larger. It’s dose-dependent. Millions of people take it for years without a prescription, without a doctor’s involvement, and without any idea it belongs on this list at all.
