Tranexamic acid: what it treats, how to take it, side effects
Last updated September 3, 2026.
Tranexamic acid is an antifibrinolytic - it improves blood clotting by slowing the breakdown of clots. You may know it as Lysteda. A period-only drug: taken only during the days of menstrual bleeding, never around the calendar.
What does it treat?
Heavy menstrual bleeding - reducing the volume of monthly periods.
How do you take it?
Three times a day, with or without food, starting when your period starts, for up to 5 days - and only those days: never take it without a period. The hard caps: no more than 5 days per cycle, no more than 6 tablets in 24 hours. Swallow tablets whole. Missed dose: take it when you remember, then continue the same-day spacing; never double up.
Side effects to know
- Common: headache, tiredness, sinus pain, back pain, stomach pain, and bone, joint, or muscle pain.
- Serious - stop taking it and call your doctor immediately or get emergency care: the allergic set - hives, rash, itching, trouble breathing or swallowing, swelling of face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs, hoarseness; vision changes including color vision; and the clot set - chest pain, shortness of breath, leg pain, swelling, tenderness, redness, or warmth.
Who should not take it?
Anyone who has had a blood clot, has a clotting condition, or has been told they are at risk of one - the answer is probably no. Hormonal contraceptives multiply the clot risk: that combination is a doctor-level decision, stated openly. Flag kidney disease. Tell your doctor if you will receive clot-busting medications such as alteplase or reteplase. If you become pregnant, call your doctor.
When is it an emergency?
Chest pain, shortness of breath, one-sided weakness or trouble speaking, a swollen painful warm leg, or sudden vision change is a 911 call - the clot pattern, taken seriously on this drug. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why only 5 days, and only during my period?
The drug's job is local to the bleeding days: it slows clot breakdown in the uterus, cutting flow while the period runs. Taken without a period, it does nothing useful and adds clot risk for no benefit. The caps are firm: up to 5 days per cycle, maximum 6 tablets in 24 hours, whole tablets only. When the period ends, the drug stops until next month.
What is the blood-clot concern?
A drug that protects clots can protect the wrong clot: history of a blood clot, a clotting condition, or being told you are at risk usually rules it out. Hormonal contraceptives stack their own clot risk on top - that combination is a decision your doctor makes with full knowledge of both. The emergency pattern to know: chest pain, shortness of breath, leg pain with swelling, warmth, tenderness, or redness, and vision changes - stop the drug and get care.
Why did my doctor ask about my birth control?
Because the combination is the key safety question: hormonal contraception plus tranexamic acid multiplies clot risk. Being on the pill does not automatically rule the drug out - it changes the math, and your doctor weighs it. Never start or stop hormonal birth control mid-treatment without telling the prescriber; the risk assessment is tied to the combination.
How much lighter will my periods get?
The goal is meaningfully lighter - many people see flow drop by roughly a third to a half - but the honest answer is individual: judge it over two to three cycles by pad-and-tampon counts and the disruption index (missed activities, nighttime changes). If it is not enough by cycle three, the dose or the diagnosis gets another look - heavy bleeding has fixable causes worth ruling out.
Does it treat the cause of the heavy bleeding?
No - it treats the bleeding itself. Fibroids, polyps, hormone disorders, and bleeding disorders can all drive heavy periods, and each has its own treatment. Tranexamic acid buys normal weeks while the cause is worked out - or, when no cause is found, it is a legitimate long-term monthly strategy. The evaluation conversation continues alongside it.
What happens if I miss a dose during the 5 days?
Take it as soon as you remember that day and keep the same-day spacing - never double up, and never exceed 6 tablets in 24 hours. The drug works while it is in your system during the bleeding days, so steady three-times-daily coverage is what shrinks the flow. Set phone alarms for the days you take it.