I missed a dose of warfarin — what should I do?

What to do right now

Work out how many hours have passed since you would normally have taken it. Warfarin is dosed once a day and its effect builds over days rather than hours, so a dose taken a few hours late is close to a dose taken on time. A dose taken alongside tomorrow's is a double dose, whatever your intention.

Then record it. The date you missed a dose is genuinely useful clinical information — if your INR comes back low next week, that missed dose is very likely the explanation, and knowing that stops your clinic from changing a prescription that was never the problem.

Why you must never double up

Doubling feels like the intuitive fix, and it is the one thing every anticoagulation service asks you not to do. Warfarin does not work dose-by-dose the way a painkiller does. It works by suppressing the production of clotting factors, and the effect of any single dose is spread across roughly two to five days.

Taking two doses together does not restore yesterday. It pushes tomorrow's INR above where it should be, and because the effect is delayed you will not see the consequence until a day or two later — often after you have stopped thinking about it. A missed dose leaves you briefly under-anticoagulated. A doubled dose leaves you over-anticoagulated at a moment nobody is expecting, which is the more dangerous of the two.

What a missed dose does to your INR

One missed dose typically pulls your INR down by a modest amount, showing up over the following two to four days and recovering over the week after that. How far it falls depends on your dose, how stable you were and how your body handles warfarin.

The consequence is rarely dramatic in isolation. It matters because of what it does to your time in therapeutic range — a single miss can cost you the better part of a week of in-range days, and a handful of misses across a few months is one of the most common reasons a TTR score comes back below 60%.

If you missed two or more days

This is no longer a self-managed situation. Two or more consecutive missed doses can drop your INR well under your target and leave you meaningfully under-protected against the clot your warfarin was prescribed to prevent.

Ring your anticoagulation clinic, tell them exactly which days were missed, and follow what they tell you. They may bring your next test forward. Do not attempt to make up the shortfall yourself.

What to tell your clinic

Useful information, in order of usefulness:

• Which dates were missed — not "a few weeks ago"
• Whether you took the dose late or skipped it entirely
• Whether you doubled up, if you did — say so, they need to know
• Anything else that changed around the same time: a new medication, illness, a period of poor eating

Specific dates are what let a clinician line up your missed doses against your INR results and see whether the two explain each other.

How to stop it happening again

Most missed doses are not carelessness. They are the predictable result of a medication whose amount changes by weekday and changes again whenever the clinic calls — which makes it genuinely hard to remember what you were meant to take, let alone whether you took it.

This is the problem Coagly was built around, and it is why the whole of it is free:

• The reminder names the dose. Not "time for your medication" but the actual amount due today, drawn from your weekly schedule. A reminder announcing last week's dose is worse than no reminder at all.
• It rewrites itself when your prescription changes. Update your dose after a clinic call and every future reminder is already correct.
• Mark it taken from the home screen. A widget shows today's dose with a single button, so the answer to "did I take it?" is on the screen rather than in your memory.
• Your dose history is a record. Every missed day is logged with its date, so when the clinic asks you have the exact answer.

Dose tracking, the daily reminder and appointment reminders are free forever in Coagly. They are the safety net, and a safety net behind a paywall is not a safety net.

Common questions