When a Dose Is Late or Forgotten: What to Do If You Miss Your Medicine

Written by: 齋藤 直裕 (Pharmacist)

Most medicines that people are told to keep taking because of a health problem or illness are taken every day. I’m sure many of you have come up with all sorts of ways not to forget them.

Even so, it happens: you set out today’s dose, but in the bustle of daily life something else distracts you, and by the time you notice you’ve forgotten it, it’s already time for the next meal. In everyday life, we sometimes forget a dose by accident and, when we notice, aren’t sure what to do.

“If the daily amount is fixed, can I take two doses together?” “Nothing happens when I miss one, so can I just skip it and start again with the next dose?” “Should I take it now and push back my next meal?” Are these really the right decisions?

The general advice is often “Don’t take two doses at once” or “Take it when you remember, but if the next dose is due soon, skip the missed one.” In reality, though, medicines are taken at many different times (once a day, twice a day, before meals and so on), so the same approach doesn’t apply to every medicine.

Why do medicines differ in how often they are taken?

Medicines don’t work the moment you take them; the effect appears after a while. A medicine taken by mouth is absorbed from the stomach and intestines, passes through the liver, where it is first broken down (metabolized), and is then carried by the blood throughout the body, where it takes effect.

After that, the medicine’s components circulate through the body with the blood many times while being excreted in urine and stool, and the effect gradually fades. In other words, the medicine works while it is in the blood, and as it thins out, the effect disappears.

The concentration of a medicine in the blood is called its blood concentration, and it changes greatly depending on how much you take and when.

Does taking more make it work better?

You might think, then, that taking more makes a medicine work better and longer. Alcohol makes an easy example.

Alcohol is absorbed into the blood from the stomach and intestines, passes through the liver, where it is partly broken down, and then circulates through the body. If we think of feeling good as the “effect,” it appears gradually after drinking. Then, as the alcohol circulates in the blood and is excreted, you sober up more and more.

But if you keep drinking or drink a lot, unintended effects (side effects) appear, such as drowsiness or nausea in some people. Medicines are the same: taking more raises the risk of side effects.

Here, how quickly the effect appears is determined by absorption; how strong it is, by blood concentration; and how long it lasts, by metabolism (breakdown) and by excretion in urine and stool. If more alcohol is added before the effect has worn off, the blood concentration keeps building up, making unpleasant effects such as vomiting, drowsiness and memory loss more likely.

The “right amount” differs from person to person

However, some people get drunk on a little alcohol, while others can drink a lot without any change. Differences in breakdown (metabolism) in the liver play a large part in this.

Alcohol is broken down by enzymes in the liver, eventually into water and carbon dioxide, and loses its effect as alcohol. The amount and activity of these enzymes vary from person to person, and this is why some people are said to hold their drink well and others poorly.

With alcohol and medicines alike, the effect on the body varies with ethnicity, sex, age and build, and with the function of the liver, which detoxifies, and the kidneys, which excrete. That is exactly why each person has their own “right amount.”

How are doses and frequency decided?

How often a medicine is taken is determined by how long its effect lasts. A medicine whose effect lasts a full day after one dose is taken once a day; one that wears off in half a day, twice a day; one that works for about 8 hours, three times a day; and so on.

Some medicines act for a long time because their ingredients stay in the body for a long time; others are designed so that the tablet itself dissolves gradually in the stomach and intestines, lasting longer and reducing how often they need to be taken.

How a medicine should be used is determined through many clinical trials during the approval process. Guidelines are set with the greatest care from enormous amounts of data, according to symptoms, physical condition, age, build and so on, but because we are dealing with the human body, unexpected things still happen.

That is why patients are asked to take medicines in the amounts and at the times derived from large amounts of data, and at each subsequent appointment, the doctor checks whether the intended effect is appearing and whether there are problems such as side effects.

The effects of taking medicine incorrectly

However good a medicine is, it can’t be expected to work if it never enters the body because a dose was forgotten. And if you mistakenly take more than prescribed, such as two doses at once, unwanted effects may appear.

What’s more, if the medicine isn’t taken correctly, the doctor can’t judge at the next appointment whether it is appropriate. It is worth knowing that taking medicine correctly not only brings out its benefits and prevents side effects but also helps the doctor plan the right treatment.

When you notice a missed dose

Even if you notice you’ve missed a dose, there’s no need to panic. A painkiller for back pain, an antibiotic started because of a fever, a medicine taken because you were told your blood pressure is high… In fact, what a missed dose means and how it affects you differs completely depending on the medicine. The decision is then made in light of the medicine’s characteristics.

For example, with a painkiller taken once a day after breakfast, you would take it when you remember; but to spare the stomach, the decision would be to take it after lunch if you can, and if it is already evening, to skip it and resume the usual single dose the next day. In this case, the risk of a missed dose is something like your back pain coming back.

Advice from a professional

When you pick up your medicine at the pharmacy, I recommend asking what to do if you miss a dose. Also tell the pharmacist how you take your medicines at home day to day and at what times, and check that this way of taking them is fine.

Above all, correctly understanding what kind of medicine you are taking, and what it is for, is what counts when something goes wrong.

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About the author: 齋藤 直裕 (Pharmacist)

Graduated in pharmacy from Nihon University. Certified Sports Pharmacist. A home-visit pharmacist actively involved in home healthcare (as of the time of writing).

This article is a contribution from a medical or care professional, re-edited by our editorial team. It provides general information as of the time of writing, and symptoms and circumstances differ from person to person. For specific decisions, please consult your doctor, dentist, pharmacist or another professional.

This is an English translation of a column originally published in Japanese by Next Co., Ltd.

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