Key takeaways
- The 1:20 clonazepam-to-diazepam ratio is a starting estimate, and Professor C. Heather Ashton wrote that her equivalents vary between individuals.
- Too much diazepam shows up as sleepiness, and too little shows up as withdrawal symptoms.
- Oversedation can arrive a week or two into a crossover, because diazepam builds up slowly in the body.
- Professor Ashton’s one-dose-at-a-time crossover exists partly to find each person’s own equivalent.
- A substitution does not always need to be complete.
- Adjusting the diazepam dose with your prescriber is part of the method, not a failure of it.
- If diazepam does not suit someone, returning to the original drug and tapering from it is a sound option.
Is Ashton’s 1:20 Klonopin-to-Valium conversion always right?
No, and Professor Ashton never claimed it was. The 1:20 ratio, where 0.5 mg of clonazepam (Klonopin) is listed as roughly equal to 10 mg of diazepam (Valium), is the starting point of a crossover taper, not the finish line.
If you are part way through a crossover and something feels wrong, you may be wondering whether the ratio is to blame. Perhaps you are sleeping through the afternoon. Or, perhaps the old symptoms are creeping back and the new tablets do not seem to be holding you.
This site’s companion article on a Klonopin taper using Ashton’s 1:20 diazepam conversion explains what the ratio is and walks through her schedule for it. This article asks a different question. How do you tell, during the crossover, that the ratio does not fit you, and what did Professor Ashton say to do about it?
Professor Ashton called her equivalents approximate.
The conversion table in the first chapter of the Ashton Manual, as published at benzo.org.uk, comes with a note that most readers skip. It reads: “These equivalents do not agree with those used by some authors. They are firmly based on clinical experience but may vary between individuals.”
She said the same thing in the surrounding text. The differences in strength between benzodiazepines, she wrote, “have not always been fully appreciated by doctors, and some would not agree with the equivalents given here.” And, in Chapter II, where the schedules live, she repeated it: the equivalent potencies “are only approximate and differ between individuals.”
Part of the reason is in that first chapter as well. In her words, “there is a considerable variation between individuals in the rate at which they metabolise benzodiazepines.” Two people can swallow the same tablets and end up with very different amounts of drug in the blood.
The Maudsley Deprescribing Guidelines (chapter 3, p. 394) use the same figure, stating that “A 1mg dose of clonazepam is equivalent to 20mg of diazepam.” Yet, the same book (chapter 3, p. 335) says that equivalencies “can only be seen as rough estimates, and there can be significant inter-individual differences.” Both sources agree on the number, and both call it an estimate.
A conversion can go wrong in two directions.
Professor Ashton described the problem plainly in Chapter II. A person moved suddenly onto too much diazepam “is liable to become extremely sleepy, but if he is switched suddenly onto a much smaller dose of diazepam, he will probably get withdrawal symptoms.”
So, the ratio can be too generous for one person and too stingy for another. Neither outcome means the Manual is wrong. It means the table did its job as a starting estimate, and the person’s own body is now supplying the correction.
Think of the size chart on the wall of a shoe shop, the one that converts a European size to an American one. The chart is useful, and nobody buys shoes without trying them on. While this is not a perfect analogy, a benzodiazepine conversion table is that chart, and the crossover is the fitting.
What does too much diazepam look like?
Drowsiness is the main sign, and it is often joined by grogginess, unsteadiness on your feet, and slowed thinking. Some people describe feeling drunk without having had a drink. The sign that matters most is drowsiness that keeps growing over the first week or two, rather than settling.
Why would it grow instead of settle? Because diazepam does not reach its full effect on day one. The Maudsley Deprescribing Guidelines (chapter 3, p. 404) note that “Diazepam accumulates upon multiple dosing” and that “Diazepam’s active metabolite N-desmethyldiazepam has a half-life of up to 100 hours.”
In plain terms, the body turns diazepam into a second active substance that leaves very slowly. Each day’s dose is added to what is still there from the days before, and the level climbs for a while before it flattens out. A dose that felt right on day three can be too much by day fourteen.
People also clear it at different speeds. The same page of the guidelines states that “The elimination half-life increases by an hour for every year over 20 years of age,” and page 335 adds that “Extra precautions apply in patients with hepatic dysfunction as diazepam, and other longer-acting drugs, may accumulate.” Older people and people with liver problems may find the table’s dose too strong. A conversion table has never once felt sleepy, so it cannot tell you this. Your body can.
One line of caution belongs here. Heavy sedation, confusion, slowed breathing, or being unable to stay awake, especially after any alcohol, is not a dose-adjustment question. It needs emergency care: call 911.
What does too little diazepam look like?
Too little shows up as the symptoms you were tapering to avoid. Anxiety returns, sleep breaks up, tingling or burning sensations appear, and the familiar withdrawal picture comes back into view. These are the same symptoms people recognize from a missed dose, only slower.
Slower, because clonazepam is fairly long-acting itself. It does not vanish on the day you replace it, so its departure takes days, and the gap left by an undersized diazepam dose opens gradually. Unfortunately, that timing can make it look as if the diazepam “stopped working” when in fact the clonazepam finished leaving.
The two signals can also arrive in the same person at different times. Someone may feel sleepy at first and then, as the clonazepam clears, feel underdosed. That is why a crossover is judged over weeks, not days.
Professor Ashton’s method was built to catch a mismatch.
This is the part of the Manual that gets lost when people reduce it to a table. Professor Ashton did not say to swap all of your clonazepam for diazepam on one day. In Chapter II she wrote: “Making the changeover one dose (or part of dose) at a time avoids this difficulty and also helps to find the equivalent dosage for that individual.”
Read that last clause again. The stepwise crossover is not only a comfort measure. It is the Manual’s way of finding your own conversion ratio, one dose at a time, by watching what each substitution does before making the next.
She went further, writing that “the substitution may not always need to be complete.” In her own worked example, which used Ativan (lorazepam) rather than Klonopin, part of a dose was replaced with somewhat less diazepam than the table would have given, and she noted the person might sleep well on that combination. Her stated goal was the balance point: “The aim is to find a dose of diazepam which largely prevents withdrawal symptoms but is not so excessive as to make you sleepy.”
Of her slow withdrawal schedules she said: “Schedules such as these have worked on real people, but you may need to adapt them for your own needs.” The practical consequence is simple. Take each substitution step slowly enough to judge it, and do not start cutting until the switch has settled. The Maudsley Deprescribing Guidelines (chapter 3, p. 335) describe that pause: “A period of stabilisation (e.g. 2 weeks or longer) on the new drug may be required before commencing a taper.”
While the table gets all the attention, the stepwise switch is where the Manual does its real work. Ashton Manual Guide covers the mechanics of that switch in its article on converting short-acting benzodiazepines to diazepam safely.
Adjusting the diazepam dose is not failing.
If the diazepam is making you sleepy, the fix is less diazepam in the substituted doses, agreed with your prescriber, not pushing on in the hope that it passes. If withdrawal symptoms are showing through, the fix is a little more. Either way, the adjustment is the method working as Professor Ashton designed it.
Change one thing at a time. Then give each change time to show, because diazepam’s full effect lags behind the dose by days. If you cut and switch in the same week, neither you nor your doctor will know which change caused what.
Whatever the adjustment, it is made by moving the dose, never by dropping it. The 2020 benzodiazepine label update from the U.S. Food and Drug Administration (FDA) recognizes withdrawal reactions and the need for gradual dose reduction, and the Manual’s advice is the same. Never stop a benzodiazepine abruptly.
Some readers feel they have let themselves down by needing an adjustment. In this site’s view, the ratio was never a test to pass. Dependence is not addiction, and a person adjusting a prescribed dose with their doctor is doing exactly what the Manual asks. It is a measurement, not a verdict.
What if diazepam does not suit you at all?
It happens, and Professor Ashton said so. “Some people, however, appear to have particular difficulty in switching from Klonopin to diazepam,” she wrote in Chapter II. For them she described tapering directly from Klonopin using specially made small doses, while noting that “this approach to benzodiazepine withdrawal can be troublesome and is not recommended for general use.”
The Maudsley Deprescribing Guidelines (chapter 3, p. 335) allow the same exit: “Other patients may find switching difficult or prefer to taper from the original, familiar drug.” Both books treat the crossover as the usual route and the direct taper as a legitimate second one.
When a person turns out not to tolerate diazepam, going back to the original benzodiazepine and tapering from it is a sound choice, and it is consistent with both books. This may not be discovered right away, since the sedation can take a week or two to declare itself. Going back is not a retreat. It is choosing the drug your body handles better and tapering from there.
The direct route needs small, measured steps, which is where a liquid or specially prepared form earns its place. This site’s clonazepam taper calculator lays out what a gradual schedule from clonazepam itself looks like, as an educational planning tool for you and your prescriber to discuss.
A few questions come up again and again about the 1:20 ratio.
Is 1:20 the same ratio the Maudsley Deprescribing Guidelines use?
Yes. The guidelines (chapter 3, p. 394) state that “A 1mg dose of clonazepam is equivalent to 20mg of diazepam,” which is the Manual’s ratio. They also call such equivalencies rough estimates with significant differences between individuals, which is the Manual’s warning.
Why might Valium feel fine at first and too strong two weeks later?
Because diazepam accumulates. Its active metabolite leaves the body slowly, so each day’s dose stacks on the last until the level plateaus. Age and liver function slow that clearance further, so the plateau sits higher for some people than for others.
Does a crossover have to replace every milligram of clonazepam?
No. Professor Ashton wrote that “the substitution may not always need to be complete,” and her stepwise method lets a partial substitution be judged before anything else is changed. The same principle applies to alprazolam, as described in this site’s article on how a Xanax to Valium conversion works in practice.
Is it a step backwards to return to Klonopin?
No. Both the Manual and the Maudsley Deprescribing Guidelines describe tapering from the original drug as a legitimate route when switching proves difficult. The goal is a gradual taper you can tolerate, whichever drug it is built from.
The table starts the conversation, and your body finishes it.
Professor Ashton gave her readers a table, a method for testing the table one dose at a time, and permission to adapt. Of the three, the permission is the part most often forgotten. The ratio starts the conversation, and your own response finishes it.
The benzodiazepine conversion calculator on this site shows the table’s starting estimate for any benzodiazepine, and the clonazepam taper calculator shows the direct route if that is where you and your prescriber end up. Both are educational planning tools, and neither one knows how sleepy you are. Your doctor needs to hear that from you.
This article is educational. It is not medical advice, and reading it does not create a doctor-patient relationship. Decisions about starting, continuing, or tapering any medication should be made with your own physician.
