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Assumed Daily Dose (ADD) methodology


This section explains the use of Assumed Daily Doses (ADDs) for measuring medicine utilisation in the Innovation Scorecard. It discusses why ADDs are used, how they are used in calculations, and the principles applied to assign ADDs. The page includes examples of how to apply the rules for assigning ADDs, and worked examples of ADD calculations.

ADD definition

An Assumed Daily Dose (ADD) is a prescribing measure developed specifically for the Innovation Scorecard. It is similar to the internationally recognised Defined Daily Dose (DDD).

An ADD is a unique value for each presentation of a medicine. It is based on the strength and form of the drug, for example vials or 150mg tablets. It is also based on the recommended frequency of use for the presentation’s main indication, for example, one a day, or every 2 weeks.

When first introduced to the Innovation Scorecard in January 2016, the measure was called an Actual Daily Dose. From the October 2023 publication, it has been renamed to Assumed Daily Dose. The new name reflects that it is a derived value based on assumptions about how the medicine is used such as age, weight, type and severity of disease, rather than actual usage by individual patients.

ADDs in the innovation scorecard

Medicine groupings are used in the Innovation Scorecard where there are several medicines as options for treatment of a condition or similar conditions.

To report on the total use of medicines within a grouping, a standard unit of measurement is needed. This allows us to add together the use of the different medicines in a fair and meaningful way.

For example, a grouping could include medicine A for which the dose is one 10mg tablet once a day, and medicine B for which the standard dose is one 2.5mg tablet twice a day. To add together the number of tablets would give too much weight to medicine B. Adding together the number of milligrams would give too much weight to medicine A. Similarly, a grouping could include medicines that have different routes of administration such as tablets taken orally and liquids given intravenously.

The Defined Daily Dose (DDD) unit of measurement is defined by the WHO Collaborating Centre for Drug Statistics Methodology. It assigns a single assumed average dose per day for a medicine formulation at a chemical substance level. This is used to report the use of some individual medicines within the Innovation Scorecard.

However, there are limitations in using DDDs to report medicine use:

  • DDDs are calculated at the chemical substance level and may not reflect any available presentations for the medicine
  • DDDs are only assigned once a year, so there may be a gap between a medicine being added to the Innovation Scorecard and the DDD being published
  • not all medicines can be assigned a DDD, for example if the dosing schedule is highly dependent on patient characteristics
  • DDDs assigned on an international basis may not reflect prescribing practices in England

The source data for the Innovation Scorecard is at presentation level. We assign an ADD to each presentation.

The advantages of using ADDs are that the ADD values can match the prescribing patterns. For example, the amount of a presentation that is specifically used for reduced doses is counted as the relevant number of reduced daily doses. This is instead of counting a smaller number of the standard dose. Another advantage is that an ADD may be able to be created where no DDD has been published. The published DDD may also not apply to the presentation, such as an initiation specific pack or strength.

ADDs in innovation scorecard calculations

The usage of a drug grouping where all the presentations have assigned ADD values is calculated over several steps.

  1. For each presentation of each drug, the total ADDs for presentation X of drug A is found by dividing the total number of units of presentation X by the ADD value.
  2. The total ADDs for drug A is found by adding together the total ADDs for each presentation.
  3. Steps 1 and 2 are repeated for each drug within the grouping of medicines.
  4. The total ADDs for the grouping is found by adding together the total ADDs for each drug.

ADD calculations worked example

Drug Presentation Dose ADD Prescribing
A 5mg tablet 5mg twice daily 2 tablets 100 tablets
A 10mg tablet 10mg once daily 1 tablet 100 tablets
A 5mg/5ml oral solution 7.5ml once daily 7.5mg 750mg
B 20mg capsule 20mg twice daily 2 capsules 50 capsules
B 10mg patch 10mg once daily 1 patch 50 patches

For drug A:

  • the total ADDs for 5mg tablets is 100 tablets divided by 2 tablets, which equals 50
  • the total ADDs for 10mg tablets is 100 tablets divided by 1 tablet, which equals 100
  • the total ADDs for 5mg/5ml oral solution is 750mg divided by 7.5mg, which equals 100

Therefore, the total ADDs for drug A is 250. This is found by adding together the total ADDs for 5mg tablets, 10mg tablets and 5mg/5ml oral solution, which is 50 plus 100 plus 100.

For drug B:

  • the total ADDs for 20mg capsules is 50 capsules divided by 2 capsules, which equals 25
  • the total ADDs for 10mg patch is 50 patches divided by 1 patch, which equals 50

Therefore, the total ADDs for drug B is 75. This is found by adding together the total ADDs for 20mg capsules and 10mg patches, which is 25 plus 50.

For drugs A and B the total ADDs is 325 ADDs. This is found by adding the 250 for drug A and the 75 for drug B.

Rules for assigning ADDs

We apply the following guiding principles when assigning an ADD to a presentation of a medicine. This makes sure that ADDs are assigned consistently and transparently.

The rules are applied when an ADD is first needed to be assigned to a presentation. This may be needed the first time the presentation appears in the prescribing data used in the Innovation Scorecard. It can also happen when a medicine previously reported as an individual medicine is added to a grouping. There is currently no routine review process for ADDs following this initial assignment. However, ADDs may be updated if relevant information is noticed during the production process of a new release of the Innovation Scorecard.

For some medicines, the recommended dose and frequency are more complex and require assumptions specific to that medicine when assigning the ADD.

A file showing the assumptions made for each medicine for which ADDs have been assigned is included in the resources section of the overview chapter.

General rules

A presentation of a medicine is selected for treatment use to minimise the number of units used for a dose, for example, tablets, pens, or vials.

Each presentation is used for a recommended maintenance dose unless the presentation is specifically designed for initiation. A presentation designed for initiation, such as a different strength or a titration pack, might be different from one used for a maintenance dose.

If a presentation is designed for use by children, the ADD for that presentation will be based on the child maintenance dose. This is different from the DDD which is usually based on the adult maintenance dose.

Where a DDD is published for the medicine, you should follow the assumptions used in assigning the DDD. If these assumptions are not followed, you should document where departure from the assumptions is intentional.

Treatment frequency and duration

Where a presentation will be used to give doses at intervals less frequently than daily, calculate the ADD as the dose divided by the number of days in the treatment period. Where the interval varies between information sources, you should rely on the DDD. If the DDD is not available, the manufacturer’s information or the NICE TA should be used.

Where a presentation is recommended to be given for a defined treatment period, calculate the ADD over the treatment period.


Where a presentation is specifically designed for initiation of treatment, the ADD will be assigned based on this use.

Where the presentation is an initiation pack containing multiple doses, calculate the ADD as the total in the pack divided by the number of days for which the pack is used.

Whole vial use

Where part of a vial or other unit would be used for a dose and the remainder discarded, the ADD is calculated as using the whole vial.

Units and rounding

For tablet or sachet presentations given daily, define the ADD in tablets or sachets.

For tablet or sachet presentations used to give doses at intervals less frequently than daily, define the ADD in units of the active ingredient, for example, milligrams.

Round ADD calculations consistently with the DDD where relevant.

If the calculated value can be expressed exactly to 2 decimal places, for example, 1.75 tablets, use this value.

Otherwise, round to 2 decimal places if the value is less than one of the relevant unit of measurement for example mg, mcg. Round to one decimal place if the value is more than one unit, or to the nearest whole number if more than 10 units.

If presentations of the same medicine would be rounded differently, round to the same number of decimal places for all the presentations.

Examples of applying the ADD rules

Presentation selection

Drug A is available in 20mg, 30mg, and 40mg tablets.

The recommended dose is 40mg once daily. Adverse effects may be managed by dose reductions.

We assume that the 20mg tablet is selected when a reduced dose is required, and would not be selected to give a 40mg dose as 2 x 20mg tablets. The ADD for the 20mg tablet is therefore one tablet.

Use for maintenance dose

The initial dose of drug B comprises two 300mg infusions 2 weeks apart.

The maintenance dose of drug B is 600mg every 6 months.

The only presentation available is a 300mg dose. This may be used for initial doses or maintenance doses.

Because we cannot identify initiation use separately, we assume that all the reported use is for maintenance doses. Applying the ‘divide by treatment period’ rule, the ADD is 600mg divided by 182 days = 3.3mg.

Child maintenance doses

Drug C is available as a sachet of granules, with a recommended dosage for children aged under 12. In assigning the ADD we assume that the sachet is used for the recommended age group.

Specific initiation presentations

The recommended dose for drug D is 15mg twice daily for 3 weeks, followed by 20mg once daily for continued treatment.

We assume that the 15mg presentation is only used for initiation doses, with an assigned ADD of 2 tablets. The ADD for the 20mg presentation is one tablet.

Following the DDD assumptions

The treatment cycle for drug E is 5 consecutive days of treatment in the first year of treatment, and 3 consecutive days of treatment in the second year of treatment. The published DDD assumes an average of 4 days of treatment per year, and we apply the same assumption in assigning the ADD.

The recommended dose for drug F is 3mg/kg every 4 weeks. The DDD methodology document states that when the recommended dose refers to body weight, an adult is considered to be a person of 70kg. The recommended dose would therefore be 210mg.

However, the dose is recommended to be given as a whole number of vials, with a dose of 200mg for patients in the weight range that includes 70kg. The DDD is assigned as 200mg divided by 28 days = 7.1mg. We apply the same assumptions in assigning the ADD.

Departing from the DDD assumptions

Drug G is available as 10mg tablets or 25mg tablets, with the recommended dose for each strength of one tablet daily.

The published DDD is 17.5mg, being an average of the 2 strengths.

As the ADD is assigned at presentation level, we do not use this assumption. We assign the ADD for each presentation as 1 tablet daily.

Treatment frequency

For drugs H to L, we assign an ADD to a presentation by dividing the amount of active ingredient over the interval between doses.

Drug Dose Frequency Time in days Calculation ADD
H 75mg every 2 weeks 14 75 divided by 14 5.4mg
I 225mg monthly 30 225 divided by 30 7.5mg
J 140mg every 4 weeks 28 140 divided by 28 5mg
K 600mg every 6 months 182 600 divided by 182 3.3mg
L 10mg daily for 2 weeks per year 365 10 times 14 divided by 365 0.38mg

Initiation pack

An initiation pack presentation is available for drug M containing multiple doses of different strengths for a patient to build up to the recommended daily dose.

We assign the ADD for the initiation pack as the total number of tablets in the pack divided by the number of days supply included in the pack.

Treatment days Number of days Dose Frequency Total tablets
Days 1-3 3 0.5mg 1 daily 3
Days 4-7 4 0.5mg 2 daily 8
Days 8-14 7 1mg 2 daily 14
Total 14     25

The ADD for the initiation pack is 25 tablets divided by 14 days = 1.8 tablets, rounded to one decimal place.

Whole vial use

Drug N is available as a 10mg per vial presentation. The dose for drug N is 21mg every 3 weeks. This dose will require the use of 3 of the 10mg vials, with an unused amount being discarded.

We assign the ADD as the amount of the medicine in the number of whole vials used to give the dose, divided by the number of days in the treatment period. Note this may be greater than the amount administered to the patient.

For drug N, the ADD is 3 x 10mg = 30mg divided by 21 days = 1.4mg.

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Background Quality notes

Pages in this publication

  1. Overview
  2. Background and introduction
  3. Estimates Report
  4. Assumed Daily Dose (ADD) Methodology
  5. Background Quality notes
  6. Guidance and glossary
  7. Guide to the underlying data