ICH M7 guideline on mutagenic impurities, limits and nitrosamines
ICH M7(R2) assesses mutagenic impurities in medicines: five classes, a 1.5 µg/day TTC and four control options. Nitrosamine limits come from FDA and EMA.
ICH M7 guideline on mutagenic impurities
ICH M7 is the ICH guideline for assessing and controlling DNA-reactive (mutagenic) impurities in medicines to limit potential cancer risk. Its default lifetime threshold of toxicological concern (TTC) is 1.5 µg/person/day, but potent groups such as nitrosamines need separate limits (ICH M7(R2) guideline).
Current version of the ICH M7 guideline
The current version is M7(R2), adopted at Step 4 on 3 April 2023 (ICH guideline). The Addendum was adopted the same day. The Q&A had already reached Step 4 on 24 May 2022.
The FDA issued M7(R2) as final guidance in July 2023, together with the Addendum and the Q&A (FDA). In the EU, EMA published it as EMA/CHMP/ICH/83812/2013 on 19 July 2023, effective 30 September 2023 (EMA).
Scope
M7 applies to new drug substances and new drug products, both during clinical development and in marketing applications. For products already on the market, it applies to post-approval changes such as (ICH M7(R2) guideline):
- a change to the synthesis that brings in new impurities or raises acceptance criteria
- a formulation or process change that creates new degradation products
- a change in indication or dosing that significantly affects the acceptable cancer risk
It is not applied retrospectively to products marketed before it was adopted.
M7 is not intended for biological and biotechnological products, peptides, oligonucleotides, radiopharmaceuticals, fermentation products, herbal products or crude products of animal or plant origin. It also does not apply to drug substances and products for advanced cancer indications as defined in ICH S9. Excipients in existing marketed products, flavourings, colourants and perfumes are out too. Leachables from packaging are outside scope, though you may use its principles (ICH M7(R2) guideline).
Semi-synthetic substances are in scope where manufacturing steps could introduce mutagenic impurities. And an impurity that is carcinogenic but not mutagenic falls outside M7 altogether (M7(R2) Q&As).
Hazard assessment and the five classes
The assessment starts with database and literature searches for carcinogenicity and bacterial mutagenicity (Ames) data. Where no data exist, you run a (Q)SAR assessment with two complementary methods: one expert rule-based, one statistical. Both must follow OECD validation principles. If neither finds a structural alert, that is enough to conclude there is no mutagenic concern (ICH M7(R2) guideline). An out-of-domain result from one model doesn't get you to Class 5 on its own. It needs expert review. Table 1 of the guideline defines five classes:
| Class | What it means | Control |
|---|---|---|
| 1 | Known mutagenic carcinogen | At or below a compound-specific limit |
| 2 | Known mutagen, carcinogenic potential unknown | At or below the TTC-based limit |
| 3 | Alerting structure unrelated to the drug substance, no mutagenicity data | At the TTC, or run an Ames test (negative goes to Class 5, positive to Class 2) |
| 4 | Alerting structure shared with the drug substance or related compounds that tested non-mutagenic | Treat as non-mutagenic impurity |
| 5 | No structural alert, or enough data showing no mutagenicity or carcinogenicity | Treat as non-mutagenic impurity |
An Ames-negative but clastogenic impurity is also Class 5 for M7 purposes (M7(R2) Q&As).
Acceptable intake limits
The TTC of 1.5 µg/person/day matches a theoretical excess lifetime cancer risk below 1 in 100,000. It applies to Class 2 and Class 3 impurities. Class 1 impurities get a compound-specific limit, by default calculated from the TD50 by linear extrapolation (ICH M7(R2) guideline).
Shorter treatment allows higher daily intakes. Tables 2 and 3 of the ICH guideline set conservative duration-based limits:
| Treatment duration | One impurity (µg/day) | Total, 3 or more Class 2/3 impurities (µg/day) |
|---|---|---|
| ≤ 1 month | 120 | 120 |
| > 1 to 12 months | 20 | 60 |
| > 1 to 10 years | 10 | 30 |
| > 10 years to lifetime | 1.5 | 5 |
The total limit applies only when three or more Class 2 or 3 impurities are specified on the drug substance specification. With two, only the individual limits apply. Class 1 impurities and degradation products in the drug product are left out of the total (ICH M7(R2) guideline).
For intermittent dosing, count the total dosing days. Weekly dosing for 2 years is 104 days, which allows 20 µg per dose. A compound-specific intake can be scaled for a shorter course in the same proportions. Use the lower of that scaled value and 0.5% of the daily dose, which is 500 µg for a 100 mg/day drug (ICH M7(R2) guideline). This less-than-lifetime (LTL) adjustment applies to TTC limits and to compound- or class-specific intakes. It does not apply to PDEs (M7(R2) Q&As).
The Addendum holds 21 compound monographs, 14 from R1 and 7 added in R2. Most acceptable intakes come from TD50 linear extrapolation, for example acrylonitrile at 6 µg/day, benzyl chloride at 41 and bis(chloromethyl)ether at 0.004. Aniline (720 µg/day) and hydrogen peroxide (68,000 µg/day or 0.5%) get PDEs instead, because a non-mutagenic mode of action was shown. Dimethyl sulfate defaults to the 1.5 µg/day TTC.
Control options
Section 8.1 of the guideline gives four ways to show control:
- Test for the impurity in the drug substance specification, with an acceptance criterion at or below the acceptable limit. Periodic (skip) testing is possible if levels stay below 30% of the limit in at least 6 consecutive pilot-scale or 3 consecutive production-scale batches.
- Test in a raw material, starting material or intermediate, or as an in-process control, at or below the acceptable limit.
- Test upstream with a higher acceptance criterion, backed by fate and purge understanding and process controls that keep the drug substance below the limit.
- Rely on process understanding and purge, with no analytical testing (ICH M7(R2) guideline).
After approval, new Class 1 or 2 hazard data, or a newly found Class 1, Class 2 or cohort-of-concern impurity, triggers re-evaluation (ICH M7(R2) guideline).
Nitrosamine impurities under ICH M7
M7 does not set nitrosamine limits. It puts N-nitroso compounds in a "cohort of concern" with aflatoxin-like and alkyl-azoxy compounds. These are potent enough that intakes even below the TTC could carry a significant cancer risk, so their acceptable intakes "would likely be significantly lower" and should usually be justified case by case (Section 7.5). For marketed products, a structural alert alone does not trigger follow-up unless the structure is in this cohort (ICH M7(R2) guideline). The Addendum has no nitrosamine monograph.
The numbers for carcinogenic nitrosamines come from regulators. The FDA nitrosamine guidance, Control of Nitrosamine Impurities in Human Drugs, was last revised in September 2024. Its separate NDSRI guidance from August 2023 sets out the Carcinogenic Potency Categorization Approach (CPCA) (FDA NDSRI guidance). EMA uses its own CPCA (EMA Appendix 2). The category limits differ: Category 1 is 26.5 ng/day under FDA guidance and 18 ng/day under EMA guidance. Both give 100 ng/day for Category 2, 400 for Category 3 and 1,500 for Categories 4 and 5.
For the two best-known nitrosamines, both agencies use NDMA 96 ng/day and NDEA 26.5 ng/day (FDA CDER limits, EMA Q&A Rev.23). EMA keeps its list of established limits in Appendix 1, Rev.14 as of 13 October 2026 (EMA nitrosamine guidance).
On 24 September 2026 the FDA allowed LTL adjustment for nitrosamines where appropriate. The factors are 80x for ≤1 month, 13.3x for >1 to 12 months, 6.67x for >1 to 10 years and none beyond 10 years (FDA). The CDER limits page also lists 1 August 2027 as an estimated reassessment date for some interim limits (FDA CDER limits). That date applies to the listed limits only. It is not a general extension of the NDSRI deadline.
ICH is now writing a nitrosamine addendum meant to become M7(R3) (concept paper). The February 2026 work plan targets Step 2 in August 2028 and Step 4 in March 2030 (ICH work plan). These are target dates, not adopted requirements. Use the current regional guidance for nitrosamine limits.
Where M7 sits next to Q3A, Q3B, Q3C and Q3D
ICH Q3A and Q3B cover impurities generally and say little about mutagenic ones. Meeting their thresholds does not show a mutagenic impurity is under control (FDA M7(R2) guidance). The sibling guidelines in short:
- ICH Q3A(R2) (2006), impurities in new drug substances. At a maximum daily dose of 2 g or less, the identification threshold is 0.10% or 1.0 mg/day, whichever is lower.
- ICH Q3B(R2) (2006), degradation products in new drug products, with dose-dependent thresholds.
- ICH Q3C(R9) (January 2024), residual solvents. Class 1 solvents should be avoided, Class 2 are limited by solvent-specific PDEs and Class 3 are acceptable at 50 mg/day without justification.
- ICH Q3D(R2) (April 2022), elemental impurities. Class 1 is arsenic, cadmium, mercury and lead.
ICH lists Q3C(R10) and Q3D(R3) as maintenance work, but Q3C(R9) and Q3D(R2) remain the adopted versions (ICH quality guidelines).
You can ask RegAffairs AI what ICH M7 says about a specific impurity and open the cited documents.