Investigations are currently ongoing. The EMA advises patients in the EU to continue to take metformin medication as the risks from not treating diabetes far outweigh any possible effects of the low levels of NDMA seen in tests.

New reports on the topic issued by the US FDA and Swissmedic:

In the US, various manufacturers have already voluntarily recalled their extended release (ER) metformin products in July 2020. The last voluntary recalls go back to 5 October 2020. Still, the FDA also recommends patients to continue taking their usual ER metformin. The agency’s testing has not shown NDMA in the most commonly prescribed type of metformin products.

On 22 October 2020, the Swiss national authority Swissmedic reported traces of the nitrosamine MeNP (1-nitroso-4-methylpiperazine) in tuberculosis drugs containing rifampicin. They were detected in batches of active substances and finished products on the Swiss market.
Swissmedic has set a temporary limit for MeNP. As is further reported, Swissmedic has passed on the results obtained in the laboratory to partner institutions such as the EDQM (OMCL network) and the EMA. Further risk assessments are being carried out together with partner authorities and marketing authorisation holders.

Sources:

EMA: Metformin-containing medicines

FDA: Recall of extended release (ER) metformin

Swissmedic: News