Hydrolyzes N(G),N(G)-dimethyl-L-arginine (ADMA) and N(G)- monomethyl-L-arginine (MMA) which act as inhibitors of NOS. Has therefore a role in the regulation of nitric oxide generation. {ECO:0000269|PubMed:18171027, ECO:0000269|PubMed:19663506, ECO:0000269|PubMed:21493890, ECO:0000269|PubMed:37296100}. This is the function of DDAH1 (dimethylarginine dimethylaminohydrolase 1, ENSG00000153904).