Peptides are not illegal -- so it is up to the company/lab doing the testing if they will accept samples from individuals or not; but there is nothing illegal about possession of peptides or many research chems. You can use them for research -- hence the name "research chemicals;" however, using them on humans, or maybe even animals in some cases, for your research is illegal. These are NOT controlled substances.
On a side note:
Some of us have sent out controlled substances such as AAS to be analyzed by accredited labs overseas -- but yes, it does shake your nerves when they ask too many questions at the post office. Controlled substances are a serious rick.