London police are warning residents after multiple incidents of suspicious packages being received at homes in the city.

Const. Ricardo Julio says “There is no immediate danger in terms of to the public with the stuff that we found so far in the envelopes. That’s not to say things will change and we do find envelopes with something that is harmful to people. So that’s why we’re putting out into the public to let them know if they do find a package like this in their mail, don’t open it. Call us right away.”

Investigators say some residents have received envelopes in the mail marked ‘Return to Sender’ that they did not send.

The envelopes appear to have initially been sent to an address in the U.S., usually with insufficient postage and showing a return address in London.

Police say the envelopes were found to contain “blank paper with a prepared package of anti-anxiety medication,” but the envelope and medication package are not commercial.

Officials are hoping to examine any other similar packages received by the public with a U.S. address and marked ‘Return to Sender.’

Anyone with information or who receives a package should not open it and call London police at 519-661-5670.