It is illegal, however some labs have very good stealth when it comes to identifying people, it's like apple not unlocking potential terrorists phones, everyone has the right to privacy. I went to a festival and there was a centre on-site, you could turn anything in (I just found a half-bag of white powder), they'd take a tiny bit give it you back, take your phone number and text you with the results! I've never had an issue but like everything it's possible