I am on pain mgmt medications, so my doctor drug tests me when I see him. It is routine and NOT because he suspects anything. He has to do it in order to be able to rx medications for me. A few years ago I had a long migraine (weeks long) and could not keep medications down for over a week of that. I was on an antiseizure medication to try to prevent migraines and for nerve pain (one medication, 2 reasons). Going off cold turkey because the migraine caused me to have a very long, very bad seizure. I ended up in the hospital. The hospital drug test showed a LOT of things including a high meth level. I have NEVER even seen meth or most illegal drugs. I saw pot back when I worked in a certain restaurant, but that is about it.
After I got out of the hospital, my doctor was angry because they didn't call him. He knows a TON more about drug tests than the hospital docs, and the way the hospital lab did the tests caused the anti-nausea medication I was on (with an rx) to show up as meth. It is a COMMON false positive and ANY doctor/lab should know it. But in our hospital there are no false positives. They even threatened to take my kdis awya if I didn't get treatment - a letter from my doctor solved that and took the false positive report from my hospital records.
the reason the lab wants a "do over" for the test is because it is COMMON for people to drink large amts of water to dilute any mj in their system. If someone does not seem to be serious about treatment, they look at these things and often want confirmation. They have limited space in threatment and a lot of people wanting in for various reasons. The rules are not set up to be against your difficult child, but because they KNOW what addicts do, and addicts lie. they just do - it is a sx of addiction. They also know the various tricks that are used to get clean results if you are using. The other thing that has them re-do watered down tests is that there are people who sell their clean urine to addicts. If they have several addicts wanting their urine, they will add water to the urine to have more to sell. Or to water their own down if they have used so that their clients won't come after them furious because they popped clean after buying "clean" urine. I have had people ask to buy mine, bakc when I worked at that restaurant. I have also heard of people actually taking it out of a toilet after someone who they think is clean has used the toilet. Yes, that is gross, but I heard someone at a family day session at rehab say that they had done this quite often when people forgot to flush.
Having had SO MANY people try all of these things, and lie to them in so many ways, treatment centers just don't trust. they can't be trusting and still be effective in doing their jobs. It is NOT personal or wanting your son to fail. Your son has a disease that causes him to lie, and he is going to have to do a LOT mroe than just redo a drug test to prove that he is clean and wants recovery. It is a natural consequence of the disease. How helpful would the treatment place be if they accepted every excuse/reason for test results being off or someone behaving or seeming high or hungover or whatever? They want their clients to succeed, but they MUST verify everything the addict says because otherwise they would be failing their clients.