I think my son has got into my flexeril but I'm not sure, can it be used for subtance abuse?

This drug can cause sedation and could be misused for that effect. Generally when people start taking Flexeril they are very sleepy so I would watch for excessive sleepiness (but that's a little difficult in a teen since they sleep a lot anyway) but watch for excessive daytime sleepiness, possibly slurred speech. Be sure you keep your pills away from an easy access area. If you are keeping them in a common room of the house like a bathroom or kitchen cabinet, it could be anyone who comes into your house who may "borrow" a few! Keep them in an area that isnt easily accessed by anyone coming in the house. I keep my meds in my bedroom and I also keep count of my meds pretty frequently so I can be alerted to the possibility of someone else accessing my meds. I have had instances of missing a few and I'm pretty sure it was a certain friend of my sons who has admitted prescription drug use to my son before and the instances of missing pills came up twice after this certain boy had been to my house. It was after that last instance I started keeping them in a drawer in my bedroom or in a pocket of a jacket inside my bedroom closet so they are not easily found by anyone. If you do suspect your son is taking them then the best thing to do is ask him. When it happened to me I just asked my son about it in a non accusatory way. He said he didnt take them and I did believe him. He had mentioned that the certain boy I talked about had been to the house but we were not sure at that time if he was the culprit, then it happened again after this boy had visited so we were pretty sure at this point but I dont have absolute proof so I just keep them hidden now and I change up hiding spots every so often and keep count and since I started doing this I've had no further problems. Keep in mind that it could be anyone if they are kept in a common area of the house. Good Luck!