Hi there and thank you for your question. I can understand that this is a concerning situation for you as your son s history doesn t make sense with a positive THC test. The good news is that there are indeed two main classes of medications that can cause false positive results regarding THC. These are your non-steroidal anti-inflammatories (NSAIDS) such as ibuprofen and naproxen and your proton pump inhibitors (PPI) such as omeprazole, pantoprazole, etc. NSAIDS are commonly used for pain, fever and swelling and PPI s are used to reduce acid production in the stomach for patients suffering from acid reflux. You mentioned that he was struggling with a cold so he may have used medication that contains ibuprofen in it. The only issue you may run into is that these tests have been developed to be as precise as possible and to exclude as many false positive results as possible. I would suggest speaking to your son to try and exclude those medications, if he has used them, for about a week and then repeat the toxicology screen. If it still comes up positive for THC then you ll need to speak to him and just remind him that you re his mother and that he knows he can trust you and you won t be upset with him. Just to play devil s advocate, if he did use marijuana, he may just be embarrassed to tell you and feel that he s taken advantage of your trust and he s upset with himself now. I hope this helps you and good luck.