Hi There. Can You Please Assist. My Husband And I

Hi there. Can you please assist. My husband and I are 44yrs old and don't do drugs. He actually tested positive to a road side swab for methylamphetamine.? we are really confused to why. The only thing we can think contributed may have been a prescription Duromine that is actually mine that he took or he also took a pill for intergestion as he had had the sleeve(weight loss surgery). Can you please advise whether any of these may have contributed to a positive reading. Thankyou so much