Cold sores are caused by the herpes simplex type 1 virus and are contagious whereas canker sores are not. Also, cold sores can appear outside the mouth in places such as under the nose, on the lips or under the chin while canker sores always appear inside the mouth.anker sores, or aphthous stomatitis, are small ulcers in your mouth that cause pain and discomfort when talking or eating. Canker sores come in two varieties: simple and complex.
Codeine, which is found in many pain relievers, may cause a false positive for morphine or heroin because of its similar chemical structure. Antibiotics. Certain newly developed antibiotics including amoxicillin and ampicillin have been reported to cause false positives for cocaine. DHEA
Phenylpropanolamine and ephedrine are both substances found in many over-the-counter cold remedies. They can result in a drug test false positive for amphetamines on the EMIT test. Antitussives, to suppress coughs, such as dextromethorphan and perylamine may cause a drug test false positive for opiates.rug Testing â False Positives. In drug testing, a false positive is defined as a drug free sample falsely being reported as showing positive for drugs. This can occur for a number of reasons including: improper laboratory procedure, mixing up samples, incorrect paperwork and passive inhalation.