Cocaine itself is metabolized too rapidly to be detected in the urine. Opiates are a class of drugs including morphine, heroin and opium. Some over the counter diet products and cold medications fall into this class, and will be detected. Methadone is a drug used in substance abuse treatment programs. It is a narcotic, like the opiates, and is sometimes sold by addicts undergoing treatment - therefore subject to abuse.
Benzodiazepines are effective in treating anxiety and sleep disorders.
Barbiturates are used as anticonvulsants and in management of migranes. Many substances, including prescription drugs or drug metabolites, may cross react in the drug screen. In a cross-reaction, a compound not being tested reacts in the analysis as if it were the drug or metabolite being tested, creating a false positive. Often, a cross-reactant has a similar chemical structure to the drug or metabolite being tested. Always try to determine medications, prescription or over the counter, recently used by the donor.