Because the CYP3A4 isoenzyme plays a major role in the metabolism of methadone, drugs that inhibit CYP3A4 activity may cause decreased clearance of methadone which could lead to an increase in methadone plasma concentrations and result in increased or prolonged opioid effects. These effects could be more pronounced with concomitant use of CYP 2C9 and 3A4 inhibitors. If co-administration with methadone hydrochloride tablets is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider dose adjustments until stable drug effects are achieved [see Clinical Pharmacology () ] .
There are five primary color-tests reagents used for general screening purposes. The Marquis reagent turns into a variety of colors when in the presence of different substances. Dille-Koppanyi reagent uses two chemical solutions which turns a violet-blue color in the presence of barbiturates. Duquenois-Levine reagent is a series of chemical solutions that turn to the color of purple when the vegetation of marijuana is added. Van Urk reagent turns blue-purple when in the presence of LSD. Scott Test's chemical solution shows up as a faint blue for cocaine base. 
Safety during pregnancy has not been established. Methadone has been shown to cross the placenta, and it is found in cord blood, amniotic fluid and in the newborn urine. Children born to mothers who were taking methadone for a prolonged period may exhibit respiratory depression or withdrawal symptoms. Methadone enters breast milk, and this can cause sedation and respiratory depression in the breast feeding infant. The benefit to the mother of taking methadone while breast feeding should be weighed against the risks to the infant.