Why are they hazardous?

Most controlled drugs are classified as hazardous substances. For example, according to safety data sheets, diamorphine (heroin) and amphetamine are extremely toxic whilst cocaine is moderately toxic and suspected of damaging fertility or the unborn child. Historic drugs may also have toxic additives such as lead, arsenic, mercury and strychnine. It is generally thought that historic drugs have not lost any of their potency and should be presumed to be hazardous.