Heroin is an opiod agonist. It's is a semi-synthetic drug which is derived from opium, and has the chemical formula C21H23NO3. Opium is produced by the opium poppy - papaver somniferum. The group of opiod agonists includes many other drugs, one is morphine, the direct derivative of opium. There are semi synthetics that are also derived from opium, heroin is one, along with codeine and dilaudid; and many fully synthetic drugs which act upon the same parts of the brain, like pethidine, methadone, and LAAM.