The term opiate refers to the alkaloids found in opium, an extract from the unripe seeds of the opium poppy (Papaver somniferum L.). It has also traditionally referred to natural and semi-synthetic derivatives of morphine. The term is often incorrectly used to refer to all drugs with opium-/morphine-like pharmacological action, which are more properly classified under the broader term opioid.
The main opiates from opium are morphine, codeine and thebaine. Papaverine is also present, but has essentially no effect on the central nervous system, so is not an opioid.
See opioid for a fuller discussion.