Methoxyflurane

Methoxyflurane (brand name: Penthrox) is an Australian liquid analgesic (a painkiller) which turns into a gas when it is exposed to the air.
It is breathed in through a special inhaler which is known in some places as the "Big Green Whistle". It makes a slight whistling noise when the patient breathes through it.
The patient takes the medicine themselves in the presence of someone trained in its use. It can make them feel sick (nausea) or cause them to be sick (vomit). It also causes dizziness.