Ketamine and nitrous oxide are being used to help treat depression in new clinical trials in Australia.
Researchers believe the drugs, which are commonly dealt on the black market, can act as antidepressants.
Nitrous oxide, the chemical inside whipped cream canisters known to some as "nangs", has already shown promise as a rapid antidepressant and could be used to treat acutely suicidal patients.
The treatment would not be delivered through a canister, but in a clinical setting through a mask.
Ketamine, a horse tranquilliser that can cause psychedelic effects in humans, is being investigated by the University of NSW to determine if the drug will work as a long-term therapy for depression and "improve anxiety, suicidal ideation and health-related quality of life".