Untested drugs can be used to treat patients infected with the Ebola virus, the World Health Organization says.
The WHO said it was ethical in light of the scale of the outbreak and high number of deaths – more than 1,000 people have died in West Africa.
The statement was made after its medical experts met in Switzerland on Monday to discuss the issue.
But officials warned there were very limited supplies of potential treatments.
Dr Marie-Paule Kieny from the WHO said that there has been “unanimous agreement” among experts
The WHO said where experimental treatments are used there must be informed consent and the results of the treatment collected and shared.
In a statement, it said: “In the particular circumstances of this outbreak, and provided certain conditions are met, the panel reached consensus that it is ethical to offer unproven interventions with as yet unknown efficacy and adverse effects, as potential treatment or prevention.”
But the organisation conceded there were still many questions to be answered including how data could be gathered effectively while the focus remained on providing good medical care.
It was also unclear where the funding for the treatment would come from.
Last week the WHO declared the Ebola outbreak was a global health emergency.
But the WHO said there were only 12 doses.
Zmapp has been used on two US aid workers who have shown signs of improvement, although it is not certain what role the medication played in this.
A Roman Catholic priest, infected with Ebola in Liberia, who died after returning home to Spain is also thought to have been given the drug.
However, the drug has only been tested on monkeys and has not yet been evaluated for safety in humans.