Declaration of Helsinki

https://www.who.int/bulletin/archives/79%284%29373.pdf

Article 32 – last one
In the treatment of a patient, where proven prophylactic, diagnostic and therapeutic methods do not exist or have been ineffective, the physician, with informed consent
from the patient, must be free to use unproven or new prophylactic, diagnostic and therapeutic measures, if in the physician’s judgement it offers hope of saving life, reestablishing health or alleviating suffering.
Where possible, these measures should be made the object of research, designed to evaluate their safety and efficacy. In all cases, new information should be recorded and, where appropriate, published.
The other relevant guidelines of this Declaration should be followed.