As with all areas of medicine, psychologists accept and endorse a set of standards, including ethical guidelines, that are designed at least in part to protect the interests of the patient or of the research subject.
The first and foremost ethical or moral standard under which psychologists, as with all other practitioners of medicine, abide is encompassed in the Latin phrase "primum non nocere," which translates as "first, do no harm," which was derived from the Hippocratic Oath ("...I will do no harm or injustice...").
Psychologists conducting research on living subjects have a moral obligation to protect those subjects from harm. When studying the effects of external stimuli on research subjects, for example, the reactions of human subjects to images intended to evoke terror, sorrow, joy, etc., it is encumbant upon the researcher to ensure that no permanent or enduring emotional damage results from the experimentation. Similarly, research involving animals, for example, primates or rodents, is expected to include protections for those animals from physical harm.
In addition to the ethical or moral requirement to prevent harm to the patient or research subject, psychologists are required to protect the confidentiality of the the patient or subject's personal history and information. Breaches of confidentiality are excused under extenuating circumstances, for example, to protect someone from physical harm, but confidentiality is a cornerstone of the practice of psychology.
The American Psychological Association includes in its "code of conduct" for psychologists its list of "general principles," which include the expectation that those conducting experiments or providing treatment "seek to safeguard the welfare and rights of those with whom they interact professionally and other affected persons and the welfare of animal subjects of resarch." Additionally, psychologists are expected to "respect the dignity and worth of all people, and the rights of individuals to privacy, confidentiality, and self-determination."
In short, psychologists are expected to conduct themselves with high regard for the subjects of their experiments and for their patients.