What are the limitations of using Informed Consent in a study? And how do researchers overcome this?

Limitations:- If a participant is given information concerning the nature and purpose of a study this may invalidate the purpose of the study.- Even if researchers have sought and obtained informed consent, that does not guarantee that participants really do understand what they have let themselves in for. - The problem with presumptive consent (see the explanation of this term below) is that what people expect that they will or will not mind can be different from actually experiencing it. (E.g. Milgram’s Study)Overcoming Limitations:- Participants are asked to formally indicate their agreement to participate and this should be based on comprehensive information concerning the nature and purpose of the research and their role in it.- An alternative is to gain presumptive consent: A method of dealing with lack of informed consent or deception, by asking a group of people who are similar to the participants whether they would agree to take part in a study. If this group of people consents to the procedures in the proposed study, it is presumed that the real participants would also have agreed.- Researchers can also offer the right to withdraw.