Consent to clinical research - Adequately voluntary or substantially influenced?

In clinical research the giving of consent by the patient often lies within the context of illness or the doctor/patient relationship. On exploration of these issues it would appear unlikely that the patient's consent is free of substantial differences, some of which may be strong enough to be controlling. Five categories of consent are suggested: voluntary, involuntary, coerced, enforced and partially voluntary. It is argued that consent in clinical research is substantially influenced and thus only partially voluntary. Several practical strategies are proposed to ensure adequately voluntary consent by reducing some circumstantial influences when consent to clinical research is obtained.