What Happens When a Participant’s Decision-Making Capacity Fluctuates During a Long Study?

What If a Participant Can Consent on Some Days but Not Others?

Not every change in decision-making capacity follows a simple path from “has capacity” to “has permanently lost capacity.” Some participants experience periods in which they can understand and make a research decision, followed by periods in which illness, medication, delirium, cognitive impairment, psychiatric symptoms, fatigue, or another condition interferes with that ability.

This creates a difficult problem in long studies. Whose decision governs participation when capacity changes over time? Should consent be reassessed at every visit? Can a legally authorized representative make decisions during periods of impairment? What happens when the participant later regains capacity?

The answer requires something more responsive than a one-time capacity determination. When fluctuation is foreseeable or becomes apparent, the consent process should adapt to the participant's current ability to make the relevant decision.

Consent Authority May Need to Change as Capacity Changes

Capacity Can Change, So Consent Procedures Sometimes Need to Change With It

Capacity Is Not Always Stable

SACHRP specifically cautions against treating consent capacity as simply present or absent. It describes capacity as occurring along a continuum and notes that impairment may improve, fluctuate, or worsen during research as the participant's underlying condition changes.

This is particularly relevant to longitudinal studies. A participant who provided valid consent at enrollment may later experience a period of impairment and subsequently recover sufficient ability to make their own decisions again.

The appropriate response is therefore not to assign the participant permanently to a “capable” or “incapable” category after one assessment.

Capacity Is Also Decision-Specific

A person may have sufficient capacity for one research decision but not another. The complexity and consequences of the decision matter.

For example, understanding whether to complete a brief low-risk questionnaire may require a different level of decision-making ability from deciding whether to undergo an invasive experimental procedure with substantial uncertainty. SACHRP recommends tailoring assessment methods to the population, study risk, and likelihood of impaired consent capacity.

Do Not Confuse a Decision You Dislike With Loss of Capacity

A participant who once wanted to continue may later refuse. Another who previously refused an optional procedure may later accept it. Neither change necessarily indicates fluctuating capacity.

Capacity concerns should arise from the participant's ability to understand and use information relevant to the decision, not from whether their decision is consistent with what researchers, family members, or representatives would prefer.

Reassessment Should Be Triggered by the Study and the Participant, Not Ritual Alone

SACHRP recommends considering safeguards throughout participation when impaired capacity is anticipated and states that requirements for reassessment and reconsent should reflect the circumstances. More intensive capacity assessments can burden participants and researchers, so they should be proportionate to the likelihood of impairment and the risks involved.

This means there is no universal rule that every longitudinal study should administer a formal capacity instrument at every visit. Some studies may appropriately use scheduled reassessment because fluctuation is highly foreseeable. Others may rely on routine interaction unless a change raises a genuine concern.

Timing Can Sometimes Protect Autonomy

When fluctuations follow a reasonably predictable pattern, researchers may sometimes be able to schedule non-urgent consent discussions or research decisions during periods when the participant is more capable of engaging with the information.

This should not become manipulation of timing to obtain the answer researchers want. Rather, when scientifically and clinically appropriate, choosing a time when the participant is best able to understand and decide can support autonomy.

If a research procedure cannot safely or validly wait, the protocol and applicable authorization pathway determine what happens during a period of incapacity.

A Legally Authorized Representative Does Not Permanently Replace the Participant

During a period in which the participant lacks sufficient capacity, a legally authorized representative may be able to provide authorization if the study, applicable law, and ethics approval permit it. The representative's role can include ongoing research decisions rather than merely the initial enrollment decision.

But that authority should not be treated as permanent merely because it was needed once. OHRP states that if a participant regains capacity, their own consent must be obtained for further research because consent from the legally authorized representative is no longer the appropriate substitute.

This creates a dynamic arrangement: participant consent when capacity is sufficient, representative authorization when legally appropriate during incapacity, and return of decision-making to the participant when capacity returns.

The Participant Should Remain Part of the Conversation During Impairment

Even when a participant cannot provide legally effective informed consent, they may retain substantial ability to understand simplified information, express preferences, ask questions, cooperate, refuse, or indicate distress.

SACHRP recommends involving participants with impaired consent capacity to the extent possible and seeking assent when appropriate. It also recommends considering dissent, including nonverbal indications that a person does not want to take part in a procedure.

The ethical goal is not to transfer the participant's voice to a representative at the first sign of impairment. It is to preserve as much meaningful self-determination as the participant's current abilities permit.

Fluctuation Makes Advance Planning Particularly Valuable

When researchers reasonably expect capacity to change, the original consent process can include discussion of what should happen if the participant later becomes unable to decide. OHRP specifically recommends considering whether prospective participants in longitudinal studies involving progressive or intermittent impairment should designate someone who could serve as a legally authorized representative, consistent with applicable law.

Researchers can also plan how capacity will be reassessed, which decisions require reassessment, how participant assent and dissent will be handled, and what happens if capacity returns.

Do Not Turn Every Moment of Confusion Into a Capacity Determination

A tired participant forgetting an appointment detail does not necessarily require formal capacity assessment. Neither does asking the same question twice. Ordinary memory lapses, anxiety, language barriers, sensory impairment, unfamiliar terminology, or poor explanation can all interfere with communication without eliminating decision-making capacity.

Before escalating, researchers should consider whether clearer explanation or another communication accommodation resolves the difficulty. The distinction between fluctuating capacity and forgetting what was previously explained can be particularly important in long studies.

Permanent Loss and Fluctuating Capacity Require Different Planning

If assessment indicates that the participant has lost capacity and recovery is not currently expected, the study may move into the procedures established for continuing research with a participant who cannot consent. With fluctuation, however, researchers should remain alert to periods in which the participant can once again make the decision personally.

The question of whether research data collection can continue after loss of capacity therefore becomes one part of a larger cycle when capacity repeatedly changes.

When Capacity Changes Between Study Visits

The important feature is not simply that capacity was reassessed. Decision-making authority followed the participant's actual ability rather than being permanently assigned based on one earlier period of impairment.

Common Mistakes About Fluctuating Consent Capacity

Build a Consent Process That Can Respond to Change

Studies involving foreseeable fluctuations should establish a plan before the first fluctuation occurs. That plan should make clear how concerns are recognized, when capacity is reassessed, who may provide authorization during incapacity, and how decision-making returns to the participant.

The broader principle remains that consent must remain responsive throughout participation. Fluctuating capacity makes that principle unusually visible because the person authorized to make the decision may legitimately change over time.

When Consent Capacity May Fluctuate

Questions About Fluctuating Capacity During Research

Decision-Making Authority Should Respond to the Participant's Current Capacity

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