When Your Person Can't Consent: Legal and Ethical Considerations for Trial Enrollment

Most of what you read about clinical trials assumes the participant can read the consent form, ask questions, and sign their own name. But Parkinson's can, for some people, affect thinking and decision-making, especially in its later stages or when dementia is part of the picture. So a fair and difficult question comes up: if your person can no longer consent for themselves, can they still take part in research at all?

The short answer is: sometimes, and only with serious safeguards. This article explains how that works and the ethics behind it. It is general information, not legal advice, and the specifics depend heavily on the study, the institution, and the law where your person lives.

What "Capacity to Consent" Actually Means

Capacity is the ability to understand a decision, weigh its risks and benefits, and communicate a choice. It is not all-or-nothing, and it is not the same as a diagnosis. Someone with cognitive changes may still have the capacity to make some decisions, and capacity can vary day to day. In research, the study team formally assesses whether a potential participant can understand what they are agreeing to.

If a person is found to lack the capacity to consent to a particular study, that does not automatically end the conversation, but it does change who decides and how.

The Legally Authorized Representative

When someone cannot consent for themselves, research may still be possible through a legally authorized representative (LAR). This is the person permitted to make research decisions on another's behalf. Who qualifies as an LAR is defined by the institution's ethics board, the Institutional Review Board (IRB), and by local law, so it varies. It is frequently the same person named in a durable healthcare power of attorney, which is one more reason to set that document up early. We cover the paperwork in our guide on power of attorney and advance directives.

Consent, Assent, and the Right to Refuse

Ethical research draws a careful line between two ideas:

• Consent is the formal, legally recognized agreement to take part, which an LAR may provide when the person cannot.
• Assent is your person's own willingness to participate, sought even when they cannot give legally valid consent.

This distinction matters enormously. Even when a representative has agreed, the participant's own objection is respected. If your person pulls away, says no, or is distressed by a procedure, that refusal carries weight regardless of any signature. The goal is never to enroll someone against their evident wishes; it is to let them benefit from research they would plausibly have wanted, with protection at every step.

The Safeguards That Protect Participants

Research involving people who cannot consent is held to a higher standard, not a lower one. Every legitimate study is reviewed by an IRB or ethics committee whose job is to weigh whether the potential benefit justifies the risk, especially for participants who cannot speak for themselves. Studies that enroll people with impaired capacity typically must show that the research needs this population (you cannot answer a dementia question by studying only people without it) and that risks are minimized. You can read the official registry entry for any study, including its eligibility and oversight, on ClinicalTrials.gov.

Questions Worth Asking the Study Team

If you are weighing a trial for a person who may lack full capacity, these questions cut to what matters:

• Does this study allow enrollment through a legally authorized representative, and do I qualify?
• How will the team assess my person's assent, and what happens if they object?
• What are the specific risks, and how does the study minimize them?
• Can my person be withdrawn at any time, and how?
• Has this been reviewed by an ethics board, and who do I contact with concerns?

Holding Two Things at Once

Families in this situation are often pulled between two honest impulses: the hope that research might help, and the duty to protect someone who can no longer fully protect themselves. You do not have to resolve that tension alone. The study team, the ethics board, and your person's own neurologist are all part of the decision. And the most important safeguard of all is the one you already carry: knowing your person well enough to recognize what they would have wanted, and to notice immediately if something is wrong. Our companion guide on your role during a clinical trial covers that day-to-day watchfulness.