The Statistical Magic Trick: How Trials Share Results While Staying Blind

 

In the world of clinical research, "breaking the blind" is typically a cardinal sin. Yet, high-stakes Phase 3 trials like ORIGIN 3 (atacicept), PROTECT (sparsentan), and ATTRIBUTE-CM (acoramidis) have all successfully navigated the complex path of publishing interim results in the New England Journal of Medicine while keeping their long-term studies scientifically intact.

• Lafayette et al (2026) A Phase 3 Trial of Atacicept in Patients with IgA Nephropathy
• Perkovic et al (2026) Sibeprenlimab in IgA Nephropathy — Interim Analysis of a Phase 3 Trial
• Gillmore, et al (2024)Efficacy and Safety of Acoramidis in Transthyretin Amyloid Cardiomyopathy and its attached protocol and statistical analysis plan "

How do they pull off this statistical magic trick? It comes down to a rigorous architectural separation of data and people including statistical analysis team. Here is a look at the techniques used to maintain the "blind" during interim disclosures.

1. The "Firewall" Strategy: Independent Reporting Teams

The most critical technique used across all three studies is the creation of a "Firewall."

While a trial is ongoing, the people running the study (Sponsor clinical teams, investigators at hospitals, and the patients) must remain blinded. To perform an interim analysis, the Sponsor appoints an Independent Reporting Team (IRT) or an Independent Statistical Center.

• How it works: This group has no contact with the study sites. They receive the raw "unblinded" data, perform the calculations for the primary endpoint (like the 36-week proteinuria reduction in PROTECT or ORIGIN 3), and prepare the manuscript for publication.
• The Result: The people actually treating the patients remain in the dark, ensuring their medical decisions aren't influenced by knowing who is on the "winning" drug.

2. Safeguarding Against "Functional Unblinding"

In some trials, the drug’s effect is so obvious it could accidentally reveal the treatment.

• In ORIGIN 3: Atacicept significantly lowers serum IgA and IgG levels. If a doctor saw these lab results, they would immediately know the patient was on the active drug. To prevent this, these specific lab values are suppressed. The results are sent to the Independent Reporting Team but are hidden from the investigators and the Sponsor’s site monitors.
• In PROTECT: This study compared two active drugs (sparsentan vs. irbesartan). To ensure the difference in pill appearance didn't tip anyone off, they used a Double-Dummy design. Every patient took two sets of pills—one active and one placebo—so the physical routine remained identical for everyone.

3. Aggregate vs. Individual Disclosure

A common misconception is that "publishing the results" means everyone knows who got what. In reality, the NEJM publications for these trials only disclose aggregate data (group averages), not the individual patient level data.

• In ATTRIBUTE-CM: When the Part A results (12-month 6-minute walk distance) were disclosed, the public learned how the group performed. However, the individual treatment assignments for each patient remained locked in the secure database.
• The Benefit: Even if an investigator reads the NEJM article and sees that acoramidis is effective, they still do not know if the specific patient sitting in their office is receiving acoramidis or the placebo.

4. Prespecified Alpha Spending and "The Gatekeeper"

To maintain the statistical integrity of the final results (like the 104-week kidney function in ORIGIN 3 or the 30-month clinical outcomes in ATTRIBUTE-CM), the Statistical Analysis Plan (SAP) dictates exactly how much "statistical credit" is used during the interim look.

• The Independent Data Monitoring Committee (iDMC) acts as the gatekeeper. They review the unblinded data behind closed doors and only allow the trial to proceed if the interim disclosure doesn't compromise the "power" of the final analysis.

Why go through all this trouble?

The goal is Accelerated Approval. By using these techniques, sponsors can show the FDA (and the medical community) that a drug works on a "surrogate marker" (like proteinuria) at an interim stage. This allows life-saving drugs to reach patients years earlier, while the "blinded" portion of the trial continues to gather the long-term data needed for full, traditional approval.

By combining physical dummies, suppressed lab data, and strict "firewalls" between statistical teams, researchers prove that you can indeed share the news of a trial's success without ruining the science that supports it.

Some Extra Words on ATTRIBUTE-CM Study

ATTRIBUTE-CM study is a phase 3, double-blind trial, 632 patients with transthyretin amyloid cardiomyopathy were randomly assigned in a 2:1 ratio to receive acoramidis hydrochloride at a dose of 800 mg twice daily or matching placebo for 30 months. The study contained two parts: Part A with primary endpoint of change from baseline to Month 12 of treatment in distance walked during the 6MWT, Part B with primary endpoint of a hierarchical combination of All-Cause mortality and CV-related hospitalization over a 30month period.

There were two readouts for the study and the Part A readouts were based on an interim analyses by the independent DMC. 

In December 2021, BridgeBio Pharma experienced a major setback when its Phase 3 ATTRibute-CM trial for acoramidis (a treatment for transthyretin amyloid cardiomyopathy - ATTR-CM) failed to meet its primary endpoint of improving the 6-minute walk distance (6MWD) at Month 12 (Part A primary efficacy endpoint). In the initial 12-month data, patients taking acoramidis did not show a statistically significant improvement in their 6MWD compared to those on a placebo.

Despite the failure of the 6MWD endpoint at 12 months, the study continued because the independent data monitoring committee noted encouraging trends in other areas. By July 2023, BridgeBio reported positive top-line results from the full study (Month 30), where acoramidis demonstrated a highly statistically significant improvement in a hierarchical analysis that included mortality, hospitalization, and 6MWD (Part B primary efficacy endpoint). 

Following the successful long-term data (Part B), which showed a 25% reduction in all-cause mortality and 50% reduction in cardiovascular hospitalization frequency (known as Attruby), the drug was approved by the FDA, with 3,751 prescriptions filled as of August 2025.

The study included an embedded Part A readouts that required the unblinding for interim analysis. The sponsor specified the following for maintaining the blinding for the overall study while the Part A results were analyzed and disclosed.

Low-Dose Active-Control Trials in Psychedelic and CNS Drug Development

This week, Compass Pathways plc (Nasdaq: CMPS) announced the successful achievement of the primary endpoint in the ongoing Phase 3 COMP005 trial, the first of two Phase 3 trials evaluating COMP360, a synthetic, proprietary formulation of psilocybin, for treatment-resistant depression (TRD). Psilocybin is a psychedelic drug. The field of psychedelic drug development is experiencing a renaissance, driven by growing interest in their potential to treat mental health disorders including major depression disorder, Post-Traumatic Stress Disorder (PTSD), and advancements in research methodologies. It is interesting to see that the phase 3 study conducted by Compass Pathways plc utilized the clinical trial design with low dose or sub-perceptual dose of the active drug as the control group (versus the traditional placebo as the control group). 

Challenges in Clinical Trial Design for Psychedelic Drug Development

According to FDA guidance "Psychedelic Drugs:Considerations forClinical Investigations", the followings are key challenges for psychedelic drug clincial trials. 

• Functional Unblinding and Expectancy Bias: Psychedelic drugs cause intense perceptual disturbances and alterations in consciousness, making it difficult to maintain blinding in studies. Subjects receiving the active drug often experience "functional unblinding." Additionally, high expectations from participants receiving the active drug, or disappointment (nocebo effect) in those receiving a placebo, can influence outcomes.

• Control Conditions: Using a traditional placebo can be problematic for assessing efficacy due to functional unblinding and the potential for a nocebo effect. While inactive controls help contextualize safety, alternatives like subperceptual doses or other psychoactive drugs are being considered, but they also present their own challenges.

• Contribution of Psychotherapy: Many psychedelic drug development programs incorporate psychological support or psychotherapy. This adds a variable that complicates the assessment of the drug's effectiveness and presents challenges for future product labeling. The specific contribution of the psychotherapy component to any observed efficacy is not yet characterized and has the potential to increase expectancy and performance biases.

• Dose-Response Relationship: The dose-response relationship for most psychedelic drugs is not well understood for both efficacy and safety.

• Durability of Treatment Effect and Repeat Dosing: While current programs explore single or intermittent dosing, many conditions being studied are chronic. Characterizing the durability of response, recommended interdose intervals, and the safety and efficacy of repeat dosing are significant challenges.

• Safety Monitoring During Sessions: Subjects remain in a vulnerable state for up to 12 hours after receiving active treatment. This necessitates specific safety monitoring measures, including observation by two monitors, with a lead monitor who is a healthcare provider with graduate-level training and clinical experience in psychotherapy and is licensed to practice independently.

• Abuse Potential Assessment: Psychedelic drugs act on the central nervous system and produce psychoactive effects, requiring evaluation for abuse potential. This includes monitoring abuse-related adverse events, even if they are hypothesized to be associated with a therapeutic response.

Reagan-Udall Foundation for the FDA organized a workshop "Advancing Psychedelic Clinical Study Design Design", the challenges in psychedelic clinical trial design were extensively discussed:

• Blinding & Expectancy: It's difficult to blind studies due to the profound psychoactive effects, leading to "functional unblinding" where participants and therapists often know who received the active drug. High expectations from media coverage can also inflate outcomes 
• Control Conditions: Traditional placebos can be problematic, leading to unblinding and nocebo effects. Active comparators are an option, but finding one with similar subjective effects without being therapeutic is challenging. Sub-perceptual doses are also being explored, but they might still have psychoactive effects.
• Role of Psychotherapy/Facilitation: The therapeutic intervention (preparation, in-session monitoring, integration) significantly influences outcomes, and its contribution needs to be distinguished from the drug's effect 
• Dose-Response Relationship: Understanding the dose-response relationship for safety and efficacy is crucial, and dose-response trials are considered valuable 
• Durability of Treatment Effect: A major question is how long the effects last and the need for redosing, especially for chronic conditions

One of the approaches to address the blinding issue or functional unblinding issue is to use the low dose (or sub-perceptual dose, sub-optimal dose) of the active drug (in this example, the psychedelic drug psilocybin).  

Low-dose active control is used beyond the psychedelic drug clinical trials. It is also used in other CNS drug clinical trials. Some of the trials with low-dose active control lead to the drug approval by the FDA. Here are examples of Low-Dose Active-Control Trials in CNS Drug Approvals

• Lamotrigine XR (Lamictal XR) – Indication: Conversion to monotherapy for partial-onset seizures in patients ≥13 years. Trial: Study LAM30055 (multicenter conversion-to-monotherapy). Sponsor: GlaxoSmithKline. FDA Approval: April 2011. Reason for design: In epilepsy monotherapy trials, giving a true placebo is unethical. The FDA accepted a “pseudoplacebo” control (historical data from low‐dose valproate) to demonstrate lamotrigine’s efficacy This low-dose VPA arm served as an inferior active control so that a full placebo arm could be avoided while still assessing drug effect.

• Oxcarbazepine (Trileptal) – Indication: Monotherapy for partial-onset seizures. Trial: Two Phase 3 trials comparing high-dose Trileptal (2400 mg/day) to a subtherapeutic Trileptal dose (300 mg/day). Sponsor: Novartis. FDA Approval: mid-2000s (first-line monotherapy around 2005). Reason: Again, placebo was deemed unethical in active seizure patients. The control arm received only 300 mg (a suboptimal dose) of oxcarbazepine. This “low-dose active” control (essentially a pseudo-placebo) allowed demonstration of efficacy (fewer seizures/dropouts in the high-dose arm) without exposing patients to no treatment.

• Pregabalin (Lyrica) – Indication: Monotherapy for partial-onset seizures. Trial: Randomized conversion-to-monotherapy trial of pregabalin 600 mg/day vs pregabalin 150 mg/daypmc.ncbi.nlm.nih.gov (high-dose vs low-dose active control). Sponsor: Pfizer. FDA Approval: ~2017 (supplement to extend indication). Reason: As with other AEDs, full placebo was not used. The trial randomized patients to a high dose or a low “pseudo-placebo” dose (150 mg) of pregabalin. Using a subtherapeutic active dose allowed assessment of efficacy (few patients worsened on 600 mg) while avoiding a true placebo arm. Regulatory briefing notes explain that monotherapy trials in epilepsy often use a “pseudo-placebo” (suboptimal dose of drug) for exactly this ethical reason.

Rationale for Low-Dose Active Controls

These examples share a common rationale: in serious conditions like major depression disorder, PTSD, and epilepsy, withholding effective therapy (i.e. using true placebo) is ethically problematic. Using true placebo results in the functional unblinding. Regulatory authorities have allowed a “low-dose active” or “pseudo-placebo” comparator to ensure trial blinding and assay sensitivity while not denying therapy In practice, patients in the control group receive a sub-therapeutic dose of an anticonvulsant (e.g. low-dose valproate or pregabalin) instead of no drug. This strategy maintains the appearance of treatment, minimizes risk of uncontrolled seizures, and still permits demonstration of dose–response or superiority of the higher dose. As noted in FDA/clinical guidance and literature, this design avoids exposing patients to a completely inert treatment in life‐threatening disorders. In all cases above, the low-dose arm (active control) was chosen for ethical reasons (protecting patients) and to meet regulatory requirements for demonstrating efficacy without a true placebo.

Functional Unblinding in Double-blind, Randomized, Controlled Trials (RCTs)

Earlier this month, FDA advisory committee declined to endorse Lykos Therapeutics’ application to market its psychedelic drug MDNA, also known as ecstasy, as a treatment for post-traumatic stress disorder (PTSD). The panel voted 9-to-2 against the treatment when asked if data showed MDMA’s effectiveness, and 10-to-1 against when asked if the benefits of MDMA outweighed its risks. Both of Lykos Therapeutics’ pivotal studies (MAPP1 study and MAPP2 study) are positive. With relatively small sample sizes, both studies showed highly statistically significant results that MDNA-assisted therapy is highly efficacious in individuals with severe PTSD. The failure in earning the endorsement from FDA advisory committee was not due to the study results, but due to the concerns about the study design and the study conduct, specifically, potential abuse, functional unblinding, and expectation biases. Functional Unblinding was one of the sticky issues discussed during the advisory committee meeting. 

Functional unblinding refers to the situation in a clinical trial or research study where individuals involved (such as participants, investigators, or assessors) gain access to information that reveals the identity of the treatment or intervention being administered. Functional unblinding can happen inadvertently due to various reasons, such as unintended disclosure of treatment details (accidental unblinding), observation of side effects specific to a treatment, or recognition of differences between treatment groups. Clinical trial sponsors usually implement strict procedures to prevent accidental unblinding and manufacture the matched control treatments/using double-dummy technique to prevent recognition of differences between treatment groups. 

However, functional unblinding due to side effects (or treatment emergent adverse events (TEAEs)) may occur with any investigational drug. If the treatment group (or investigational drug) can cause significantly more side effects, study participants, investigators, or assessors can guestimate which treatment group the study participants are assigned to. For example, IGIV causes headache events; niacin causes red or flushed skin, sotatercept causes telangiectasia, bleeding events, and increased hemoglobin levels,... participants or investigators may be able to guesstimate if the participants are receiving the investigational drug based on these unique side effects (adverse events). 

Functional unblinding is an especially important issue in psychedelic drug (such as Lykos' therapeutics's MDNA) clinical trials. In FDA's guidance for industry (June 2023) "Psychedelic Drugs: Considerations for Clinical Investigations", 'functional unblinding' was discussed as the following. It raised the functional unblinding issue and provided some solutions for preventing/handling the functional unblinding: 

Functional unblinding is a critical concern in clinical trials where the investigational drugs have unique and distinctive side effects. Functional unblinding can introduce bias (consciously or unconsciously), affect participant behavior, influence how outcomes are measured and interpreted, and compromise the objectivity of the study's outcome.

If functional unblinding is suspected, it is difficult for sponsors to demonstrate that the functional unblinding does not occur. One approach to investigate/assess the functional unblinding is to employ questionnaires before the study unblinding to ask the participants and investigators which treatment group they think the participants are receiving. However, I see no or very few sponsors doing this. I described this in an earlier post "Assessing potential unblinding due to imbalance in side effects through exit questionnaires".