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The FDA review process can be one of the most intimidating parts of��developing and manufacturing a new medical device.��You’ve��invested time, money, and momentum into your product. You may even have strong early data or a working prototype. But then you hear stories of devices getting stuck, delayed, or outright rejected during FDA review, and suddenly the risk feels very real.��

At 91�Թ� Engineering, we often work with teams navigating product development and regulatory expectations. What we’ve noticed is that most FDA failures aren’t because the product is a bad idea; they happen because of avoidable gaps in planning, documentation, or alignment with FDA expectations. 

Top 10 Reasons Medical Devices Fail FDA Review

These are 10 of the most common reasons��medical devices��fail FDA review, along with practical insight on how to avoid them.��

1. Inadequate Clinical Evidence

One of the most common reasons devices fail FDA review is straightforward: there isn’t enough evidence to prove safety and effectiveness. For startups, this often happens when teams try to minimize time and cost by collecting “just enough” data. The problem is that what feels sufficient internally may not meet FDA expectations. 

This can show up in a few ways: 

• Clinical studies that are too small or poorly designed����
• Endpoints that��don’t��clearly support the intended use����
• Data that��doesn’t��match the claims being made����

How to avoid it:��
Start with a clear clinical strategy early. Align your study design with FDA guidance or get feedback through a��pre-submission��before running trials.��

2. Poorly Defined Intended Use or Indications for Use

If the FDA can’t clearly understand what your device is supposed to do, that’s a problem. This is especially common for startups trying to maximize market opportunities early. 

Common issues include: 

• Claims that are too broad or vague����
• Mismatch between labeling and actual data����
• Trying to position the device for multiple uses without proper support����

How to avoid it:��
Be specific and focused. Define your intended use tightly and make sure every piece of data supports that claim.��

3. Weak Design Controls and Documentation

Your Design History File (DHF) tells the story of how your product was developed. If that story has gaps, the FDA will notice. Even strong medical products can fail FDA review if the documentation doesn’t prove how they were built and tested. 

Common red flags are: 

• Missing design inputs or outputs����
• Poor traceability between requirements, risks, and testing����
• Incomplete verification or validation records����

How to avoid it:��
Treat documentation as part of development, not an afterthought. Build traceability from day one��using date stamps and revision history.��

4. Incomplete Risk Management (ISO 14971 Issues)

The FDA expects you to identify, assess, and mitigate risks in a structured way. For connected or complex devices, this is even more important (more explanation in the next section). 

Failures often include:��

• Missing hazard analyses����
• Incomplete risk controls����
• No clear risk-benefit justification����

How to avoid it:��
Follow����closely and ensure every identified risk is tied to a mitigation and validation activity.��

5. Software Validation and Cybersecurity Gaps

If your device includes��software��(and most do nowadays), this is a big one.��The FDA has increased its scrutiny here, especially for connected devices.��

Common problems: 

• Incomplete software verification and validation����
• Lack of documentation around software lifecycle processes����
• Missing cybersecurity controls or threat analysis����

How to avoid it:��
Document your software development process thoroughly and include cybersecurity considerations from the start.��

6. Biocompatibility and Material Safety Issues

Your device interacts with the human body, so the FDA needs to know it’s safe. Teams sometimes underestimate how much testing is required. 

Failures often stem from: 

• Missing biocompatibility testing����
• Using materials without proper justification����
• Relying on assumptions instead of evidence����

*Note: Research the potential future changes of medical device materials, as we may see the removal of materials that aren’t biodegradable or sustainable soon, and it may have an impact on approval.  

How to avoid it:��
Follow����guidance and plan testing early based on how and where the device is used.��

7. Manufacturing and Quality System Deficiencies

The FDA isn’t just evaluating your product. They’re evaluating your ability to consistently produce it. Startups and small businesses often delay building a formal quality management system, which can create problems later. 

Common issues include: 

• Lack of a compliant��quality management system��
• Incomplete��process validation����
• Poor supplier controls����

How to avoid it:��
Implement quality systems early, even if��you’re��not manufacturing at scale yet.��

8. Disorganized or Incomplete FDA Submissions

Even if everything else is solid, a messy submission can slow you down or lead to rejection. Remember, FDA reviewers are human. If your submission is hard to follow, that works against you. 

Common problems: 

• Missing required sections����
• Inconsistent information across documents����
• Lack of clarity in how data is presented����

How to avoid it:��
Structure your submission clearly and review it from the perspective of someone seeing it for the first time.��

9. Ignoring FDA Guidance or Feedback

The FDA provides guidance documents for a reason. Don’t ignore them! 

This includes: 

• Not following device-specific guidance����
• Skipping the Pre-Submission () process����
• Misinterpreting or overlooking FDA feedback����

How to avoid it:��
Engage early. Use the��Pre-Sub��process to��validate��your approach before investing heavily in testing.��

10. Lack of a Clear Regulatory Strategy

This is the underlying issue behind many of the failures listed here. 

Without a clear strategy, teams can easily: 

• Choose the wrong regulatory pathway (510(k), De Novo, PMA)����
• Underestimate data requirements����
• Build the product without aligning to regulatory expectations����

This often leads to rework, delays, and added costs. 

How to avoid it: 
Define your regulatory strategy early and revisit it as your product evolves. 

How Often Do Devices Fail FDA Review?

Most devices��aren’t��outright rejected, but many receive deficiency letters asking for more information. This can add months (or longer) to your timeline, increase development costs, and/or delay market entry and revenue.����

Can You Recover After a Failed FDA Review?

Absolutely. Treat their feedback as direction, not��a setback, and follow the tips in this article. Teams that recover��well:����

• Address every FDA comment thoroughly��
• Communicate clearly with reviewers��
• Bring in outside expertise when it’s needed��

Should You Bring in Outside Help?

For many startups and small engineering teams, the answer is yes. 

Regulatory and product development partners can help you avoid common mistakes, build stronger documentation and systems, and move faster with fewer surprises. While it will cost you money to hire an external resource, it often pays to have an outside perspective. 

Need Help Preparing for FDA Review?

If��you’re��building a medical device and want to reduce risk before submission, it can help to have an experienced team in your corner. At 91�Թ� Engineering, we work with engineering teams and startups to:��

• Strengthen design controls and documentation����
• Align product development with regulatory expectations����
• Identify��gaps before they become costly delays����

If��you’re��unsure whether your device is ready for FDA review, or you want a second set of eyes on your process,��we’re��here to help.��Start the conversation with our team online.��