Basics of Drug Development

In previous posts, we've explored both the biggest bottleneck in drug development and a potential way to expedite it.

It might be helpful to take a step back and ask a basic question: what exactly is drug development? 

Understanding the Different Parts of Drug Development

At a high level, drug (or biopharmaceutical) research and development is the entire process of discovering and testing a new drug. The goal of this process is to market and sell the new drug for patient use. 

As shown in the figure below, this process can be broadly divided into two periods:

  1. Drug discovery (in orange/yellow). The goal of discovery is to find a drug for a particular disease.
  2. Clinical development (in green/blue/purple). The goal of clinical development is to demonstrate that a new drug is safe and effective for people.

Since Unlearn focuses on applying machine learning to clinical development, we will solely discuss clinical development in this post. 

Bird's-Eye View of Clinical Development

Many people describe clinical development as challenging. So here's another question worth asking: why is clinical development so difficult? 

Here are some of the main reasons:

  1. It takes up to a decade to complete and is expensive: phase III clinical trials for Alzheimer's disease, for example, cost ~$40,000/subject [1]. If 2000 subjects are recruited [2], the cost would amount to $80 million. 
  2. High rates of failure occur at different steps of clinical development. Almost 70% of clinical trial sites fail to meet enrollment requirements for a given trial [3]. 90% of drugs that enter clinical trials don't make it to market [4]. 
  3. Multiple key stakeholders - with different roles and concerns - must all work together to bring a drug from clinical development to market.

The three major stakeholders include:

  • Biopharma companies (e.g. Pfizer), which develop the drug and finance the process from clinical development to post-marketing. Their primary concern is, "Will we be able to generate profits from the new drug and help the greatest number of patients?"
  • Human subjects [5], who participate in a key step of clinical development called clinical trials. Their primary concern is, "Will the treatment work for me?"
  • The Food and Drug Administration (FDA), the regulatory agency responsible for approving new drugs. They ask two important questions: "is the drug safe, and does it work in intended patients?"

Phases of Clinical Development

Now that we've talked about what clinical development is overall, including the main challenges and key players -you might be asking this question: what happens during the main steps of clinical development?

So let's dive right in.

In order to begin testing a new drug in people, the biopharma company must submit an investigational new drug application (IND) to the FDA. Once the IND is approved, the company can begin conducting clinical trials with human subjects. Clinical trials are necessary to make sure the drug is safe and works in people. As written in this post, the company must first identify and activate clinical trial sites, as well as recruit eligible subjects to participate.  

A typical clinical trial occurs in 4 phases, the order of which is prescribed by the FDA.

  • Phase I studies assess the safety of the new drug in 20-80 healthy volunteers over several months. The goals of this phase are to determine how the drug impacts the body (e.g. absorption, metabolism, and excretion) and what side effects occur as dosage increases. If participants are able to take the drug without serious side effects, the drug is deemed safe and passes Phase I. About 70% of drugs successfully complete Phase I. 
  • Phase II studies test whether the new drug works and further evaluate safety over several months to years. These studies recruit 100-300 patients with the condition the drug is meant to treat. If the drug is shown to be safe and effective, it passes Phase II. About 33% of drugs successfully complete Phase II.
  • Phase III studies recruit even more patients (1000-3000) and can last for several years. The purpose of phase III is to assess whether the new drug is better than or the same as existing drugs for the same condition. Phase III studies also confirm efficacy of the new drug and monitor rare and/or long-term side effects that may not have come up in the previous phases. If the new drug is at least as safe and effective as other drugs on the market, the new drug passes Phase III. About 70-90% of drugs that enter Phase III successfully complete this phase. 

Once Phase III is complete, the company can submit a new drug application (NDA) to the FDA. The FDA reviews the NDA to decide whether to approve the company's drug.

After the FDA approves the NDA, the company will conduct phase IV trials, or post-marketing monitoring and research. During this phase, the company can track the safety, benefits, and optimal use of the drug after it becomes available to patients. By collecting information during this phase, the FDA can make necessary changes to the drug (e.g. best dosage or whether it can be used with other drugs) [6]. 

That's basically it! This post should help you better understand what clinical development is and how it works generally [7]. In future posts, we will talk more about clinical trials - innovative trial designs, patient perspectives, and other relevant issues.






[5] Although human subjects and patients are often used interchangeably, they are not necessarily the same term according to the FDA. The FDA defines a human subject as "an individual who is or becomes a participant in research, either as a recipient of the test article or as a control. A subject may be either a healthy individual or a patient."

[6] Facts about each phase adapted from and

[7] For more details about clinical development, consult steps 3-5 on the FDA website:

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