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Su Keles
| Posted on October 11, 2022

Small molecules vs. Biologics: Understanding the differences


We’re used to changes. Technology is constantly evolving and surprising us with new ways of making our lives easier. We don’t go renting movies in the nearest Blockbuster anymore; platforms such as Netflix have enabled us to access thousands of movies at our fingertips. We don’t use the same tech tools we used a few years ago; we don’t do door-to-door marketing; we use online platforms to reach the maximum number of the audience. Similarly to other industries, the pharmaceutical industry has been experiencing its own technological revolution as more and more new biological drugs don’t cease to emerge into the market. One of these revolutions is the rising popularity of biologics, a more complex form of developing medicine. 

In order to have a better understanding of the differences between small and large molecules, It is essential to understand them individually at first. To avoid further confusion, large molecule drugs are also called biologics; both terms are perfectly acceptable. 

Actually, It’s likely that you have never used a large-molecule drug before. Small-molecule drugs are much more common. To put it in numbers, 90% of the top prescribed medications on the market are small-molecule drugs! So yes, you can be grateful to small molecule drugs like aspirin or paracetamol when that horrible headache strikes again. On the other hand, we could say that biologics drugs are commonly used for more specific situations; their efficiency is at the highest when treating cancer and autoimmune diseases.


What is a small-molecule drug? 

The simplest definition of small molecule drugs is that they are compounds with low molecular weight. A single molecule of a small molecular drug usually has only between 20 to 100 atoms. This doesn’t say much unless you’re a chemist with industry knowledge. So let’s put it in more practical terms.

Small molecule drugs have several benefits for patients but also for healthcare workers. Their simple and stable nature makes the patient’s acceptance easier. Plus, their simple nature makes them more predictable, resulting in less complicated dosing protocols. Small molecules can be appropriately characterized and easily purified and analyzed with regular lab tests. This isn’t the case with Biologics, especially the ones with larger sizes. They have a more complex and diverse blend of molecules, making them harder to characterize.

On the other hand, from an inventor’s point of view, the simplicity of small-molecule drugs can potentially lead to generic competition, which can be damaging in terms of profit after patent life. But, their development is simpler and cheaper than biologics since it doesn’t involve complicated manufacturing and regulatory processes. 


What are Biologics (large-molecule drugs) ?

On the other hand, biological drugs or large-molecule drugs are manufactured from living organisms, such as humans, plants, and microorganisms. Biologics are getting increasingly popular. These are typically larger in size than small-molecule drugs, with a single molecule usually having between 200 to 50.000 atoms. Again, it does not make much sense without industry knowledge.

So if 90% of the medicine we encounter are small molecule drugs, what are biologics? For instance, Insulin, the first biologic drug, has been used to treat diabetes for nearly a century. Vaccines are also considered large-molecule drugs. They play a more significant role than small molecule drugs in treating diseases such as cancer or genetic disorders. Until now, this seems too perfect. So what’s the catch? 

Biologics are relatively larger and more complex than small-molecule medicine. Unlike small molecule drugs, which are commonly administered orally due to their stable nature, biologics do not share the same nature. So, injections or infusions are the preferred methods for the administration of large-molecule drugs, which can make the patient’s compliance more difficult. One significant disadvantage of biologics is that they are much more expensive to produce, so they are also much more costly for patients. Another challenge in the way of biologics is that some patients can develop immune responses to the drugs, which results in less effective treatments over time. 

Biosimilars vs. Generic medicines

Talking about biologics without mentioning biosimilars would be unfinished business. As we mentioned earlier, biological drugs are expensive. The high cost of biologics leads to new legislation trying to provide more treatment options, increasing access and lowering costs. The result is Biosimilars. As the name implies, a biosimilar is a biologic that is highly similar but does not need to be perfectly identical to the original biological drug. The FDA requires biosimilar products to be highly similar to the original reference product. Biosimilars can cost up to 25-50% less since they are not patented. 

Wait. Doesn’t that sound like generic medicines? Yes, these are similar concepts. They share the same goal which is to offer a more affordable treatment option for some patients. But, unlike generic medicines, biosimilars are not exact copies but have high similarities to the active ingredient of the biologic. The reason behind it is simple, they are often more complex and are made from living cells rather than chemicals, which makes their nature variable and unpredictable.

If you want to refresh your memory on generic medicine, check out our blog!



It’s one of these situations where one is not better than the other, but both need to coexist to treat different diseases. Small molecules will always remain easier to synthesize and produce in large quantities, which will be more suitable for treating chronic conditions where patients need affordable medicines for long periods of time. In contrast, biologics excel and play essential roles in treating more complex diseases such as cancer, autoimmune and inheritable diseases.

Thanks for reading!

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