Raman Spectroscopy—A Game-Changer in the Fight Against Counterfeit Drugs

The rise of counterfeit pharmaceuticals presents a significant global health threat, with fake medications potentially containing incorrect dosages, harmful substances, or the wrong ingredients. The World Health Organization (WHO) estimates that approximately 10% of medicines worldwide are counterfeit, with even higher rates in developing countries (1). Traditional detection methods, like high-performance liquid chromatography (HPLC) and mass spectrometry, while effective, are complex, time-consuming, and require expensive equipment. In contrast, Raman spectroscopy provides a rapid, non-destructive, and cost-effective alternative for identifying counterfeit drugs (2) (Table I).

What are the principles of Raman spectroscopy?

Raman spectroscopy is based on the inelastic scattering of monochromatic light, typically from a laser, as it interacts with molecular vibrations within a sample. When light photons collide with molecules, most are elastically scattered (Rayleigh scattering), but a small fraction undergoes inelastic scattering (Raman scattering), resulting in a shift in energy corresponding to the vibrational modes of the molecules. This shift provides a molecular fingerprint unique to the substance, allowing for its identification. Raman spectroscopy is particularly advantageous in pharmaceutical analysis because it is insensitive to water, requires minimal sample preparation, and can analyze samples through transparent packaging (3).

How is Raman spectroscopy used in detecting counterfeit drugs?

Raman spectroscopy has proven effective in detecting counterfeit pharmaceuticals. Combined with chemometric techniques like principal component analysis (PCA), it enables the identification of counterfeit medicines and differentiation of mixtures (4). It has also been used to detect non-steroidalanti-inflammatory drugs (NSAID) (5) residues in latent fingermarks, demonstrating its sensitivity and specificity (6). During the COVID-19 pandemic, the rise in counterfeit drugs underscored Raman spectroscopy’s value in rapid, non-destructive pharmaceutical screening (7). Additionally, Particle Correlated Raman Spectroscopy (PCRS) integrates Raman microspectroscopy with automated particle imaging and identification, enhancing forensic analysis by providing both physical and chemical insights into counterfeit drug samples (8).

What are some advantages of Raman spectroscopy?

Raman spectroscopy offers the following advantages in the detection of counterfeit drugs:

• Non-destructive analysis. Samples remain intact, preserving evidence for further investigation.
• Minimal sample preparation. Reduces analysis time and complexity.
• Rapid results. Provides immediate identification, facilitating on-site testing.
• Portability. Handheld Raman devices enable field analysis, allowing for the detection of counterfeit drugs at points of sale or distribution (9).
• Ability to analyze through packaging. Can assess pharmaceuticals without the need to open packaging, maintaining product integrity.

What are the limitations and challenges?

Despite its advantages, Raman spectroscopy has the following limitations (Table II):

• Fluorescence interference. Some substances may exhibit fluorescence under laser excitation, which can obscure Raman signals (10).
• Limited sensitivity for low-concentration components. Detecting trace amounts of a substance may be challenging without signal enhancement techniques.
• Requirement for reference libraries. Accurate identification relies on comprehensive spectral libraries for comparison (10).

Case study and real-world applications

Dr. Sayo Fakayode, a Professor of Chemistry at Georgia College and State University, has utilized Raman spectroscopy to detect counterfeit over-the-counter (OTC) medications (11). His research focuses on developing rapid detection methods for fake and toxic consumables that fall outside the regulatory reach of agencies, such as FDA. By combining Raman spectroscopy with chemometric techniques, such as regression analysis and PCA, Fakayode's team has achieved a 94% accuracy rate in predicting medication content, effectively distinguishing between authentic and counterfeit OTC drugs (12).

FDA's Forensic Chemistry Center employs Raman spectroscopy for counterfeit and unknown particle analysis (13). Chemists like Mark Witkowski use the technique to derive formulation information on counterfeit products, comparing them to authentic counterparts to identify discrepancies (6). The non-destructive nature of Raman spectroscopy preserves evidence, and its ability to analyze small particles makes it invaluable in forensic investigations.

A study demonstrating Raman’s effectiveness in characterizing drug formulations: polymorph characterization of active molecules using Raman microscopy.

Polymorph characterization of active molecules is crucial in the pharmaceutical industry, both in raw powders and final formulations. Raman microscopy provides an effective solution for analyzing polymorphic phases (14). This study presents an example of polymorph characterization using a Raman microscope equipped with a super low-frequency module. The results demonstrate the ability to distinguish between different polymorphic forms of carbamazepine, both in pure powder and tablet formulations.

The physical state of drug substances significantly affects pharmaceutical behavior, making it essential to understand crystallization, solid-state reactions, phase stability, and solubility (15). Various methods, including X-ray diffraction, optical microscopy, thermal analysis, and infrared spectroscopy, have been used to assess the solid-state composition of pharmaceuticals. Raman spectroscopy has emerged as a powerful tool for characterizing polymorphs, offering high spatial resolution, non-destructive analysis, and the ability to analyze microscopic samples without extensive sample preparation (16). This study investigates different polymorphic phases of carbamazepine, first as a pure powder and then in tablet form.

Methods. A Raman microscope (HORIBA LabRAM Soleil) was used for all analyses. This high-throughput instrument features a Raman optical design based on dielectric mirrors and high-quality gratings, minimizing signal loss and maximizing spectral resolution. Because polymorphic phases differ in crystal modes, their characterization requires analysis in the low Raman frequency region. The microscope’s super low frequency module enables measurements as low as 30 cm⁻¹ without additional modifications, ensuring high Raman throughput.

Results.In the first phase of the study, single spectra of raw carbamazepine powder were analyzed. Two distinct spectral signatures were observed, differing mainly in the low-frequency region below 50 cm⁻¹. Specifically, a characteristic band at 40 cm⁻¹ was identified for Form I, allowing clear discrimination between polymorphic phases.

Raman microscopy was also used to analyze a homemade tablet containing different forms of carbamazepine mixed with excipients. A Raman map was generated to locate carbamazepine particles and determine their polymorphic phases. Using spectral data from 30–50 cm⁻¹, Forms I and III were successfully distinguished within the tablet matrix. The results highlight the capability of Raman microscopy to map polymorphic distributions in formulated products.

Data. Raman microscopy was also used to analyze a homemade tablet containing different forms of carbamazepine mixed with excipients. A Raman map was generated to locate carbamazepine particles and determine their polymorphic phases. Using spectral data from 30–50 cm⁻¹, Forms I and III were successfully distinguished within the tablet matrix. The results highlight the capability of Raman microscopy to map polymorphic distributions in formulated products.

Conclusion. Raman microscopy is a valuable tool for characterizing polymorphic phases of APIs. A super low-frequency capability provides a reliable method for detecting crystal phase bands with no compromise on acquisition time. This capability is essential for accurate pharmaceutical characterization and quality control, making it a crucial technique in drug development and manufacturing.

Future perspectives and challenges

Despite its growing applications, Raman spectroscopy faces challenges such as fluorescence interference and the need for more extensive spectral libraries. The integration of artificial intelligence (AI) and machine learning could address these issues, enabling real-time spectral analysis for faster, more accurate results in complex mixtures. Additionally, expanding Raman technology to resource-limited settings remains a key objective. Collaborative efforts between governments, non-governmental organizations (NGOs) and the private sector could facilitate the deployment of portable Raman devices worldwide, particularly in regions where counterfeit drugs pose significant health risks. Overcoming these challenges will further solidify Raman spectroscopy’s role in pharmaceutical analysis, ensuring safer and more reliable drug supplies globally.

Governments and regulatory bodies must prioritize the widespread adoption of advanced detection methods like Raman spectroscopy. By investing in technology and training, they can build robust infrastructures for monitoring pharmaceutical authenticity. Public awareness campaigns, highlighting the dangers of counterfeit drugs and the technologies used to combat them, could further empower consumers and healthcare professionals to recognize and report suspicious medications.

As Raman spectroscopy becomes more sophisticated, it promises a future where counterfeit pharmaceuticals are not merely identified but preemptively eliminated from the supply chain. By ensuring the integrity of medicines, this technology stands as a critical ally in safeguarding global health. Its role extends beyond detection—it serves as a testament to the power of innovation in addressing one of the most pressing challenges of modern healthcare.

References

1. WHO. General Information on Counterfeit Medicines. WHO.int. https://www.who.int

2. Lohumi, S.; Lee, H.; Lee, S.; Cho, B.K. A Review of Application of Raman Spectroscopy in Agriculture and Food Science. Trends Food Sci Technol. 2015;46(1):85–98.

3. O’Brien, N. A.; Cain, K.; Kibbey, C.; Sy, S. K. B.; Khan, M. A. Applications of Raman Spectroscopy in Pharmaceutical Drug Development: A Review. Mol. Pharmaceutics 2021, 18 (8), 3076–3092. DOI: 10.1021/acs.molpharmaceut.1c00278

4. Marques, M. B.; Pereira, C. F.; Sena, M. M. Detection and Classification of Counterfeit Medicines Using Raman Spectroscopy and Chemometric Techniques. Talanta 2022, 242, 123197. DOI: 10.1016/j.talanta.2022.123197

5. Non-Steroidal Anti-Inflammatory Drugs (NSAID). (Expansion of acronym)

6. Witkowski, M.M.; et al. Enhancing Pharmaceutical Forensics with Raman Spectroscopy: Applications and Advances. Pharm Anal Chem J. 2019;8(3):101–15.

7. NIH. Advancements in Raman Spectroscopy: Detecting Pharmaceutical Fraud. https://www.nih.gov

8. Deidda, R.; Sacre, P. Y.; Clavaud, M.; Avohou, H. T.; Hubert, P.; Ziemons, E. Raman Spectroscopy in Pharmaceutical Quality Control: Critical Review of Modern Techniques. J. Pharm. Biomed. Anal. 2019, 147, 557–573. DOI: 10.1016/j.jpba.2017.03.044

9. Smith, R.; Wright, K.L.;, Ashton L. Raman Spectroscopy: Applications in Pharmaceuticals and Beyond. Analyst. 2016;141(13):3590–600.

10. Eberhardt, K.; Stiebing, C.; Matthäus, C.; Schmitt, M.; Popp, J. Advantages and Limitations of Raman Spectroscopy for Molecular Diagnostics: An update. Expert Rev Mol Diagn. 2015;15(6):773–87.

11. Fakayode, S.O.; Donald, W.W. Detection of Counterfeit Over-the-Counter Medications Using Raman Spectroscopy and Chemometric Analysis. Am J Anal Chem. 2020;11(7):442–51.

12. Fakayode, S. O.; Ritchie, H. L.; Yakubu, M.; Pollard, D. A.; Lawal, O. M. Non-Destructive Spectroscopic Techniques for Identifying Counterfeit Over-the-Counter (OTC) Medications: A Case Study. Forensic Chem. 2021, 22, 100306. DOI: 10.1016/j.forc.2021.100306

13. FDA. Forensic Chemistry Center. FDA’s Role in Detecting Counterfeit Pharmaceuticals. FDA. https://www.fda.gov.

14. Atkins, C.G.; Buckley, K.; Blades, M.W.; Turner, R.F.B. Raman Spectroscopy of Biological Samples and Tissues: Shining a Light on the Future of Clinical Diagnostics. Spectroscopy. 2017;32(1):14–21.

15. Witkowski, M. R.; Oliver, N. S.; Bell, S. E. J. The Role of Raman Spectroscopy in Detecting Counterfeit Pharmaceuticals. Analyst 2020, 145 (15), 4991–5003. DOI: 10.1039/D0AN00954A

16. Matousek, P.; Parker, A.W. Non-Invasive Detection of Counterfeit Drugs by Spatially Offset Raman Spectroscopy. Anal Chem. 2006;78(7):2299–305.

About the author

Dr. Michelle Sestak joined HORIBA in 2012 after earning a Ph.D. in physics from the University of Toledo. She specialized in spectroscopic ellipsometry for cadmium telluride thin-film solar cells. Starting as a thin film applications scientist, she later expanded into Raman spectroscopy and now works as a Raman and thin films applications scientist.