Photobiomodulation may offer effective pain management

This article provides an overview of the scientific literature on laser photobiomodulation (PBM) for pain management. It defines PBM, summarizes laser effects on pain and reviews key recommendations for effective parameters. 

We studied scientific literature from the last 10 years to ensure current results in the PubMed database. 

Note: PubMed, maintained by the National Center for Biotechnology Information (NCBI) at the U.S. National Library of Medicine (NLM), part of the National Institutes of Health (NIH), ensures data integrity. 

What is PBM?

PBM, also known as low-level laser therapy (LLLT), involves the application of light (commonly in the red and infrared spectrum) to stimulate biological processes, enhance ATP production, reduce inflammation and oxidative stress, alleviate pain and promote tissue repair.^1,2 

Our PubMed search revealed 1,120 papers with the word “pain” in the title or abstract, making it the most targeted subject (out of 4,764 papers) for studies and publications on PBM. These results include studies on both lasers and LEDs. 

We focused on meta-analyses on pain because they aggregate results from multiple studies to provide more robust and precise conclusions. This approach enhances statistical power, estimates overall effect sizes, identifies trends and evaluates variability among study outcomes.³ In total, we identified 282 meta-analyses. This large number indicates the topic is well-researched, making the findings more likely to be accurate and applicable. 

The papers retrieved addressed various types of chronic pain, including myofascial pain, rheumatoid arthritis, neck pain, ankle sprain, knee osteoarthritis, low-back pain, plantar fasciitis, myofascial pain syndrome, frozen shoulder, Achilles tendinopathy and carpal tunnel syndrome. They also covered pain management in oral surgery, orthodontics, post-orthognathic surgery and apical periodontitis. 

The majority of these studies demonstrated beneficial results for laser therapy in treating pain, highlighting its efficacy across a wide range of conditions. Additionally, LLLT has also been shown to be effective in treating fibromyalgia, oral mucositis in cancer patients, burning mouth syndrome, temporomandibular joint disorders and tonsillectomy pain. This further suggests the use of laser photobiomodulation as an effective modality for pain relief in both clinical and postoperative settings. 

Red or infrared lasers?

First, the evidence for red and infrared wavelengths was examined. There were 946 publications for red and 1603 for infrared. This indicates both wavelengths are well-documented and therapeutically relevant. 

The scientific literature clearly shows red and infrared lasers have distinct penetration capabilities in biological tissues due to their different wavelengths. Red lasers, typically between 630-660 nm, are optimal for superficial treatments and effectively promote skin healing, repair wounds and reduce pain and inflammation.⁴ In contrast, infrared lasers, ranging from 780-880 nm, penetrate deeper into tissues and make them ideal for treating muscles, joints and nerve injuries.^5,6 Although infrared light is also absorbed by superficial tissues, it continues to penetrate into deeper layers, making longer wavelengths preferable for deeper lesions. Conversely, shorter wavelengths are advantageous for more superficial treatments as they are primarily absorbed by target tissues near the surface.⁷ The cited research suggests that combining these two wavelengths is reasonable for positive therapeutic outcomes. 

Optimal parameters for pain relief

A recent meta-analysis was studied to determine the most important parameters influencing laser PBM’s effect on pain.⁸ This large-scale study involved Chukuka Enwemeka, PhD, FACSM, from San Diego State University, a well-respected researcher in photobiomodulation with more than 70 research papers. The study applied contemporary biomedical informatics tools to determine optimal treatment parameters for pain relief. 

A total of 96 articles on using lasers to treat pain in humans were reviewed, yielding 232 effect sizes. Laser wavelengths ranged from 632.8 to 1,064 nm, and the number of treatment sessions varied from one to 30. The studies showed laser therapy had a positive impact on pain relief, whether compared with placebo (73 articles), controls (eight articles) or alternative treatments (15 articles). 

The parameters analyzed included treatment duration (minutes), energy per point and session (Joules), total energy (J), energy density (J/cm²), frequency of treatment (sessions/week), power (Watts), power density (W/cm²) and the number of treatments. The analysis found total energy had the greatest effect on pain relief, followed by energy density and duration.⁸ The most effective total energy range was 120 to 162 J, followed by 15.36 to 20.16 J, with five additional optimal ranges between 0.72 and 8.56 J. 

The authors further evaluated studies within the largest number of data points (120–162 J and 15.36–20.16 J). The median wavelength was 830 nm, the 120–162 J group had more studies using shorter wavelengths (e.g., 633 nm), while the 15.36–20.16 J group had studies with longer wavelengths (e.g., 904 nm). The group of studies between 0.72 and 8.56 J was not further analyzed due to fewer publications. 

Although all parameters are important, this analysis shows total energy is particularly relevant for laser phototherapy and must be carefully set to achieve a reasonable success rate.⁸ 

Practical application of these findings

To facilitate practical use, the time required to reach the indicated energy levels with devices of different power outputs (W) was calculated. Power in phototherapy is generally measured in milliwatts (mW), where one milliwatt is one thousandth of a watt. Calculating total energy in Joules involves using power output (W or mW) and exposure time. Here’s a simplified approach: 

• Determine the power output (P) in watts (W). 

• Identify the exposure time (t) in seconds (s). 

• Calculate total energy (E) using the formula: E = P × t. 

• For example, if a device has a power output of 0.5 W (500 mW) and is applied for 200 seconds, the total energy delivered would be 0.5 W × 200 s = 100 J. 

Device Power Output	Energy Level (J)	Exposure Time (minutes)
10 mW	120 J	200 minutes
	162 J	270 minutes
100 mW	120 J	20 minutes
	162 J	27 minutes
1000 mW	120 J	2 minutes
	162 J	2.7 minutes

 

Conclusions from device comparison

Comparing 10 mW, 100 mW and 1000 mW devices for laser photobiomodulation suggests higher-power devices significantly reduce treatment time and improve patient and practitioner convenience by shortening sessions, allowing more patients to be treated efficiently. While lower-power devices may be suitable for treatments needing low energy or for sensitive patients, higher-power devices could be more effective for achieving therapeutic goals. Clinics should choose devices based on their specific treatment protocols and consider the versatility and efficiency of higher-power devices. Overall, delivering optimal total energy swiftly is crucial for effective pain relief, making higher-power devices more beneficial. 

Final thoughts

In summary, the research cited suggests red lasers are optimal for more superficial treatments due to their wavelength and penetration. Infrared lasers penetrate more deeply into tissues, making them ideal for treating muscles and joints. Combining red and infrared laser photobiomodulation is advisable for optimum therapeutic outcomes. 

An extensive meta-analysis by a renowned research group found total energy is the most critical parameter for the efficacy of laser treatment for pain. The research suggests the optimal range for positive outcomes is 120–162 J, with 15.36–20.16 J being the second-best range. These findings indicate higher-power laser devices (1000 mW) could offer significant advantages in terms of efficiency and effectiveness. 

FRANCISCO CIDRAL, ND, MSC, PHD, POSTDOC, is the founder and CEO of Scientifica Consulting. He holds a master’s degree and PhD in neurosciences and a postdoctorate in health sciences. Cidral is a professor of integrative medicine and neurophysiology, with a specialization in laser acupuncture and photobiomodulation. He has authored more than 35 scientific publications and books. Cidral is a board member of various scientific journals and international research groups. He can be contacted at cidral@scientificaconsulting.com. 

References 

1. Chamkouri H, et al. Brain photobiomodulation therapy on neurological and psychological diseases. J Biophotonics. 2023;17(1): e202300145. PubMed. https://pubmed.ncbi.nlm.nih.gov/37403428/. Accessed May 24, 2024. 
2. Kim SY, et al. Photobiomodulation therapy activates YAP and triggers proliferation and dedifferentiation of Müller glia in mammalian retina. BMB Rep. 2023;56(9):502-507. PubMed. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10547971/. Accessed May 24, 2024. 
3. Johnson MI, et al. Efficacy and safety of transcutaneous electrical nerve stimulation (TENS) for acute and chronic pain in adults: A systematic review and meta-analysis of 381 studies (the meta-TENS study). BMJ open. 2022;12(2):e051073. https://doi.org/10.1136/bmjopen-2021-051073. Accessed May 29, 2024. 
4. Aziz-Jalali MH, et al. Comparison of Red and Infrared Low-level Laser Therapy in the Treatment of Acne Vulgaris. Indian J Dermatol. 2012;57(2):128-130. PubMed. https://pubmed.ncbi.nlm.nih.gov/22615511/. Accessed May 24, 2024. 
5. Ribeiro BG, et al. Red and Infrared Low-Level Laser Therapy Prior to Injury with or without Administration after Injury Modulate Oxidative Stress during the Muscle Repair Process. PLoS One. 2016;11(4):e0153618. PubMed. https://pubmed.ncbi.nlm.nih.gov/27082964/. Accessed May 24, 2024. 
6. Salehpour F, et al. Therapeutic effects of 10-HzPulsed wave lasers in rat depression model: A comparison between near-infrared and red wavelengths. Lasers Surg Med. 201648(7):695-705. PubMed. https://pubmed.ncbi.nlm.nih.gov/27367569/. Accessed May 24, 2024. 
7. Enwemeka CS. Intricacies of dose in laser phototherapy for tissue repair and pain relief. Photomed Laser Surg. 2009;27(3):387-393. PubMed. https://pubmed.ncbi.nlm.nih.gov/19473073/. Accessed May 24, 2024. 
8. Kate RJ, et al. Optimal Laser Phototherapy Parameters for Pain Relief. Photomed Laser Surg. 2018;36(7):354-362. PubMed. https://pubmed.ncbi.nlm.nih.gov/29583080/. Accessed May 24, 2024.