The safety profile of photobiomodulation for knee pain is one of the most consistent findings across the entire research base. Across every level of evidence, from umbrella reviews and systematic reviews down to individual randomized controlled trials, no serious adverse events have been attributed to the therapy at the wavelengths and doses used for knee conditions. For a treatment that ranked #1 among all physical modalities for knee pain in a 2025 network meta-analysis, the safety record runs as strong as the efficacy data.
Key Takeaways
- No serious adverse events attributed to photobiomodulation across all knee-specific clinical trials, including the largest RCT (168 patients with 6-month follow-up), post-surgical trials, and trials in military populations.
- A 2025 umbrella review synthesizing 204 RCTs across all health conditions found no evidence of harm at any evidence level. A 2026 systematic review of 14 chronic pain RCTs found 13 of 14 studies reported zero adverse events.
- The contrast with standard knee pain treatments is the practical point: photobiomodulation carries none of the gastrointestinal, cardiovascular, renal, or immunosuppressive risks associated with NSAIDs, corticosteroids, or opioid analgesics.
Evidence from Umbrella Reviews and Systematic Reviews
The strongest tier of safety evidence comes from the reviews that pool everything below them. The 2025 umbrella review by Son et al. synthesized 15 meta-analyses and 204 RCTs across all health conditions and found no evidence of harm from photobiomodulation, with no safety signals across musculoskeletal, neurological, and inflammatory conditions at any evidence level.
Narrowing to the knee, Oliveira et al. (2024), published in Physical Therapy, pooled 10 knee OA RCTs and 542 participants and confirmed the therapy's tolerability, with no serious adverse events across the included trials. A 2026 systematic review by Ferreira et al. widened the lens back out to chronic pain across 14 RCTs and found the same pattern: 13 of the 14 studies reported zero adverse events, and the single study that logged any described them as transient and self-resolving.
The dose question is worth isolating, because it behaves differently for safety than for efficacy. The 2019 BMJ Open meta-analysis by Stausholm et al., covering 22 placebo-controlled knee OA trials, reported no safety concerns and noted that the dose-dependence of efficacy does not carry over to toxicity. Inadequate doses produce weaker clinical results without producing fewer adverse events, because adverse events are essentially absent across every dose range studied.
Evidence from Individual Knee-Specific RCTs
The individual trials tell the same story from closer range. The largest knee-specific RCT, Alqualo-Costa et al. (2021), ran 168 patients through a four-arm, double-blind design and reported no treatment-related adverse events in any group across the full 6-month follow-up. The Stausholm et al. (2022) trial combined laser therapy with strength training in 50 patients over 8 weeks with a 12-month follow-up, and again, nothing attributable to the laser.
The same finding holds in populations where you might expect it to break. Gavish et al. (2021) treated combat soldiers with anterior knee pain, a physically demanding group, and reported no treatment-related adverse events. So did the Bahrami et al. (2023) post-TKA trial, the Dos Santos Maciel et al. (2025) trial, the Pinto et al. (2022) individualized dosimetry trial, the Guidini Lima et al. (2022) strength-training augmentation trial, and the Pasin et al. (2025) four-arm comparison.
What makes the record persuasive is its uniformity across conditions that usually produce variation. Different wavelengths (660–940nm), different devices (LED and laser), different durations (single sessions through 12 weeks), different populations (elderly OA patients, combat soldiers, post-surgical patients), different countries, and the adverse-event column stays empty in all of them. For the full efficacy picture behind these same trials, see PBM for Knee Pain: Clinical Evidence.
Comparison to Standard Knee Pain Treatments
This comparison matters because most people weighing photobiomodulation are already taking, or have already tried, the alternatives.
NSAIDs (ibuprofen, naproxen, diclofenac) are the most commonly used medications for knee OA, and long-term use carries documented risks: gastrointestinal bleeding, cardiovascular events, kidney damage, elevated blood pressure. Guidelines recommend limiting sustained use, which leaves chronic-pain patients in a bind precisely when they need durable relief.
Corticosteroid injections come with their own ceiling, usually three to four per year, because of what repetition does to the joint. A 2017 JAMA trial found that repeated triamcinolone injections over two years produced significantly greater cartilage volume loss than saline. The treatment intended to manage the disease measurably advanced it.
Opioid analgesics carry well-documented risks of dependence, tolerance, cognitive impairment, falls in older adults, and respiratory depression. Here the Stausholm 2022 finding does double duty: patients in the laser group significantly reduced their analgesic and NSAID use at 12 months while keeping pain controlled. A therapy that lowers medication reliance addresses the safety problem from the medication side, not just its own.
Photobiomodulation works through the body's own cellular repair and anti-inflammatory machinery rather than introducing a compound. It has no known drug interactions, needs no metabolic clearance through the liver or kidneys, and produces no sedation, weight gain, cognitive impairment, or withdrawal. For older adults who cannot stay on long-term NSAIDs because of gastrointestinal or cardiovascular risk, it offers a tolerable route through entirely different biology.
Contraindications, Precautions, and Limitations
No serious adverse events appear in the knee pain literature, but standard precautions still apply. Direct application over active malignancies is contraindicated, given the therapy's cell-proliferative effects. Treatment should be kept off the pregnant uterus. Photosensitizing medications can alter how tissue responds to light, though no adverse interactions have surfaced in the knee OA trials. Patients with epilepsy should choose devices without strobing or flashing modes. LED-based home devices run at irradiance levels that remove the eye-safety risk of clinical lasers, but direct, sustained eye exposure is still worth avoiding.
Limitations of the Safety Evidence
The safety record is consistent, and it should be read with its limits in view. Most knee-specific trials enrolled tens to low hundreds of patients, sample sizes powered to detect efficacy, not rare events. A trial of 50 or 168 patients can show reliably whether a therapy reduces pain; it cannot rule out an adverse event that strikes 1 in 1,000 users. So the precise claim is that no serious adverse events have been reported across these trials, which is not the same as proof that none can occur.
Follow-up duration is the other bound. The longest knee-specific follow-up here is 12 months, and most trials ran for weeks, so multi-year safety data for sustained daily home use does not yet exist, and adverse-event monitoring quality varies from study to study. None of this cuts against the favorable signal; it frames it. Photobiomodulation has a strong short-to-medium-term safety record in controlled trials, with long-term and rare-event safety still to be characterized at scale.
Conclusion
For most people managing knee pain, the safety profile of photobiomodulation sits well above those of the NSAIDs, corticosteroid injections, and opioids that make up the standard pharmaceutical approach. Within the limits above, the picture is consistent: across hundreds of patients in controlled trials, across multiple wavelengths, device types, and treatment durations, no serious adverse events have been attributed to the therapy. That consistency is what supports sustained, daily home use without the cumulative-toxicity ceiling that constrains every pharmaceutical option currently available for chronic knee pain.
The safety data for photobiomodulation is remarkably clean. I've gone through the knee OA literature looking for the catch: Alqualo-Costa at 168 patients, Stausholm at 50, the Pasin comparison, post-surgical patients, combat soldiers. Zero serious adverse events across the board. Set that against the gastrointestinal and cardiovascular profile of long-term NSAIDs, or the cartilage-thinning concern with repeated cortisone, and the contrast is hard to ignore. For a patient who has to treat a chronic condition over years rather than weeks, that differential is most of the decision.— Dr. William Carter, MD
