Chronic autoimmune thyroiditis, commonly known as Hashimoto’s thyroiditis, is one of the conditions functional medicine practitioners see most often and treat with the most layered protocols: selenium repletion, vitamin D correction, sometimes dietary elimination, alongside conventional levothyroxine management by the patient’s physician. Photobiomodulation (PBM) directed at the thyroid gland has been added to some of these protocols for over a decade, and a genuine, if narrow, clinical trial literature exists on photobiomodulation for Hashimoto’s. This article looks specifically at what happens to the evidence when PBM is evaluated as an addition to an existing biochemical protocol rather than as a standalone intervention, because that is the decision most practitioners integrating laser into functional medicine practice are actually facing: not “does PBM treat Hashimoto’s” but “does adding PBM to what I am already doing change the outcome, and for how long.”
Two largely independent lines of clinical trial work exist. The first is a single Brazilian research group led by Höfling and colleagues, who published a pilot study (Höfling et al., 2010 pilot study), a randomized placebo-controlled trial, two mechanistic substudies, and a long-term follow-up between 2010 and 2018, all drawing on overlapping cohorts of patients with chronic autoimmune thyroiditis (CAT)-induced hypothyroidism. The second is a more recent Kosovo-based group (Berisha-Muharremi and colleagues) who, from 2023 onward, tested PBM explicitly as an add-on to a standing selenium and vitamin D protocol rather than against placebo alone. A third data point, from a Turkish group (Tunç and colleagues), used a properly sham-controlled design focused on oxidative stress and quality-of-life outcomes rather than thyroid hormone status. A 2026 systematic review by Berisha-Muharremi and Humolli pulls these together and is candid about how thin the field still is.
The core randomized, placebo-controlled trial (n=43, 830 nm continuous-wave diode laser, 50 mW output, cumulative fluence 707 J/cm2 delivered over 10 sessions across five weeks) found that patients receiving active PBM required a significantly lower levothyroxine dose at nine months than the placebo group (38.59±20.22 µg/day versus 106.88±22.90 µg/day, P<0.001), and that 47.8 percent of the laser group did not require levothyroxine at all during the follow-up period (Höfling et al., 2013 RCT). A companion substudy using color Doppler ultrasound reported changes in thyroid vascularization consistent with reduced local inflammatory activity in the treated group (Höfling et al., 2012 Doppler substudy), and a further substudy reported changes in serum TGF-β1 concentrations in the laser group, proposed as a plausible immunomodulatory mechanism — TGF-β signaling is associated with immune tolerance and downregulation of Th1-mediated autoimmune activity (Höfling et al., 2014 TGF-β1 substudy). This is a proposed mechanism, not a demonstrated one at the level of causal proof; the substudy shows an association, not a verified mechanistic pathway.
The finding that changes what a practitioner should actually say to a patient is the six-year follow-up of that same cohort (Höfling et al., 2018 long-term follow-up). At six years, the levothyroxine dose difference between groups had narrowed but remained statistically significant (94.50±44.45 µg/day in the laser group versus 141.72±52.62 µg/day in placebo, P=0.003), while the difference in anti-TPO antibody titers, which had been a notable finding earlier, was no longer statistically significant (P=0.166). The authors’ own description of this is direct: the therapeutic benefit observed at nine months had partially reversed by six years, and they conclude the effects of PBM in this application are transient rather than durable, implying that repeat courses or maintenance dosing would likely be needed to sustain any gain. This is an established finding from the same investigators who reported the original benefit, which arguably gives the reversal more weight than an independent negative replication would carry — the group had every incentive to report a durable result and reported the opposite. For a functional medicine practitioner discussing this with a patient, the honest framing is that PBM directed at the thyroid gland, on this specific protocol, behaves as a time-limited modifier of the trajectory of hypothyroidism, not a one-time correction. The reassuring counterpoint from the same follow-up: thyroid nodule formation did not differ meaningfully between groups (12 percent laser versus 16.7 percent placebo, all benign), which is a useful safety data point for a therapy applied directly over glandular tissue, though the sample is too small to rule out rare effects.
It is worth being explicit that all five of these Höfling-group publications draw on the same underlying trial infrastructure rather than being independent replications of each other. That matters for how much weight the body of work as a whole should carry — it is one well-conducted trial examined from several angles, not five separate confirmations.
The more directly relevant literature for functional medicine integration is the Kosovo-based work, because it was designed around the actual clinical question of adding PBM to a standing protocol rather than testing PBM in isolation. In the 2023 feasibility trial, both study arms received selenium 100 µg daily and vitamin D3 repletion where indicated, with one arm additionally receiving PBM (820 nm, 200 mW, 32 J/cm2 per point across eight points around the thyroid, twice weekly for three weeks) (Berisha-Muharremi et al., 2023 feasibility trial). At six months, the combined-therapy group showed significantly greater improvement across TSH, free T3, free T4, anti-TPO, anti-Tg, BMI, and required levothyroxine dose compared with the supplement-only group (P<0.05 across measures, several reaching P<0.0001). Two things temper how this should be read. First, attrition was substantial: 37 patients were enrolled per arm, but only 18 and 20 respectively completed six-month follow-up — close to half the original sample was lost, which is a meaningful threat to the validity of the reported effect sizes in either direction. Second, this was explicitly framed by the authors as a feasibility trial, meaning it was designed to establish that the combined protocol could be run and evaluated, not to provide a definitive efficacy estimate.
The same group’s 2025 study addressed sample size directly, enrolling 98 women and retaining 97 of them (51 combined-therapy, 46 supplement-only) over 12 months, and again found significantly greater improvement in the combined group across thyroid volume normalization, weight, BMI, waist-to-hip ratio, TSH, anti-TPO, anti-Tg, and levothyroxine dose requirement (Berisha-Muharremi et al., 2025 12-month trial). This is a considerably stronger dataset than the 2023 pilot in terms of retention and sample size, and it is the best current evidence specifically addressing the functional-medicine-relevant question of PBM as an add-on rather than a monotherapy. It is still a single research group’s output, has not yet been independently replicated by investigators outside that group, and — because both arms received supplementation and only one arm received PBM as well — the trial cannot separate whether the improvement over supplements alone reflects a direct thyroid effect of the laser, a systemic effect (note the BMI and waist-to-hip ratio changes, which are not thyroid-gland-specific outcomes), or some interaction between the two interventions. That co-intervention design is a real strength for external validity (it reflects how PBM is actually used in practice) and a real limitation for mechanistic interpretation (it cannot isolate PBM’s independent contribution).
The Turkish sham-controlled trial is useful precisely because it is the most rigorously blinded of the group and did not find what the others found. Forty-six patients were randomized to active or sham LLLT twice weekly for three weeks; the active group showed significantly greater improvement in oxidative stress biomarkers (including glutathione) and quality-of-life scores than the sham group, but the report does not describe significant short-term changes in thyroid hormone status attributable to active treatment over this three-week window (Tunç et al., 2024 sham-controlled RCT). Read alongside the other trials, this suggests two possibilities worth holding as genuinely open rather than resolved: that oxidative-stress and subjective quality-of-life improvements may be detectable on a shorter timeline than measurable endocrine change, or that the endocrine effects reported in the other trials depend on protocol or population features (dose, session count, co-administered supplements, baseline antibody titer) not present in this design. Either explanation is a hypothesis at this point, not an established finding.
The most recent systematic review on this topic, covering six eligible human clinical studies from Brazil, Turkey, and Kosovo published between 2010 and 2025, states plainly that the clinical evidence base is scarce and heterogeneous, and that randomized, sham-controlled trials with standardized protocols are needed before clinical implementation can be more strongly recommended (Berisha-Muharremi et al., 2026 systematic review). The review’s stated limitations map closely onto everything above: small samples across studies, wide variation in wavelength, power, and fluence between protocols, multiple studies confounding PBM with co-administered selenium and vitamin D so that the independent contribution of PBM cannot be determined, inconsistent sham control, and follow-up periods generally too short for a chronic autoimmune disease. This is the field’s own most current assessment of itself, and a practitioner integrating PBM into a Hashimoto’s protocol should read it as the baseline caveat against which any single positive trial result is weighed.
Several decision points follow directly from this evidence picture rather than from general principle. First, protocols are not interchangeable: the Höfling group’s parameters (830 nm, 50 mW, high cumulative fluence over 10 sessions) and the Berisha-Muharremi group’s parameters (820 nm, 200 mW, 32 J/cm2 per point across eight points, six sessions) are meaningfully different regimens tested in different trial designs; a musculoskeletal PBM protocol should not be assumed to transfer to thyroid application, and neither should either thyroid protocol be assumed superior without a head-to-head comparison that does not yet exist. Second, if PBM is being added to an existing selenium/vitamin D protocol, the current best evidence for that specific combined approach is the 2025 Kosovo trial, and it should be presented to patients and colleagues as promising but single-group, non-replicated evidence, not as an established standard. Third, if PBM is being applied as a standalone intervention, the durability data from the Höfling six-year follow-up should inform expectations: benefit measured at nine months is not necessarily benefit that persists at six years, and the antibody-suppression finding specifically did not hold up over time. Fourth, and non-negotiable: no trial in this literature supports adjusting levothyroxine dosing based on a PBM protocol independent of the prescribing physician’s serial TSH monitoring — dose changes remain a medical decision driven by biochemistry, not by session count. Finally, evidence specific to combining PBM with other common functional medicine interventions for Hashimoto’s — dietary gluten elimination, myo-inositol, or broader nutraceutical stacks beyond selenium and vitamin D — is currently absent from the published literature. If a practitioner is running PBM alongside those specific interventions, that particular combination has not been studied, and any outcome observed in that context is clinical observation, not trial-supported evidence.
The literature on PBM in Hashimoto’s thyroiditis is real, traceable, and larger than a single study, but it remains the output of only three research groups, and most of it from two of them, with the strongest sham-controlled data showing benefit on oxidative stress and quality of life rather than on thyroid hormone status, and the longest follow-up data showing that early endocrine gains are not fully sustained. The most clinically relevant recent work for functional medicine integration specifically tests PBM as an addition to standing selenium and vitamin D supplementation and finds a benefit over supplementation alone, but that finding still awaits independent replication outside the group that produced it. Treating this evidence as sufficient to promise durable remission or antibody normalization would overstate what six studies from three research groups, with the limitations described above, can support.
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