BackgroundVitamin D delivered transdermally may suppress hyperactivity in nociceptor pain receptors and alter pain intensity, offering a useful addition to localised pain management in varying clinical settings. Currently, little is known about long-term usage of continuous-release vitamin D patches.MethodWe conducted a randomised parallel pilot trial to evaluate safety and tolerability of daily application of patented (US8821921B2) transdermal vitamin D patches over 8 weeks and assess time-level profile of serum vitamin D. Compliance, tolerance and sun exposure were monitored daily, serum 25(OH)D measured 2-weekly and dietary intake and safety markers 4-weekly.ResultsThirty healthy adults were randomised to two treatment groups: big patch and small patch. mean age was 36 years (20–68 years) with a 63% female to 37% male split. Patches differed in size but contained identical ingredients including 30 000 IU cholecalciferol. Physical and blood safety markers remained stable, within normal clinical parameters, and with no clinically meaningful changes throughout. Five big patch participants experienced skin irritation, which was mild and occasional for three, but continuous for two leading to patch withdrawal. There were no skin reactions in small patch group. average, serum 25(OH)D levels increased by +14 nmol/L (SD 11.63, range, −4 to 40 nmol/L) between baseline and week 8, with no significant differences between patch sizes. There was a shift in overall vitamin D status between baseline and week 8 (23% deficient (<30 nmol/L) decreasing to 0%, and normal (>50 nmol/L) increasing from 37% to 70% at week 8).ConclusionBased on these results, long-term (8 weeks) application of patented transdermal vitamin D patches was found to be safe. There may be minor skin tolerance issues with big patches for some, which appears to relate to patch size. Larger trials are warranted to explore the increase in vitamin D levels beyond 8 weeks.Trial registration numberNCT04851990.