Concentrated oil distilled from rosemary leaves, applied to the scalp or inhaled. Best-supported: more scalp hair over six months of daily use, a short-lived lift in alertness, less anxiety before stressful procedures. Evidence is thin — mostly single small trials. Harms are modest: lasting skin allergy, scalp itching, brief blood-pressure rise. Products vary widely in composition. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Scalp hair density by fixed-position photograph or magnified count | No universal target; ≥10% gain from own baseline by month 6 | The only objective read on whether the protocol works |
| Forearm patch-test response at 48 hours | No redness, raised bumps or itch at the intended dilution | Detects allergy before whole-scalp exposure |
| Scalp redness and itch score (0–10 self-rating) | 0–1, and no increase over personal baseline | Distinguishes tolerable irritation from developing allergy |
| Resting blood pressure | 110/70 to 125/80 mmHg | Inhalation transiently raises both readings |
| Resting heart rate | 50–70 bpm | Tracks the sympathetic arousal produced by inhalation |
| Daytime sleepiness rating (Karolinska Sleepiness Scale) | 1–4 during working hours | Quantifies the claimed alertness benefit |
| Sleep quality (Pittsburgh Sleep Quality Index) | Global score ≤5 | Detects whether daytime use is costing night-time sleep |
Cadence: Patch test read at 48 and 96 hours; scalp tolerance weekly for the first month; blood pressure at four weeks if inhalation is daily; sleep-quality score monthly; scalp photograph at three and six months, then every six months for as long as the protocol continues.