Non-smokers show acute tolerance to subcutaneous nicotine.

Plasma nicotine concentrations following subcutaneous (SC) injection were measured in six subjects who included three life-long nonsmokers. On average, a peak plasma level of 8.5 ng/ml (SD = 3.1) was reached 15 min after the mean dose of 13.25 micrograms/kg nicotine base. Subjective effects were reported by five subjects. The peak heart rate response (mean boost 11 beats per min at 10 min) preceded and was already declining by the time plasma nicotine concentrations peaked. Hysteresis plots showed clear evidence of acute nicotine tolerance in subjects who had never smoked, indicating that acute tolerance is not an acquired phenomenon. The acquisition by smokers of chronic tolerance to nicotine has not yet been systematically demonstrated. Reliable dose-response studies in smokers and nonsmokers are needed, and use of the SC route for this purpose is discussed.