The effects of five stimulants, which are commonly used by long distance truck drivers, were evaluated to compare their ability to reduce fatigue. The stimulants were caffeine (200 mg), ephedrine hydrochloride (60 mg), pseudoephedrine hydrochloride (60 mg), phentermine (30 md) and diethylpropion hydrochloride (75 mg). No significant differences in performance were found among the five drug treatments on the 4th hour of a 3-way divided attention task or during a post-testing session (2-way divided attention, digit symbol coding, critical flicker fusion frequency). Systolic blood pressure and oral temperature were not differentially affected by the drugs but a significant treatment difference was found for diastolic blood pressure. Psuedoephedrine caused the greatest increase in diastolic blood pressure, when compared with diethylpropion and phentermine. Ephedrine produced the second largest increase, which significantly exceeded that after diethylpropion. Heart rate (HR) was found to be significantly lower after caffeine than after ephedrine, pseudoephedrine, phentermine or diethylpropion. Heart rate variability (sd of HR) was found to be significantly greater after ephedrine than after phentermine or diethylpropion. Caffeine was significantly less likely than ephedrine, pseudoephedrine, phentermine or diethylpropion to cause a reduction in the spectral power of the blood pressure component of the cardiac frequency signal. These results suggest that none of the five stimulants, when taken in normal therapeutic doses, differ greatly in their capacity to improve performance and that differences among the drugs are mainly related to their effects on the cardiovascular system. (A)
Abstract