  Objectives: Stress hormones have been associated with temporal discounting.
Although time-discount rate is shown to be stable over a long term, no study to
date examines whether individual differences in stress hormones could predict
individuals' time-discount rates in the relatively distant future (e.g., six
month later), which is of interest in neuroeconomics of stress-addiction
association.
  Methods: We assessed 87 participants' salivary stress hormone (cortisol,
cortisone, and alpha-amylase) levels and hyperbolic discounting of delayed
rewards consisting of three magnitudes, at the time-interval of six months. For
salivary steroid assays, we employed a liquid chromatography/ mass spectroscopy
(LC/MS) method. The correlations between the stress hormone levels and
time-discount rates were examined.
  Results: We observed that salivary alpha-amylase (sAA) levels were negatively
associated with time-discount rates in never-smokers. Notably, salivary levels
of stress steroids (i.e., cortisol and cortisone) negatively and positively
related to time-discount rates in men and women, respectively, in
never-smokers. Ever-smokers' discount rates were not predicted from these
stress hormone levels.
  Conclusions: Individual differences in stress hormone levels predict
impulsivity in temporal discounting in the future. There are sex differences in
the effect of stress steroids on temporal discounting; while there was no sex
defference in the relationship between sAA and temporal discounting.
