A preliminary investigation into the effect of coffee on hypolagesia associated with transcutaneous electrical nerve stimulation

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive, inexpensive analgesic technique used to relieve pain. It has been suggested that caffeine, an adenosine antagonist, may interfere with TENS action. This double-blind controlled pilot study investigated the effect of coffee on response to TENS in healthy human participants experiencing experimentally induced pain. Twelve participants (7 female, age range = 20-41 years) took part in two experiments separated by 24 h. Each experiment lasted 80 min and consisted of 3 x 15 min cycles: pre-TENS, during TENS predrink and during TENS postdrink [coffee (100 mg caffeine) or decaffeinated coffee randomized across experiments]. During each cycle, thresholds for electrical (EPT), mechanical (MPT) and cold pressor (CPT) pain were recorded. The statistical analysis modelled the responses for the coffee and decaffeinated coffee conditions during TENS (i.e. as a standard crossover) and detected no statistically significant effects between coffee and decaffeinated drinks for the natural logarithm (ln) transformed values of electrical pain threshold [ln EPT Coffee-ln EPT Decaffeinated coffee mean (standard error) = 0.0147 (0.2159)], mechanical pain threshold [ln MPT Coffee-ln MPT Decaffeinated coffee mean (standard error) = 0.1296 (0.0816)] and cold pain threshold [ln CPT Coffee-ln CPT Decaffeinated coffee mean (standard error) = 0.0793 (0.1139)]. We conclude that a single cup of coffee (100 mg caffeine) had no detectable effect on TENS outcome. Reasons why coffee did not produce a detectable effect on pain threshold are discussed.