Which of the Following Best Describes the Evidence Regarding Concurrent

Which of the following best describes the evidence regarding concurrent use of caffeine and TENS for pain modulation?

A) Caffeine consumption may decrease the effectiveness of TENS.
B) Caffeine consumption increases the analgesic effect of TENS.
C) Concurrent use of caffeine and TENS may result in analgesic tolerance.
D) Caffeine acts as a competitive agonist on the opioid receptors, thereby increasing the analgesic effect of TENS.