Dopamine
RCT: Effect of single 100mg dose of levodopa (L-dopa) on sexual response in men and women
https://www.ncbi.nlm.nih.gov/pubmed/15470373
- Needs fuller review, but apparently this has no effect on penile girth!
Effects of levodopa on nocturnal penile tumescence: a preliminary study.
https://www.ncbi.nlm.nih.gov/pubmed/9796623
Reaction times
https://www.ncbi.nlm.nih.gov/pubmed/12185401