Effects of nicotine on levodopa (LD) metabolism: Did not increase the mean blood concentration of LD and may reduce LD absorption by 34%-60% in some patients. May decrease transport of LD through the levorotatory amino acid transporter and inhibit LD crossing the blood-brain barrier. May treat LD-induced allodynia. Effect of caffeine on levodopa metabolism: Coffee consumption followed by levodopa preparation may accelerate the latency of onset of LD in PD patients. Caffeine may enhance the efficacy of exercise in LD. Effect of low-intensity exercise on levodopa metabolism: There was a tendency to increase the blood concentration of LD after low-intensity exercise, but it was not statistically significant. Low-intensity exercise may lead to an increase in the LD blood concentration threshold required for onset of action.