The combination of ephedra and caffeine increases hypersensitive response before, during and after exercise, and increases systolic blood pressure before exercise. That higher rate pressure results in more work for the heart.
The findings were presented at the Experimental Biology meeting in San Diego, which runs April 11-15.
The study included five men and five women who were given either 150 milligrams of caffeine and 20 milligramsof ephedra or a placebo. They were then monitored while at rest, during exercise and after exercise.
The people who took the caffeine/ephedra had higher hypertensive response after 60 minutes of rest. That response remained higher at 30 and 60 minutes of exercise. The people who took the caffeine/ephedra also had higher systolic blood pressure while they were resting and had higher mean arterial pressure.
Ephedra is a controversial herb marketed as an energy booster and weight loss aid. It's been linked to almost 100 deaths, including high school, college and professional athletes who have collapsed during games or practice.
Here's where you can learn more about ephedra.