While smoking, and for about an hour afterward, marijuana has proven to increase heart rate, blood pressure, and subsequently heart attack risk. These effects are also dose dependent — meaning the more marijuana used, the greater the effects on the cardiovascular system.
But that in and of itself is unlikely to affect your workout — if you're healthy.
"The consensus of the available data at this time indicates that cannabis use alone fails to present a significant health risk to otherwise healthy subjects," Paul Armentano, the deputy director of NORML, told Healthline.
That opinion was also supported by Dr. Kenneth Mukamal, an associate professor of medicine at Harvard University.
"These effects could be dangerous during exercise, but the evidence mostly comes from people with existing heart disease," he said.
So, depending on your current health, fitness level, and exercise goals, the risks of using marijuana are likely to change significantly.
"Our best guess is that marijuana smoking is particularly risky for people at high risk for heart disease. The higher one's underlying risk due to age, blood pressure, diabetes, etc., the higher the potential risk from marijuana," said Mukamal.
But even for healthy individuals, changes in blood pressure during intense workouts can lead to dizziness and falling.