system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is exercise that increases my heart rate considered good, but medication and narcotics that increase my heart rate are considered bad?
gpt
Doctor here.  Narcotics (opiates) do not typically increase the heart rate, but drugs like cocaine and meth do, as they cause a sympathetic surge (adrenaline rush).  Regarding cocaine, it not only causes an increased heart rate but it can cause your coronary arteries (the blood vessels to your heart) to constrict (squeeze), resulting in heart attacks due to not enough blood and oxygen getting to the cardiac tissue.  Additionally, cocaine has been shown to accelerate the process of atherosclerosis (plaque build-up inside arteries) which can lead to heart attacks as well.  In other words, you can make your 20 year old arteries look like those of a 60 year old.  

Additionally, with this surge comes an elevation in blood pressure, which can cause things like intracranial bleeding (head bleeds), aortic dissections (tears) and other not so fun things.

Regarding exercise, a temporary elevation is okay, to a degree, but you're increasing your heart rate while your blood pressure stays the same, or increases slightly.  You do not get the squeezing and constriction that cocaine can cause.  Additionally, over time, with exercise, your resting heart rate will decrease as the heart molds itself and becomes more efficient.  Your heart is essentially stronger as a result of exercise, so it needs to beat less frequently.

If anything, cocaine will make your heart weaker for the above mentioned reasons, which is the big difference.  Along with all the other bad stuff drugs can do.