Yesterday, North Korean Olympic shooter Kim Jong Su was stripped of silver and bronze medals after he tested positive for propranolol. The drug is prescribed for a variety of conditions, from high blood pressure to migraines.

You've heard of various doping drugs such as EPO, but why would an Olympian use propranolol? (It probably wasn't to treat a hangover, despite some myths about its use for that condition.)

For an answer, called cardiologist Sandeep Jauhar, author of Intern: A Doctor’s Initiation, and director of the Heart Failure Program at Long Island Jewish Hospital in New Hyde Park, N.Y. An edited transcript follows.

Tell me what propranolol is typically used for, and what it does.

Propranolol is a beta-blocker, so it blocks the action of adrenaline. Adrenaline is implicated in a number of effects on the body—high blood pressure and a fast heart beat, for example—so by blocking it, propranolol lowers blood pressure, and heart rate. Doctors often use it to treat patients with high blood pressure, and with heart disease, to keep the heart rate in a reasonable range and not tax the heart muscle, or have it use too much energy.

It’s also used to treat other conditions that are mediated by high adrenaline levels, such as tremor and performance anxiety. Beta-blockers don’t lower the anxiety level, but they lower manifestations of the anxiety, such as fast heart rate, sweating and tremor.

I understand it’s also used for treating migraines?

It is used for treating migraines in kids.

Why would an Olympics shooter want to use it?

Probably for some of the same things that I just mentioned. It’s used to combat stage fright, or performance anxiety, and tremor. From the next to nothing I know about this case, he wasn’t using it for a medical condition; it was for performance enhancement.

Doctors do prescribe it for people with tremor, for example elderly patients with essential tremor. That’s a medical condition. It sounds like the tremor this shooter was experiencing had more to do with enhanced performance than with any medical condition. So it’s reasonable to ask whether he had an unfair advantage.

Why propranolol and not another beta-blocker?

I’m not sure. It’s a nonselective beta blocker. There are two receptors for adrenaline in the body: beta 1 and beta 2. When beta 1 is blocked, the action of blocking is to lower heart rate and also to lower blood pressure. Beta 2 is found in tissue like breathing passages and blocking the beta 2 receptor can cause bronchoconstriction, which means breathing passages get too narrow to breathe easily. So you wouldn’t use these in patients with asthma.

Whether you need a nonselective one to treat stage fright, I’m not sure. My suspicion is there’s something about nonselective beta blockade.

What kinds of side effects might the shooter experience?

The main one is fatigue. Because adrenaline is so important a hormone for maintaining a sense of well-being, blocking its activity can cause fatigue and depression. You can also have flare-ups of asthma in susceptible people, and erectile dysfunction.

If you use one for awhile, you’re blocking the action of adrenaline, so the body compensates by increasing density of beta receptors. Your symptoms could get worse, in something called a rebound effect, but we don’t know how long he was taking propranolol.

Wait a second, I take a beta-blocker for high blood pressure. Does that mean I can't be an Olympic shooter?

No, Ivan, you can’t be an Olympic shooter, but that has nothing to do with the beta-blocker you’re taking.