DEAR DR. ROACH: Could you please explain the percentages that are given when a study indicates an increase for a particular risk? For example, say a person with mild coronary artery disease is at an increased risk of having a heart attack when taking certain drugs like meloxicam. It is confusing and possibly frightens a person away from beneficial therapy when there isn’t a full explanation of what these numbers mean.

— B.C.

ANSWER: Understanding worsening risks in a medical context can be challenging because advertisements often talk about relative risks, whereas most people understand absolute risks more intuitively.

In people with mild coronary artery disease (people who have blockages but have never had a heart attack), anti-inflammatory drugs like diclofenac increase the risk by 3 people per 1,000. So, if 1,000 people took diclofenac, we’d expect three more major vascular events (mostly heart attacks or strokes) than what would occur if they’d been taking a placebo pill without an active ingredient. This an absolute increase in risk of 0.3%, while the relative risk increase is about 40%. (Imagine this for the placebo group. Eight people per 1,000 got a heart attack or stroke, while in those who took the anti-inflammatory, 11 people per 1,000 got a heart attack or stroke.)

Both numbers are correct, but the relative risk increase sounds bigger and scarier. Another way of expressing the absolute risk for harm is figuring out the number of people who need to be harmed; in this case, about 333 people need to take the drug for a year to cause 1 person to get a heart attack or stroke.

In people who’ve already had a heart attack, the absolute risk increase is much higher — about a 10% increased absolute risk with 10 people who would need to be harmed. Long-term, daily anti-inflammatory medicine isn’t recommended in this group because of the high absolute risk.

I’ve had many patients who look at the data and decide against taking anti-inflammatory drugs, but I’ve also had a few decide that it was still worth it. Despite other options like acetaminophen, only anti-inflammatories relieved their symptoms sufficiently.

Even though an increased cardiovascular risk is probably present with all anti-inflammatory drugs, there do seem to be drugs that are at a higher risk and some that are at a lower risk. Low-dose ibuprofen and naproxen (both available over-the-counter) have a small effect on cardiovascular risk — considerably smaller than diclofenac.