Suppose there is a rare, horrible disease called X. On average, the disease afflicts 4 people in a million in a lifetime. 4 in a million or 0.0004 are both ways of expressing the absolute risk a person has of getting X. A tiny risk and you wouldn't worry about it under normal circumstances.
Suppose your risk of getting X can be reduced by 75% by using a special, expensive toothpaste for your entire life. Reduce 4 by 75% and it reduces to 1. If you use this toothpaste for life, the absolute risk of getting disease X in a lifetime falls from 4 in a million to 1 in a million.
If a pharma company told you that your absolute risk of getting disease X was 4 in a million spread over your entire lifetime, and you could reduce the risk to 1 in a million, would you be impressed? Would you care? Would you be inclined to buy the toothpaste? I certainly wouldn't. So pharma companies in this situation would never mention absolute risk of getting such a disease.
But if you were not told the absolute risk of getting the disease, and instead were just told the reduction in risk is 75% when using the toothpaste for life, then if X is particularly scary you might be inclined to buy it. Because a 75% reduction in risk sounds HUGE. But the reduction is a relative risk, not an absolute risk.
When pharma companies or doctors mention risk they rarely tell you the absolute risk they usually mention relative risk. And they don't tell you they are using relative risk reduction, they just use the phrase "risk reduction". According to Dr Kendrick in his book Doctoring Data surveys have shown that doctors are no better at working out what is absolute risk, what is relative risk, and what the difference is than the public is.
It is also standard policy to use absolute risk when mentioning risks of a treatment because they sound small, but when mentioning benefits they use relative risk because they sound huge. And none of these switches from absolute to relative and back again are highlighted or made clear. Even Dr Kendrick has mentioned that it is often very difficult to work out absolute risks of something happening, and is often difficult or impossible to work out which type of risk is being used.
Another thing that is frequently done is to quote statistics for different periods of time. So you might be told an absolute risk reduction over a year rather than a lifetime risk. (Your absolute risk of getting a cold in a single year is a lot lower than the absolute risk of getting a cold in your lifetime.)
Pharma companies and scientists writing papers will use every trick they can think of to make you think their drug or their research is relevant and important. And they have all sorts of ways of pulling the wool over your eyes. They can mention relative risks of side effects while mentioning a competitor's product, and mention only absolute risks of side effects when mentioning their own. And you probably won't know they have done this.