As a rule of thumb, don't trust the packaging when it's going out of its way to assure you it won't cause some negative side effect. They have a massive conflict of interest because they want you to buy it, and more importantly they legally don't have to actually prove it's factual, the burden is on you the consumer to sue them and prove they're lying in court if you think that's the case, and they're well aware the vast majority of people don't have the time or resources to do that.

If an online source is telling you it will cause that side effect, I'd be inclined trust that more (assuming the site is reputable and they're not trying to promote a different product).