The Advertising Standards Authority has rejected complaints that an Alzheimer's Research UK TV advert was unjustifiably distressing.
The advert, which showed an apparently drowning baby with a tear in its eye, generated 25 complaints.
Alzheimer's Research UK first broadcast the advert on 20 September as part of its five-week Make Breakthroughs Possible campaign.
Made by the creative agency AMV BBDO, it appeared on TV and social media, and in cinemas, and reached more than 10 million people. It is available on YouTube.
The ASA ruling said: "While we acknowledged that some viewers might find the initial images disconcerting, we considered that the effect was proportionate given the serious nature of the issues covered by the ad.
"Furthermore, the baby did not appear distressed and the context of the images was made clear in the course of the ad.
"We did not consider that the ad was likely to cause unjustifiable distress to viewers."
Alzheimer’s Research UK said the advert challenged the prevailing sense of fatalism that nothing could be done about dementia.
A spokesman for the charity told Third Sector it was "pleased and reassured" by the ruling.
He said the tension of the advert "was swiftly resolved with an ending that conveyed a clear message of survival and hope" and the content "was proportionate given the serious nature of the issues covered".
The spokesman added that the advert "drove some of the highest awareness of the charity and our work in our history" and might be used again on social media or in cinemas.
An ASA spokesman said 25 complaints "isn’t particularly high in the scheme of our work".
He said: "We'd be looking at three or four-figure complaint numbers for it to rank in the 'most-complained-about' category."
The ASA last year rejected dozens of complaints against an ARUK advert in which Santa was portrayed as having dementia.
The charity’s voluntary income rose by 44 per cent last year.