Can my 10 year old who weighs 155 pounds take an adult dose of tylenol (acetaminophen) if he has a fever?

Yes: In this case weight is more important than age in determining dose. But i advise against taking anything to lower fever unless he is miserable, as fever is a key aspect of how our bodies fight infections- our immune system works better and bacteria ; viruses have difficulty surviving high temps. Reducing fever sabotages your immune system and prolongs the infection! treat discomfort, not fever.