Holford's claim in "The New Optimum Nutrition Bible" that "AZT, the first prescribable anti-HIV drug, is potentially harmful, and proving less effective than vitamin C" has been criticised by Ben Goldacre. Goldacre writes that Holford based this conclusion on a non-clinical study where "you tip lots of vitamin C onto HIV-infected cells and measure a few things related to HIV replication". Goldacre notes that the paper does not compare vitamin C to AZT for efficacy. He argues that "Holford was guilty of at least incompetence in claiming that this study demonstrated vitamin C to be a better treatment than AZT." Prof David Colquhoun argues that Holford's "advocacy of vitamin C as better than conventional drugs to treat Aids is truly scary".