Researchers analysed survey data from 2001 to 2013 in which around 1000 US adults a year were asked if they found animal testing morally acceptable or wrong.
The results showed that last year, 41% of those questioned thought medical experiments on animals were morally wrong - 12% more than in 2001.
A more dramatic change was seen in the opinion of younger adults. Among participants aged 18 to 29, 54% were opposed to animal testing in 2013, an increase of 23% since 12 years earlier.
Women also tended to be more unhappy about animal experiments, with 52% last year saying it was morally wrong, a rise of 16% since 2001. Just under a third of men and a third of all adults aged over 30 were opposed to medical testing in 2013.