The world’s largest health-care company says U.S. patients may avoid buying their medications if they see the prices in television ads.

A proposal from the Trump administration that would force drugmakers to disclose the list price of any medication that costs more than $35 could discourage some from seeking treatment, executives from Johnson & Johnson said on an earnings conference call Oct. 16.

List prices on TV ads “could be somewhat confusing and actually act as a deterrent to good,...