LOS ANGELES — A state ballot initiative meant to lower prescription drug prices for California faces an expected opponent: the pharmaceutical industry, which has spent almost $70 million to defeat it.

But concerns are also coming from a more curious source: some patient advocacy groups.

Called the Drug Price Relief Act, or Proposition 61, the proposal would prohibit state programs, such as California’s Medicaid, from paying more for a drug than the lowest price paid by the federal Department of Veterans Affairs, which typically receives big discounts.

It promises to be the most prominent measure in November’s election to deal directly with pharmaceutical prices. And because the effort is happening in California, the most populous state and a trendsetter, the approach could quickly spread to other states if it is approved.

Yet how much, if any, money would be saved is a matter of hot debate, highlighting the complicated world of drug pricing. In recent weeks, there has even been a nasty spat between some AIDS activists — who say the proposal might inadvertently lead to price increases — and Senator Bernie Sanders, the Democratic presidential hopeful, who supports the measure.