If Martin Shkreli, the young hedge fundmanager-turned-pharmaceutical executive who made news last month byjacking up the price of a life-saving medication by 5,000 percent,was surprised by the scorn his decision provoked, it was becausehis behavior was rather common.

That's according to an analysis released by Hedge Clippers, anactivist group that exposes what it views as predatory behavior byHedge Fund managers. In its report, the group points to evidencethat hedge funds and private equity firms have been the drivingforce behind exponential increases in drug prices.

"Out of the twenty-five drugs with the fastest-rising pricesover the past two years, twenty are owned or have been acquired byfirms with significant activity from hedge fund, private equity, orventure capital firms," said the group in a report.

The 25 medications the group identifies were all subject toprice increases of over 400 percent in the past two years, whilethree rose by over 1,000 percent.

At the top of the list was Vimovo, an arthritis drug. In 2013, a500/20 mg tablet cost $1.88. But since the drug was purchased byHorizon Pharmaceuticals that year, the price has risen more than1,200 percent, to $23.86 per tablet. According to the New York Times, that means the cost of theaverage daily treatment has risen from $4 to $50.

Horizon has defended itself, saying that the high prices wereaimed at recouping the multi-million investment it put intopurchasing the medication. It has further argued that out-of-pocketcosts for patients aren't nearly as high as the price wouldindicate; they typically negotiate discount rates for insurers.

Read: Worry over who gets $15,000 drug

Next on the list is Dutoprol, a medicine for high bloodpressure, currently owned by Concordia Healthcare Partners, whichpurchased it in April from a group of private equity investors. Inthe past two years, the price has increased from 52 cents per pillto $5.26, a 1,013 percent increase.

A recurring name on the list is Pershing Square Capital, a majorNew York hedge fund. It was involved in 13 of the 25 drugs on thelist because of its large stake in Allergan, the maker of a numberof drugs, ranging from botox to medicine for renal failure anddegenerative muscle disorders.

Pershing pushed for a hostile takeover of Allergan by acompeting firm, Valeant. Although it was ultimately unsuccessful— Allergan was instead taken over by Actavis — HedgeClippers argues that the bidding war drove up prices and madePershing CEO Bill Ackman big profits at the expense ofconsumers.

"(H)is manipulative moves exploded prices for medications neededby ordinary Americans — Americans who aren’t billionaires, andwho can’t afford to pay billionaire prices for their medications,"wrote Hedge Clippers.