Last week, the Supreme Court put three executions in Oklahoma on hold as it reviews the constitutionality of the state's death penalty protocol.

If the nation's top court strikes down Oklahoma's lethal injection procedure, what would it mean for the death penalty? We've asked the experts what you need to know.

What exactly is the Supreme Court reviewing?

The court is assessing Oklahoma's use of the drug midazolam, a sedative used in its three-drug lethal injection protocol. According to the Death Penalty Information Center, five states have used midazolam for their executions, and at least five other states have proposed using it.

In the wake of several botched executions in 2014 involving the drug, a group of death row inmates in Oklahoma filed a petition challenging the efficacy of midazolam to mitigate pain, which they claim would render the state's executions in violation of the Eighth Amendment's protection against "cruel and unusual" punishment.

"[Midazolam] doesn't guarantee that the prisoners will be insensate throughout the execution," said Eighth Amendment expert Megan McCracken from U.C. Berkeley School of Law's Death Penalty Clinic.

Legal experts are not the only ones with concerns about Oklahoma's drug protocol. Several anesthesiologists have expressed concern about using midazolam for executions. The drug is typically used in surgical procedures to sedate patients before they receive anesthesia. To sedate an average adult in surgery, a dose of midazolam is normally no more than 2 milligrams. State executioners, however, administer the drug in much greater quantities. During recent executions, about 500 milligrams have been used. 

Many medical experts have noted that little is known about how the body reacts at that dose.

"We don't know the effects of 500 milligrams of midazolam," said Dr. David Waisel, an anesthesiologist at the Boston Children's Hospital, an affiliate of Harvard Medical School. "We don't study it, and we don't use it clinically. They are experimenting."

Why did the Supreme Court agree to consider a challenge to lethal injection now?

The lethal injection landscape has been fraught with issues since 2011, when Hospira, the only American manufacturer of a key lethal injection drug, stopped its production in the midst of an international campaign by capital punishment opponents. The company's decision set off a scramble to find another supplier and ultimately another drug. 

In late 2013, Florida became the first state to execute an individual using midazolam, but it wasn't until April 2014 that concerns about midazolam became widespread. That month, Oklahoma botched the execution of prisoner Clayton Lockett. Despite receiving an injection of midazolam, Lockett groaned and writhed on the gurney for about 40 minutes until his death, witnesses reported.

"I think the Supreme Court would prefer not to have to get involved in the details of executions, but felt compelled to because of what happened last year," said Richard Dieter, executive director of the Death Penalty Information Center. "Something went really wrong, and somebody's got to monitor this thing or states will keep repeating it."

The Supreme Court is expected to hear the Oklahoma prisoners' case in April and make a final ruling by July. According to the Death Penalty Information Center, midazolam was used for at least 11 of 35 executions in 2014.

Is this the first time that the Supreme Court has weighed in on lethal injection?

No. The last time the court weighed in was seven years ago, when it upheld Kentucky's lethal injection protocol in the case Baze v. Rees.

According to McCracken, it's critical to look at what has changed since then. "In 2008, all of the states were using a very similar protocol--all the states were using the same three drugs," McCracken said. "Because some pharmaceutical companies have made their drugs unavailable for executions, the states have been changing their methods."

McCracken considers the botched executions a "consequence of using untested, untried combinations."

What happens if the court strikes down the lethal injection method?

It's possible that midazolam would no longer be used. Other drugs might take its place or Oklahoma might decide to use a single-drug protocol in place of the current three-drug cocktail.

"I don't think that the death penalty is going anywhere," said Michael Rushford, president of the Criminal Justice Legal Foundation.

Even if the court limits the use of lethal injection and states continue to face difficulty getting approved drugs, there are other methods that prisons could employ. Virginia lawmakers have already discussed bringing back the electric chair when the approved drugs are not readily available. Wyoming lawmakers have proposed allowing firing squads.

Death penalty experts doubt that such methods would become the primary protocol for execution. "States changed from hanging to electric chair because it was a modern, supposedly painless method of execution," said Dieter of the Death Penalty Information Center. "There has been a continuous attempt to make executions appear more palatable, humane, and modern."

Could this be the beginning of a larger trend moving away from the death penalty?

Not really. "The Supreme Court position is that if the death penalty is constitutional, some method of execution will be allowed," Dieter said. "But you have to try to do the best. You have to minimize the harm. You can't just use any drug that's on the shelf. It has to be something reputable that stands up to scrutiny. [The Supreme Court] is not going to narrow it so much that it makes it impossible."

The rate of executions across the United States, however, has decreased markedly over the past decade. Ten years ago 60 inmates were executed. In 2014, there were 35. Among the 32 states that allow the death penalty, only seven had executions in the past year.

"In many places in the U.S., the death penalty is at best a symbolic gesture," said Austin Sarat, Amherst professor and author of "Gruesome Spectacles: Botched Executions and America's Death Penalty".

Regardless of this downward trend, more than 3,000 people remain on death row in the United States.