Louisiana could become the first state to classify abortion pills as dangerous controlled substances, making possession of the pills without a prescription a crime subject to jail time and fines.

A bill that would designate the abortion pills mifepristone and misoprostol as Schedule IV drugs — a category of medicines with the potential for abuse or dependence — passed the state’s Republican-controlled House of Representatives on Tuesday by a vote of 63 to 29. Should the Senate follow suit, Gov. Jeff Landry, a Republican and a vocal opponent of abortion, is likely to sign the legislation into law.

The measure — which would put abortion pills in the same category as Xanax, Ambien and Valium — contradicts the way the federal government classifies mifepristone and misoprostol. The federal Food and Drug Administration does not consider abortion pills to be drugs with the potential for dependence or abuse, and decades of medical studies have found both to be overwhelmingly safe.

Under the legislation, possession of mifepristone or misoprostol without a prescription in Louisiana could be punishable with thousands of dollars in fines and up to five years in jail. Pregnant women would be exempt from those penalties; most abortion bans and restrictions do not punish pregnant women because most voters oppose doing so.

“These drugs are increasingly being shipped from outside our state and country to women and girls in our state,” Attorney General Liz Murrill, a Republican, said in a statement on social media. “This legislation does NOT prohibit these drugs from being prescribed and dispensed in Louisiana for legal and legitimate reasons.”

Louisiana already bans most abortions, except when women’s lives or health are in danger or fetuses have some fatal conditions. As a result, abortion rights advocates and legal scholars said that in practice, the measure might not prevent many abortions among Louisiana women. Since the state imposed its strict abortion ban after the Supreme Court overturned Roe v. Wade, many patients have traveled to states where abortion is legal or have obtained pills under shield laws from doctors or nurses in other states who prescribe and mail the medications to Louisiana. Such circumstances would not be affected by the new bill, experts say.

“The most important part of this probably, from the anti-abortion standpoint, is making it seem like these drugs are unsafe and stigmatizing their use, possession, acquisition — and trying to make it so that people in Louisiana who they know are getting pills online and others are just more reticent to do so,” said David S. Cohen, a law professor at Drexel University who supports abortion rights.

He said that those who might face penalties under the bill would be informal networks of volunteers who provide nonprescription pills to some communities, as well as women who are not pregnant but order abortion pills just in case.

The measure, supported by Louisiana Right to Life, an anti-abortion group, has infuriated hundreds of doctors and medical students in the state, who signed a letter opposing the bill. The doctors noted that mifepristone and misoprostol have many other medical uses. Misoprostol is commonly used to prevent ulcers and also to aid labor during childbirth, and both medications are used to help women experiencing miscarriages.

“Adding a safe, medically indicated drug for miscarriage management, prevention of ulcer, or to induce normal labor to a controlled substances schedule creates the false perception that these are dangerous drugs that require additional regulation,” the letter said. “Overall, this results in fear and confusion among patients, doctors, and pharmacists, which delays care and worsens outcomes,” the letter added.

Sarah Zagorski Jones, a spokeswoman for Louisiana Right to Life, said that the bill means “giving law enforcement more authority to stop the abuse of distribution of the pills on the streets and online.” The bill should not affect prescribing physicians or pregnant women who are not seeking an abortion but need the medication to deal with complications or labor, she added.

The proposal to reclassify the two medications in Louisiana was a late amendment to another bill that would criminalize forced abortions, creating a crime called “coerced criminal abortion by means of fraud.” Both the bill and the amendment were introduced by State Senator Thomas Pressly, a Shreveport Republican, after his sister’s husband pleaded guilty to secretly putting misoprostol in her cups of water in an unsuccessful attempt to end a pregnancy. (She gave birth, but the baby was born prematurely.)

In a statement in late April, when the bill was amended, Mr. Pressly said that it came after “trying to determine what other steps I can take to control the rampant illegal distribution of abortion-inducing drugs that ended up hurting my sister.”

“My sister’s story is clear proof that these drugs are being weaponized and are a risk to the public health,” he added. “By placing these drugs on the controlled substance list, we will assist law enforcement in protecting vulnerable women and unborn babies.”

Opponents of the measure said that the use of the medications for conditions like miscarriage and ulcer treatment may be more directly affected by the legislation than abortions would be.

“What we’re really worried about is that people are going to have this false idea that a drug ultimately is now dangerous and that their doctors are trying to poison them,” said Dr. Jennifer Avegno, the director of the New Orleans Health Department, who helped organize the letter opposing the measure.

Dr. Avegno, an emergency medicine physician, said that Schedule IV drugs impose certain logistical hurdles, such as extra steps for calling prescriptions into pharmacies or possibly needing paper prescriptions, which could cause delays. For example, she said, if a woman who is miscarrying on a weekend is bleeding heavily and needs misoprostol, the new bill might require her to visit a doctor and to obtain a paper prescription, forcing her to wait a day or two as her condition worsens.

Or, Dr. Avegno said, “imagine being in labor, and your O.B. says, ‘Oh, you need misoprostol to ripen your cervix so we can progress labor safely,’ and that woman thinks, Wait, why is she giving me the dangerous drug?”

Louisiana has already seen some confusion over its tough abortion laws, including an instance where a mother was denied an abortion because her baby had developed a fatal condition that was not explicitly listed as a medical exception.

Michelle Erenberg, executive director of Lift Louisiana, a reproductive rights organization, said that her group and others are exploring a possible legal challenge if the measure passes and said she had “concerns about this being replicated in other states.”

Abortion rights has proved to be a potent political issue for Democrats, and they were already using the Louisiana bill as election-year fodder. The Biden campaign held a briefing about the measure for journalists on Wednesday and sent out an email, saying “Trump Did This: Louisiana MAGA Republicans Vote to Criminalize Possession of Abortion Medication.”

But in Louisiana, there appears to be little indication that a broad swath of the state’s electorate will turn against state lawmakers for their continued efforts to curb abortion access. In his previous role as attorney general, Gov. Landry repeatedly defended the state’s abortion ban in court before overwhelmingly winning his race for governor last year.

When Vice President Kamala Harris condemned the bill on social media as “absolutely unconscionable,” Mr. Landry shot back, saying her criticism meant that “you know you’re doing something right.”

He added: “This bill protects expectant mothers while also allowing these drugs to be prescribed to those with a valid prescription.”

And there are still a number of Democrats in Louisiana who oppose abortion and have won re-election in recent years. The state’s current abortion bans were signed into law by its former governor, John Bel Edwards, a conservative Democrat.

“I actually cannot think of a single legislative race where a Republican lost because of the abortion issue,” John Couvillon, a Republican pollster in Louisiana, said. “When we enacted some pretty stringent pro-life legislation with the help of a Democratic governor, it didn’t impact the election results at all,” he added.

Kitty Bennett contributed research.