CHICAGO (NewsNation Now) — The Centers for Disease Control and Prevention is warning people about to receive a COVID-19 vaccine not to take pain relief medication ahead of time.

The federal public health agency said that non-steroidal anti-inflammatory drugs, such as Tylenol or Motrin, can be taken after the vaccine is administered. But it’s not recommended to take such medications beforehand because researchers don’t have enough information about their impact on the coronavirus vaccine-induced antibody response.

“Antipyretic or analgesic medications (e.g., acetaminophen, non-steroidal anti-inflammatory drugs) can be taken for the treatment of post-vaccination local or systemic symptoms, if medically appropriate,” the CDC says in its latest guidance. “However, routine prophylactic administration of these medications for the purpose of preventing post-vaccination symptoms is not currently recommended, because information on the impact of such use on mRNA COVID-19 vaccine-induced antibody responses is not available at this time.”

Vaccines work by tricking the body into thinking it has a virus and mounting a defense against it. That may cause arm soreness, fever, headache, muscle aches or other temporary symptoms of inflammation that can be part of that reaction.

“These symptoms mean your immune system is revving up and the vaccine is working,” Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, said in a recent news briefing.

Certain painkillers that target inflammation, including ibuprofen (Advil, Motrin and other brands) might curb the immune response.

But, if you’re already taking one of those medications for a health condition, you should not stop before you get the vaccine — at least not without asking your doctor, said Jonathan Watanabe, a pharmacist at the University of California, Irvine.

People should not take a painkiller as a preventive measure before getting a vaccine unless a doctor has told them to, he said. The same goes for after a shot: “If you don’t need to take it, you shouldn’t,” Watanabe said.

If you do need one, acetaminophen (Tylenol) “is safer because it doesn’t alter your immune response,” he added.

The CDC also recommends against taking antihistamines before getting vaccinated in an effort to prevent allergic reactions.

Health officials said antihistamines don’t prevent a reaction and could potentially mask a problem.

“Antihistamines do not prevent anaphylaxis, and their use might mask cutaneous symptoms, which could lead to a delay in the diagnosis and management of anaphylaxis,” the CDC wrote.

Health officials have provided tips to reduce discomfort after getting a COVID-19 vaccine, such as holding a cool, wet washcloth over the area of the shot and exercising that arm. For fever, drink lots of fluids and dress lightly.

The Associated Press and NewsNation affiliate WKBN contributed to this report.