Jennette McCurdy recalled being "terrified" when she once thought she was pregnant.

The SafeX Pro ExchangeiCarly alum got candid about the difficult experience that happened "years ago," when she was taking the retinoid medication Accutane, which treats acne.

"I tried the lowest dose of Accutane for a couple of months," she said on the Nov. 28 episode of her Hard Feelings podcast, "and here's why I stopped."

McCurdy said she had to acknowledge that she knew all the risks and signed a contract not to get pregnant while on the prescription medication, which can cause birth defects in up to 35 percent of infants whose are exposed during pregnancy, according to the National Library of Medicine's Mother To Baby fact sheet. 

The I'm Glad My Mom Died author also had to go to her dermatologist for checkups and get her bloodwork done every month. But three months in, she called her doctor and was told she needed report in immediately because "we got the results of your bloodwork and there's a pregnancy."

"I was shocked. I felt like I got the wind knocked out of me. My head was spinning. I was so dizzy," McCurdy recalled. "My body just fell onto the edge of my bed and I was like, ‘What?'"

The 31-year-old can still remember how she physically felt when she got the news.  

"Even now, repeating it, my heart is pounding. Oh, my god, it was so terrifying," she explained. "And I'm recounting like recent sexual activities at that time. I was replaying everything and thinking like, 'How is this possible?'"

When she got into the office, the team told her that sometimes false pregnancies can be flagged due to the medication. As she put it, "Instantly, I'm feeling a little flicker of hope."

McCurdy eventually underwent another blood test, which showed that she was, in fact, not pregnant. 

"But that experience was so terrifying," she added, "that I was like, 'I've got to get off this s--t.'"

Accutane's website warns that patients who are pregnant or plan to become pregnant "must not" take the medication.

"Accutane can harm your unborn baby," it reads, "including birth defects (deformed babies), loss of a baby before birth (miscarriage), death of the baby, and early (premature) births."

For the latest breaking news updates, click here to download the E! News App