A bestselling author has shared a heartbreaking story about how a popular hair loss drug led to the demise of her ex-husband’s sexual function — and their marriage.

Speaking recently on the podcast “Moral Medicine,” Thammika Songkaeo said she noticed they had no love life to speak of while they were still dating.

Her then-boyfriend told her that it was because he had taken Propecia — the brand name of finasteride, which is commonly used to treat hair loss in men. One of the potential side effects is sexual dysfunction.

At the time, she thought it was just a temporary issue — or that it would only be a problem intermittently.

“I did not at all realize that it was permanent, serious [and] devastating,” she said.

They got married and stayed together for seven years, with Songkaeo convincing her ex to take an erectile dysfunction drug to improve intimacy.

The couple welcomed a daughter, but Songkaeo’s loneliness worsened.

Ultimately, she decided to walk away from the sex-starved marriage.

Noting that her ex was a wonderful partner outside of the bedroom, they remained great friends — and Songkaeo went on to write a novel about her experience, “Stamford Hospital,” which became a No. 1 bestseller on Amazon Singapore.

Now, she’s trying to spread the word not only about how post-finasteride syndrome (PFS) — a condition in which someone experiences severe side effects after they stop using finasteride — affects its victims, but also the ones they love.

“The depth of the loneliness I felt was to the point where I, myself, was becoming suicidal or having suicidal thoughts,” Songkaeo said.

“I had to call the suicide hotline because it became that bad for me — and, usually, I’m a pretty happy person.”

She questions the ethics of distributing a drug that can have such potentially devastating consequences.

“Finasteride has the capacity to dissolve one person so much that it becomes this domino effect…there’s just so much destruction around it — and it feels like unnecessary destruction,” she said.

Songkaeo was interviewed by podcast host Mark Millich, who made headlines earlier this year by telling the Wall Street Journal that he experienced debilitating side effects after buying finasteride.

Some of his side effects included anxiety, dizziness and slurred speech. His sex drive also plummeted, and his genitals shrank and changed shape.

Millich previously interviewed a 28-year-old man who reported a roller coaster of side effects due to PFS, including sexual dysfunction, insomnia, severe weight and muscle loss, skin rashes and pelvic pain.

“Every month, I feel like there’s a new side effect,” the man said. “It’s really changed my life completely.”

In April, the US Food and Drug Administration issued a warning about topical finasteride products distributed by telehealth companies, citing several reports of adverse events such as erectile dysfunction, anxiety, suicidal ideation, brain fog, depression, fatigue, insomnia, decreased libido and testicular pain.

If you are struggling with suicidal thoughts or are experiencing a mental health crisis and live in New York City, you can call 1-888-NYC-WELL for free and confidential crisis counseling. If you live outside the five boroughs, you can dial the 24/7 National Suicide Prevention hotline at 988 or go to SuicidePreventionLifeline.org.