More than 500 Canadian men feel they weren’t warned properly about a prescription baldness medication they say has left them impotent, even years after they stopped taking it.

Two class-action lawsuits, one in Ontario and one in British Columbia, have been filed against Merck Frosst Canada, makers of finasteride — the key ingredient used in Propecia, a hair loss drug, and Proscar, a prostate drug also used to treat baldness. The B.C. case was approved by the province’s supreme court this month.

Merck denies the claims and says it acted responsibly in all aspects of producing and marketing the drugs.

The plaintiffs argue Merck failed to warn them of lasting sexual dysfunction after stopping treatment, despite the product’s labels in Europe indicating a risk of “persistent erectile dysfunction after discontinuation of treatment” as far back as 2008.

While Canadian labels at the time listed sexual dysfunction as a rare side effect, they indicated it was resolved in men “who discontinued therapy.” A warning of persistent erectile dysfunction didn’t appear in Canada until November 2011.

“If they were telling men in Europe about this, but not Canadian men, then the drug company was applying a double standard,” said David Klein, whose firm launched both cases. “Knowing (the full side-effects), would you risk it? I’m 59 and I wouldn’t risk it. I’d rather be bald and so would most men.”

Sean Ramsaran, 26, was prescribed Propecia by his dermatologist in 2009 when he noticed his hair was thinning and now calls himself “a useless person.”

Four years later, he wonders why neither Merck nor Health Canada warned him of the drug’s risks sooner.

“I can’t get an erection no matter how I try,” said the Toronto resident, noting he quit the drug a year into treatment after his sex drive plummeted. “I’m seeing a psychiatrist for my depression. I have nightmares, flashbacks to experiences I had while on the drug with my girlfriend, not being able to do anything.”

Merck denies any failing in its monitoring of the drugs. “The company acted responsibly and appropriately with respect to Propecia and Proscar throughout the development, marketing and post-marketing monitoring of these medicines,” wrote spokeswoman Lainie Keller in an email. She added there is no scientific data showing the drugs cause persistent impotence after discontinuing use.

“Sexual dysfunction is unfortunately a common condition among men and caused by many different factors,” Keller wrote.

Conservative Sen. Kelvin Ogilvie said drugs like finasteride illustrate problems Health Canada can have in monitoring prescription drugs and warning Canadians about possible side effects after they hit the market.

“We’re very slow to get out instructions on revised use or safety of these drugs,” said Ogilvie, who recently released a Senate committee report on the issue. “The difference between 2008 and 2011 is three years.”

Health Canada “considers any new information that may be available” when a foreign regulator takes action on a drug, wrote spokesman William Wells in an email earlier this month. It then conducts an “independent review of all relevant information” before deciding to work “with the manufacturer to update product labeling.”

“Based on the available information, it is Health Canada’s position that the therapeutic benefits of Propecia outweigh their risks,” Wells added.

This week, Health Canada announced it plans to strengthen its system for collecting an analyzing reports of adverse drug reactions. Among the changes being considered is making the reporting mandatory for doctors and others.

Finasteride blocks the conversion of testosterone to the more potent sex steroid dihydrotestosterone, known for contributing to baldness.

Since arriving on the Canadian market in 1993, finasteride has been linked to 20 cases of erectile dysfunction, 14 cases of sexual dysfunction, 15 cases of depression and five cases of suicidal ideation in Health Canada’s adverse drug reaction database. Ogilvie’s Senate committee report found adverse reaction reports likely represent “1 to 5 per cent” of the total side effects experienced by patients in the real world.

Last year, Health Canada issued a warning that finasteride may be associated with an increased risk of developing high-grade prostate cancer.

Loading... Loading... Loading... Loading... Loading... Loading...

Dermatologist Dr. Jeff Donovan, a hair restoration specialist in Toronto, says he prescribes finasteride to patients many times per day. “Could there by permanent problems? It certainly is possible, but I think it’s really anyone’s guess right now.”

In a 2012 study, Dr. Michael Irwig, an assistant professor of medicine at George Washington University in Washington, D.C., examined 54 men experiencing finasteride-related side effects and found that 96 per cent of them continued experiencing sexual dysfunction more than a year after stopping treatment. Another study of 61 former users found that 44 per cent reported having suicidal thoughts.

“What’s scary is that this has had some persistent, possibly permanent, effect on these guys,” said Irwig. “Some of them haven’t taken the medicine for 10 years, and they’re still having the same problems.”

For these men, all attempts at reversing the effects — from sexual therapy to testosterone injections to Viagra pills — have failed.

“If I knew there was a sliver of a possibility I’d have permanent damage to a vital organ in my body, I definitely wouldn’t have taken the drug,” said Ramsaran. “I’d rather be bald and not have hair anywhere on my body.”