Dr. Navindra Persaud has been fighting for four years to get access to thousands of pages of drug industry documents being held by Health Canada.

He finally received the material a few weeks ago, but now he's being prevented from revealing what he has discovered.

That's because Health Canada required him to sign a confidentiality agreement, and has threatened him with legal action if he breaks it.

The documents contain unpublished clinical trial data about the popular morning sickness drug, Diclectin, which Health Canada considers confidential business information.

Dr. Persaud wants to make unpublished clinical trial data public to evaluate the effectiveness of a morning sickness pill. (CBC) He's also been instructed to destroy the documents after he's reviewed them and to notify Health Canada in writing that the documents have been destroyed.

The confidentiality agreement also contains an indemnity clause that states Dr. Persaud, at his own cost, shall "save harmless Health Canada from and against all claims," including lawsuits, that arise out of any breach in the agreement.

"The situation seems upside down to me," said Dr. Persaud, a family doctor at St. Michael's Hospital in downtown Toronto.

"I'm trying to find out if the medication is safe and effective and Health Canada is the regulator. So they might actually want to facilitate this sort of research that I am doing. Instead, Health Canada has threatened me with legal action if I share the information."

Diclectin is a combination of an antihistamine and a form of vitamin B, recommended as a first-line treatment for nausea and vomiting in pregnancy, and it is prescribed to thousands of Canadian women every year.

I think it's fair for me to say today that I'm concerned the medication is not effective at all. - Dr. Navindra Persaud

Dr. Persaud said his concerns are about efficacy rather than safety. He has long questioned whether Diclectin works better than a placebo sugar pill, or better than Vitamin B6 alone.

After seeking legal advice, Dr. Persaud can only say that after seeing the data, his opinion of the efficacy of the drug has changed.

"I've gone on the record questioning how effective the medication was before," he said. "I think it's fair for me to say today that I'm concerned the medication is not effective at all."

The company, Quebec-based Duchesnay Inc., said that it "stands behind its product." In an email to CBC News, Duchesnay said,"Diclectin is the only proven safe and effective treatment approved by Health Canada for the treatment of nausea and vomiting of pregnancy."

Health Canada has given Duchesnay copies of the confidentiality agreement as well as copies of the documents released to Dr. Persaud.

"Any questions pertaining to this decision should be discussed with Health Canada," Duchesnay communications manager Ron Vaillancourt said in the email.

An earlier request for information was heavily redacted. (CBC) Health Canada said in an email to CBC that "this information was submitted over the years to Health Canada with an expectation that Health Canada would maintain its confidentiality."

Dr. Persaud began fighting for access to this information in 2011, under the federal Access to Information Act. The first documents he received were heavily redacted, including one page with the heading "adverse events" that was completely blank.

Earlier this year, he resubmitted his request for the material, under the new Protecting Canadians from Unsafe Drugs Act, also called "Vanessa's Law."

Health Canada said the act grants it the authority to disclose confidential business information to certain people for specific purposes, and that requesters are made aware that they are required to sign a confidentiality agreement.

Dr. Persaud said Health Canada knew he wanted the material for research that he intends to make public.

"I have had to seek legal advice and that in itself I believe is a deterrent to doing this sort of research that should not be in place," said Dr. Persaud.

This is essentially sending a message of chill. - Duff Conacher, Democracy Watch

He is trying to amend the agreement so he can share the data with colleagues, with the ultimate goal of publishing a review of the data in a peer-reviewed medical journal.

In the meantime, Dr. Persaud said he has shared his concerns about the lack of efficacy with both Health Canada and Duchesnay. He is also waiting for more information, including Health Canada's internal assessment of the confidential clinical trial data.

"It's just bizarre for Health Canada to say, here's the information that you want, but you're not allowed to tell anyone," said Duff Conacher, co-ordinator of Democracy Watch, a watchdog on open government.

"This is essentially sending a message of chill," he said.

"Health Canada is setting up a system to silence critics of drug companies and protect big company profits and protect them from accountability, instead of doing what they're supposed to be doing, which is protecting the public from harm," he said.

Diclectin has been approved in Canada since the late 1970s. In 2013, the U.S. Food and Drug Administration gave its approval of the drug for use in pregnant women with nausea and vomiting who do not respond after making lifestyle and dietary changes.

In August, the drug made headlines after U.S. socialite Kim Kardashian posted a positive review of the drug on social media, prompting a warning letter to Duchesnay from the FDA, about violations in U.S. drug promotion rules.

Duchesnay USA released this comment in response to the FDA letter:

"We are taking quick action in responding to the [U.S.] Food and Drug Administration's warning letter and immediately and effectively address any issues."

Diclectin is sold under the brand name Diclegis in the U.S.