Valeant got an FDA green light for its psoriasis drug Siliq yesterday, but with a warning that it has been linked to suicidal thoughts.

The US regulator approved the injectable interleukin-17 (IL-17) inhibitor to treat adults with moderate-to-severe plaque psoriasis, noting that the drug should be used in patients who "have failed to respond, or have stopped responding to other systemic therapies".

Siliq's (brodalumab) labelling will include a black box warning that "suicidal ideation and behaviour, including completed suicides, have occurred in patients treated with Siliq during clinical trials", said the FDA, and will only available through a restricted access programme.

The approval comes after a three-month extension to the review period that was intended to allow Valeant and the FDA to agree a risk evaluation and mitigation strategy (REMS) to manage access to the drug and resolve the labelling issue.

That warning presents Valeant with a big challenge as it tries to compete against other IL-17 inhibitors, namely Novartis' Cosentyx (secukinumab) - which was first to market and achieved sales of $1.13bn last year - and Eli Lilly's recent entrant Taltz (ixekizumab) which was approved in the US last March.

Valeant bought Siliq from AstraZeneca (AZ) in 2015, paying $100m upfront for rights to the drug with another $170m in development and regulatory milestones and $175m more in the offing if it meets sales targets. That was a bargain price for a phase III asset and clearly factored in the risks associated with the drug.

AZ's decision to offload the programme came shortly after its former partner on the drug Amgen handed back rights to brodalumab on concerns that the suicidal ideation link would result in "restrictive labelling".

The REMS programme drawn up for brodalumab means the drug can only be prescribed by doctors who have been certified to do so, and who counsel patients about the suicidal ideation risk. Patients also have to sign an agreement indicating they will seek medical attention if they experience mood changes.

"Siliq users with a history of suicidality or depression had an increased incidence of suicidal ideation and behaviour compared to users without this history," said the FDA in a statement.

"A causal association between treatment with Siliq and increased risk of suicidal ideation and behaviour has not been established."