Britney Spears' Medications Triggered Her Mental Health Crisis

Britney Spears is at the tail end of her 30-day stay at a mental health facility ... and we've learned more about how she landed there in the first place.

As we reported, Britney has had a rough time dealing with her dad's recent illness. Jamie and Britney are super close -- he's been her conservator for nearly a dozen years -- and his health battles have taken a big toll on her.

We're told at the same time, Britney's doctors were adjusting her meds which had lost their efficacy. Britney's mental health issues were stabilized with a cocktail of medicines that were designed specifically her. Over time, those meds were increasingly ineffective and doctors needed to create a new cocktail.

We're told there were problems. First, they had to wean Britney off the existing meds. This cannot be done quickly and there's a risk of suicide if it's not done right -- it's that serious.

As doctors weaned her off the meds, they created a new cocktail, but it's all trial and error, and there were errors that made Britney unstable and ultimately unwilling to cooperate with doctors.

She was admitted to the mental health facility and we're told doctors think they've now found the right mixture of drugs.

Britney got a day pass Sunday to spend time with her boyfriend, Sam Asghari, in Bev Hills. She went back to the facility the same day.

One other thing ... there have been reports the conservatorship has forced meds on Britney against her will. Not true. The conservatorship Britney is under does not permit the conservator to force drugs on the person for whom the conservatorship was created.

On that note, there have also been reports Jamie Spears forced Britney into the mental health facility. The type of conservatorship Britney has -- through the probate court -- does not allow a conservator to force someone into a mental health facility.

What's more, we're told Jamie is adamant -- he did not want his daughter to go to the facility because he thought it would leak out to the media and he felt there were better ways of solving her problems. We're told Britney is the one who said she wanted to go.