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Former "Ultimate Fighter" competitor and current Invicta FC champion Angela Hill was ready to return to the UFC for a matchup against No. 5 ranked strawweight contender Jessica Andrade until she was ruled ineligible due to the company's anti-doping policy.

Because Hill was previously under contract with the UFC, she was required to undergo four months of testing from USADA (United States Anti-Doping Agency) before being allowed to re-enter the promotion.

The rule from the UFC's anti-doping policy reads as follows:

Hill wasn't the first fighter to re-sign with the UFC that had to undergo the four months of testing. Ben Saunders left the UFC for one fight and then re-signed with the promotion but was still required to go through the additional drug testing because of his exit from the organization for a period of time.

Former heavyweight champion Brock Lesnar was granted an exemption when he returned to action at UFC 200 in July after he signed to fight on late notice following negotiations with his employers at WWE to retain his services for the bout. Unfortunately, Lesnar failed a pair of drug tests that ended with his bout against Mark Hunt being ruled a no-contest before he was ultimately suspended for one year for the infraction.

Jeff Novitzky, the UFC vice president of health and performance, spoke to FOX Sports on Wednesday to further explain the rule and how the promotion determines who receives the exemption under the guidelines from the anti-doping policy.

"As the wording of the policy goes, any fighter that ceases to have a contractual obligation with the UFC, so had a contract and ceases (to have a contract), as the rule reads now by any means or methods. Whether it's being cut by the UFC or a decision on behalf of the athlete. The athlete has to be re-signed or unretired, they have to be back in the program for a period of four months," Novitzky said. "The UFC does have the ability to waive that as we did in the case of Brock Lesnar, if, and I think the wording is it would be manifestly unfair to the athlete.

"So in the case of Angela (Hill), we didn't feel based on several factors including the amount of time that she would have been back in the program, we didn't feel that it met that criteria. So she wasn't granted that waiver."

FOX Sports initially reported on December 7 that Hill had verbally accepted the match with Andrade for the event taking place on Dec. 30, but no contracts had been signed for her to return at that point. Lesnar inked his deal and then announced his return on June 6, which was more than a month from UFC 200 on July 9.

Novitzky says that the UFC examines the exemptions individually with discussions inside the promotion as well as involving USADA, who handles the testing and enforces the anti-doping policy.

"It is absolutely on a case by case basis," Novitzky said. "There is an internal discussion in the UFC and then we also have that discussion with USADA to make sure they're comfortable on it. So that is exactly what had happened."

It's impossible to ignore the backlash that the UFC received after granting Lesnar an exemption only to see him fail a drug test surrounding his fight with Hunt at UFC 200. Since that time, the UFC has made no public exemptions from the four-month testing policy that involves fighters returning to the promotion.

The good news is according to Novitzky, the UFC and USADA are currently discussing some changes that may be made to the anti-doping policy for 2017 and examining the details around the four-month testing rule is one under particular scrutiny right now.

"We have for the past couple of months been going through the policy, as it's been up and running for about a year and a half, looking at individual things that came up. Definitely this situation is one of them, the four month rule and retiring or ceasing to have a contractual obligation with the UFC," Novitzky said. "We're in the final stages of examining the policy really with a fine tooth comb. While I can't say definitively yet what if anything is going to be changed, if things are going to be changed it will happen before the end of this year.

"It will be publicly posted per the policy and there will be a 30 day lag time between the public posting and it going into effect. That lag time would be to give all the stakeholders a chance to see what the changes would be. Maybe we're not thinking things through properly and someone comes through to us and says 'do you realize what this is going to mean to the policy?' so it gives them that chance. The four month rule is definitely one that we're considering changing and taking a very close look at as we come close to tweaking the policy."

Novitzky takes pride in knowing that the UFC's anti-doping policy is the toughest and most thorough program in all of professional sports, but that doesn't mean he's opposed to change if that's going to make it better for everybody involved.

"When we put this program together, I came on in April 2015, I knew based on what I saw in my background and experience that this was going to be the most comprehensive program in professional sports. By far, not even a close second," Novitzky said.

"When you combine that with the very unique business model of the UFC with athletes coming in and coming out, 500 plus of them, independent contractors spread across I think 37 countries, we knew as careful as we were and as many scenarios as we could go through in our heads in those two months we put this thing together, we knew once this thing is up and running and is implemented we're going to run into scenarios where things could be tweaked to make them clearer."

That's why Novitzky says talks are ongoing internally with the UFC and USADA to potentially make some changes to the anti-doping policy because the program is there to benefit the fighters as much as meant to clean up the sport as a whole.

"As I tell everybody, the comprehensiveness of a program, how robust it is, that's super important beside the fairness of the program and the perception of fairness to the athletes is just as important," Novitzky said. "When issues come up like this and there is some uncertainty, if there's a change that can be made to make things a little more certain, we're certainly going to look at that.

"I think it's just as important to get the trust of the athletes in terms of the effectiveness of the program."