LAS VEGAS — A retired athlete will now have an increased barrier of entry back into the UFC, but those returning after being released will gain some leniency.

A fighter who has retired or left the UFC under his or her own accord will not be able to compete again for the promotion until he or she is entered into the USADA drug-testing pool for six months, per changes to the UFC anti-doping policy made available to MMA Fighting on Thursday. Previously, the rule had been a four-month period in the testing pool before an athlete could return to the Octagon.

The alteration is one of a handful made by the UFC and USADA to the UFC anti-doping policy, which will go into effect April 1. The full changes are expected to be announced officially Thursday afternoon.

“It’s been a successful first year-and-a-half for this program, but with that said we’re always looking for ways to strengthen it and make it more effective for all involved,” USADA spokesperson Ryan Madden said. “The policy updates announced today are a direct reflection of our experiences, and the feedback we’ve received – from both athletes and the UFC – all of which we believe will give further confidence to competitors that they can step into the Octagon, compete clean, and win.”

There are exceptions to the six-month rule. The UFC may grant an exemption in “exceptional circumstances or where the strict application of that rule would be manifestly unfair to an Athlete,” the policy states. The UFC famously waived four months of testing for the returning Brock Lesnar prior to UFC 200 under this language.

The old rule was also broader, encompassing those returning athletes who had been released by the UFC, rather than just those who left by choice. There are also new rules in place regarding those particular situations.

Athletes returning to the UFC after leaving through no choice of their own, and any athlete coming into the UFC for the first time, now must be in the testing pool for one month prior to returning to competition. However, those two rules are waived when a fighter is signed to be a replacement on a card “due to loss of eligibility, injury or other event not reasonably foreseeable to UFC.”

For example, UFC strawweight Angela Hill attempted to come back after being cut by the UFC in 2015 at UFC 207 in December. She was told she could not, because she had to be in the drug-testing pool for four months. The UFC eventually granted her a waiver after she had spent more than a month in the pool, because she had not left the promotion by choice before. Now, the UFC is codifying this provision.

The intent of the rule for returning athletes to be in the testing pool for a period of time before competing again is so that a fighter cannot retire, use performance-enhancing drugs or banned substances and then return to the Octagon quickly without adequate testing.

“The majority of these changes are athlete driven,” UFC vice president of athlete health and performance Jeff Novitzky told MMA Fighting. “Early on in this, we knew there had to be a balancing act between the strength and comprehensiveness of the program and the fairness to the athlete. Over the year and half, this program has been in existence, we have consistently encouraged feedback from fighters and camps about how to make this program stronger, more comprehensive and, just as importantly, fairer to the athletes. All of these changes are a result of that interaction and feedback from athletes and camps.”

Another interesting change to the UFC anti-doping policy has to do with the definition of “in competition.” Now under the UFC and USADA, the in-competition window will close upon a post-fight sample collection. If the sample is not collected within a reasonable amount of time, the in-competition window will close one hour after the fighter’s post-bout medical clearance. The start of the in-competition period is now noon the day before the scheduled fight.

The in-competition window issue popped up after UFC 202 when Nate Diaz admitted to vaping cannabidiol oil (CBD) at the post-fight press conference. Cannabinoids are prohibited in competition and USADA gave Diaz a public warning for the violation. Under these new rules, Diaz would not have been in violation of the UFC’s anti-doping policy since his post-fight drug-testing sample was already taken.

The procedure for when a new UFC fighter discloses or does not disclose the use of prohibited substances prior to signing with the UFC has also been altered. If a fighter does not disclose the use of a banned drug before signing with the UFC, and then tests positive for that drug, that fighter will face an anti-doping violation — even if the substance was ingested prior to his contract being signed.

If a fighter discloses the banned substance, he or she will not face an anti-doping violation, even if he or she fails a drug test for that drug. However, if a fighter discloses use of a banned substance prior to his or her UFC tenure or “has an established and verifiable history” of use, attempted use or possession, he or she must be in the drug-testing pool for at least six months before competing. USADA might also ask that fighter to provide a minimum of two negative samples before being allowed to enter the Octagon. None of that, of course, would apply if the athlete had a valid therapeutic use exemption (TUE) for the banned substance.

The policy changes also has an alteration to the provisional hearing process. If an athlete wants to challenge a provisional suspension, he or she can have a hearing via conference call with a single arbitrator. The arbitrator will determine whether or not USADA’s decision for a provisional suspension should be upheld by determining whether USADA has the probable cause to pursue an anti-doping violation charge. It will not be a full evidentiary hearing, as it was before.

Another policy point that drew criticism since the UFC brought USADA on board in July 2015 was the clause disallowing fighters from associating with others who have been sanctioned. The new changes have removed training partners from that rule.

(An earlier version of the story stated that the start of the in-competition window had not changed. It has. The clarification has been made to the article. Also, a previous version of the story said that fighters did not have provisional hearing prior to these new changes. They did, but the process has been slightly altered. The change is reflected in the current article. MMA Fighting regrets the errors.