Muhammad Ali is known today as one of the most significant and celebrated sports figures of the 20th century —and no doubt the best boxer of all time. After his shocking 2016 death, investigators began looking into his medical past, trying to understand if his fighting career had anything to do with his declining health.

REELZ’s new docuseries, Autopsy: Muhammad Ali, gives fans an insight into the later boxer’s pill habits and the medicine overdose that may have killed him.

“If Muhammad Ali did have thyroid problems, then this could well be implicated in his death and it would definitely have impacted on his abilities as a boxer,” says Autopsy’s Dr. Michael Hunter in the show teaser.

As RadarOnline.com has learned, Ali’s longtime doctor prescribed him the drug Thyrolar for his alleged thyroid condition.

“Thyrolar, also known as Liotrix, is a treatment for an underactive thyroid,” explains Dr. Hunter. “Thyrolar supplements the output of the thyroid gland. It can have numerous side effects which include vomiting and muscle pain. It’s hard to get the dosage right, and excessive amounts can cause an accelerated heart rate.”

While he was on the medication, Ali told friends that he often took two or three times the recommended dose.

“He said ‘I thought if one was good, two would be better,’” admits Ali’s former friend, Tim Shanahan, in the clip.

According to Dr. Hunter, notes from Muhammed Ali’s records show that his thyroid problem may have been miss diagnosed.

“In preparation for his fights, Ali was also reportedly taking Diterix, which is a drug very similar to amphetamine — this is a major red flag,” concludes Hunter.

Autopsy: Muhammad Ali airs Sunday, April 1 at 8:00 ET / PT on REELZ.