Mo Farah has withdrawn from Sunday's 1,500m race at the Diamond League meeting in Birmingham.
In a statement, the two times Olympic gold medallist said: "This week has been very stressful and taken a lot out of me.
"I have not been able to focus properly on today's race and after the events of the last few days feel emotionally and physically drained.
"I want to run well in the IAAF World Athletics Championships in Beijing and have decided it is better for me to go back to the US, seek answers to my questions and get back into training.
"I apologise to the people who bought tickets to come and watch me race and ask for your understanding at this time."
On Saturday, Farah told reporters that he was "angry" his name had been "dragged through the mud" after allegations that his coach, Alberto Salazar, was involved in doping.
The Olympic gold medallist said that he is "emotionally and physically drained".
The report alleged that Salazar doped US 10,000-metre record holder, and Mo Farah's training partner, Galen Rupp in 2002.
There were no claims made in a BBC documentary of any wrongdoing by Farah.
Salazar and Rupp deny allegations of involvement in doping.
A Saturday's press conference, Farah said that he would stick with the American coach until he saw the evidence against him.
"I have spoken to him and said, 'What's going on?' I said I need answers and he said, 'Mo, I can prove to you, these are just allegations.'"
Farah said he wanted further assurances "as soon as possible."
The 5,000 and 10,000 metre gold medalist at the London 2012 Olympics said the allegations had "affected" him before the race he was scheduled to run today.
"My reputation is getting ruined. You guys are killing me," he told a news conference. "I'm a clean athlete. I'm against drugs 100% and believe anyone caught should be banned for life."