President Bush says he's feeling a lot better after a bout of exhaustion tied to his thyroid disorder.

"Today's really the best I've felt since the onset of all this problem," a thinner Bush told reporters on Wednesday.Bush said he had lost 10 pounds in the past three weeks and now weighs 187, his lowest weight in 30 years.

He has been tiring easily and has been taking rest breaks during his work day in the study off the Oval Office, said spokesman Marlin Fitzwater.

The president said he had recovered by Wednesday from being "dead tired" during Tuesday's busy schedule with visiting Queen Elizabeth II.

Bush was diagnosed last week with Graves' disease, an immune system disorder that caused him to suffer an irregular heartbeat while jogging on May 4.

He is taking drugs to regulate the heart and thin his blood.

The medicine is rendering his thyroid inactive, and that is sapping his energy, Fitzwater said. Bush is expected to feel somewhat fatigued for another week to three weeks, the spokesman added.