It could be. Low tostesterone is known to be a cause of low energy levels in men. I have been on Lupron for two years now and must admit that I have not had this side effect. This may be due to my regular exercise routine. It would help if your dad did some modest weight bearing exercise and some walking daily. He should also speak to his doctor about taking some diet supplements. I take B12 and that seems to really help. I have seen some articles that say no B12 with PCa but I take it anyway. You may want to do your own research.
Good luck to you and your dad.
Diagnosed 04/10/08 Age 58 at the time
Gleason 4 + 3
DRE palpable tumor on left side
100% of 12 cores positive for PCa range 35% to 85%
Bone scan clear and chest x ray clear
CT scan shows potential lymph node involvement in pelvic region
Started Casodex on May 2 and stopped on June 1, 2008
Lupron injection on May 15 and every four months for next two years
Started IMRT/IGRT on July 10, 2008. 45 treatments scheduled
First 25 to be full pelvic for a total dose of 45 Gray to lymph nodes.
Last 20 to prostate only. Total dose to prostate 81 Gray.
Completed IMRT/IGRT 09/11/08.
PSA 02/08 21.5 at diagnosis
PSA 07/08 .82 after 8 wks of hormones
PSA 10/08 .642 one month after completion of IMRT, 6 months hormone
PSA 03/09 .38 six months post radiation and nine months into hormones
PSA 06/09 .36 or .30 depending on who did the test
PSA 09/09 .33 one year after IMRT and 16 months into hormone