Jameson felt guilty that Anne's life was plagued by his illness, and the Cerebus II process was the only way to relieve them both of the burden.  Unfortunately, Jameson never consulted Anne about it.  He never told her that he was taking the alien drugs until he was aboard the U.S.S. Enterprise in 2364, en route to negtiate a hostage situation on Mordan IV.  Governor Karnas of Mordan IV had requested that Jameson come immediately, but en route, Jameson baffled the Enterprise crew by gradually growing younger before their eyes.  Adamant that he meet Karnas in peak condition, Jameson had taken th rest of his rejuvenation dosage and all of Anne's at once in the hopes that he could rush the process.  It was working, though he was suffering severe attacks of pain.  Captain Jean-Luc Picard was puzzled -- why did Jameson risk an overdose just to meet Mordan's Governor Karnas?  What wasn't he telling?

The answer came all too fast.  Official Starfleet records stated that Jameson had successfully negotiated with Karnas for the lives of hostages forty-five years ago on Mordan IV, just before the planet broke out into civil war that lasted forty-five years.  The truth was that Jameson had partially caused that war.  He hadn't saved the hostages by diplomacy, he'd given in to Karnas' demands for weapons against his enemies.  Thinking of the Prime Directive, Jameson had then supplied the same weapons to the enemy tribe, hoping that the balance would create peace.  The opposite occured, and now Karnas was seeking revenge.  There were no hostages -- the negotiation scenario was just a ruse to get Jameson to Mordan IV.  That was why Jameson had taken his entire rejuvenation dosage before the mission -- he knew he'd have to fight for his life.

In the end, however, Karnas did not kill Jameson, even though he wanted to.  He could see that the rejuvenation drugs were doing that already.  In agony, Jameson died at the feet of his enemy, a victim of his own guilt.