Stabilization Serums
-(noun): a series of medical injections which, among other things, retards the aging process; an invention of the Priest-Kings approved by them for use by humans; administered in 4 injections. 
Book 3: Priest-Kings of Gor, page 124
Book 5: Assassin of Gor, page 30 and 31
Book 7: Captive of Gor, pages 93 - 97
Book 11: Slave Girl of Gor, page 282 
Book 22: Dancer of Gor, pages 472-474

Old Age

The Player was a rather old man, extremely unusual on Gor, where the stabilization serums were developed centuries ago by the Caste of Physicians in Ko-ro-ba and Ar, and transmitted to the Physicians of other cities at several of the Sardar Fairs. Age on Gor interestingly, was regarded, and still is, by the Caste of Physicians as a disease, not an inevitable natural phenomenon. The fact that it seemed to be a universal disease did not disuade the caste from considering how it might be combated. Accordingly the research of centuries was turned to this end. Many other diseases, which presumably flourished centuries ago on Gor, tended to be neglected, as less dangerous and less universal than that of aging. A result tended to be that those susceptible to many diseases died and those less susceptible lived on, propagating their kind. One supposes something similar may have happened with the plagues of the Middle Ages on Earth. At any rate, disease is now almost unknown among the Gorean cities, with the exception of the dreaded Dar-Kosis.

Stabilization Serums

The Stabilization Serums, which are regarded as the right of all human beings, be they civilized or barbarian, friend or enemy, are administered in a series of injections, and the effect is, incredibly, an eventual, gradual transformation of certain genetic structures, resulting in indefinate cell replacement without pattern deterioration. These genetic alterations, moreover, are commonly capable of being transmitted. For example, though I received the series of injections when first I came to Gor many years ago I had been told by Physicians that they might, in my case, have been unnecessary, for I was the child of parents who, though of Earth, had been of Gor, and had received the serum. But different human beings respond differently to the Stabilization Serums, and the Serums are more effective with some than with others. With some the effect last indefinately, with others it wears off after but a few hundred years, with some the effect does not occur at all, with others tragically, the effect is not to stabilize the patteren but to hasten its degeneration. The odds, however, are in favor of the recipient, and there are few Goreans who, if it seems they need the Serum's do not avail themselves of them.
--Assassin of Gor pg 30 - 31

Statement of effectiveness of serums

Strangely, though it had now been six years since I left counter-earth, I can discover no signs of aging or physical alteration in my appearance. I have puzzled over this, trying to connect it with the mysterious letter, dated in the seventeenth century, ostensibly by my father, which I received in the blue envelope. Perhaps the serums of the Caste of Physicians so skilled on Gor, have something to do with this, but I cannot tell.
--Tarnsman of Gor pg 218 - 219

I had spent eight days in the slave pens, waiting the night of the sale. I had been examined medically, in detail, and had had administered to me, while I lay bound, helplessly, a series of painful shots, the purpose of which I did not understand. They were called the stabilization serums. We were also kept under harsh discipline, close confinement and given slave training. I well recalled the lesson which was constantly enforced upon us: "The master is all. Please him fully."
"What is the meaning of the stabilization serums?" I had asked Sucha. She had kissed me. 
"They will keep you much as you are," she said, "young and beautiful." I had looked at her, startled.
"The masters, and the free, of course, if there is need of it, you must understand, are also afforded serums of stabilization," she said adding, smiling, "though they are administered to them I suppose, with somewhat more respect than they are to a slave."
"If there is need of it?" I asked. 
"Yes " she said. 
"Do some not require the serum'?" I asked. 
"Some," said Sucha, "but these individuals are rare, and are the offspring of individuals who have had the serums." 
"Why is this?" I asked. 
"I do not know," said Sucha "Men differ." 
The matter, I supposed, was a function of genetic subtleties, and the nature of differing gametes. The serums of stabilization effected, it seemed, the genetic codes, perhaps altering or neutralizing certain messages of deterioration, providing, I supposed, processes in which an exchange of materials could take place while tissue and cell patterns remained relatively constant. Ageing was a physical process and, as such, was susceptible to alteration by phvsical means. All physical processes are theoretically, reversible. Entropy itself is presumably a moment in a cosmic rhythm. The physicians of Gor, it seemed, had addressed themselves to the conquest conquest of what had hitherto been a universal disease called on Gor the drying and withering disease, called on Earth, ageing. Generations, of intensive research and experimentation had taken place. At last a few physicians drawing upon the accumulated data to hundreds of investigators, had achieved the breakthrough, devising the first primitive stabilization serums, later to be developed and exquisitely refined. I had stood in the rage startled, trembling. 
"Why are serums of such value given to slaves?" I asked. 
"Are they of such value?" she asked "Yes," she said, 'I suppose so." She took them for granted, much as the humans of Earth might take for granted routine inoculations. She was unfamiliar with ageing. The alternative to the serums was not truly clear to her. 
"Why should slaves not be given the serums?" she asked. "Do the masters not want their slaves healthy and better able to serve them?"
--Slave Girl of Gor, page 282

Statement of effectiveness of serums

"You were English," I said. 
"Yes," he said, smiling. 
"Brought here on the Voyages of Acquisition?" 
"Of Course, he said."
[Skipping a line] "How long ago?," I asked. He began to try to stuff the tobacco into the bowl of the pipe. Given the gravitational alteration this was no easy task. 
"Do you know of these things?," asked Parp, without looking up. 
"I know of the Stabilization Serums," I said. 
Parp glanced up from the pipe, holding his thumb over the bowl to prevent the tobacco from floating out of it, and smiled. "Three centuries," he said, and then returned his attention to the pipe.
--Priest Kings of Gor pg. 288

Example of Serum effectiveness

"Torvald," said he, "sleeps in the Torvaldsberg, and has done so for a thousand years. He waits to be wakened. When his land needs him, he shall awake. He shall then lead us in battle. Again he will lead the men of the north."
[Skipping a line] "What is your true name?," I had inquired. He looked at me, and smiled. It was strange what he said. "My name," he said, "is Torvald." Then he had turned away, I watched him return to the mountain. I thought of the stabilization serums, My name is Torvald, he had said.
--Marauders of Gor pg. 232 & 294

Priest Kings and the Stabilization Serums

"From Sarm's point of view of course your utilization there was simply to curtail the spread of the Empire of Ar, for we prefer humans to dwell in isolated communities. It is better for observing their variations, from the scientific point of view, and it is safer for us if they remain disunited, for being rational they might develop a science, and being sub-rational it might be dangerous for us and for themselves if they did so."
"That is the reason then for your limitations of their weaponry and technology?" 
"Of Course," said Misk, "but we have allowed them to develop in many areas--in medicine, for example, where something approximating the Stabilization Serums has been independently developed."
"What is that?," I asked. 
"You have surely not failed to notice," said Misk, "that though you came to the Counter-Earth more than seven years ago you have undergone no significant physical alteration in that time." 
"I have noticed," I said, "and I wondered on this." 
"Of course," said Misk, "their serums are not as effective as ours and sometimes do not function, and sometimes the effect wears off after only a few hundred years."
--Priest Kings of Gor pg. 123-124

"You spoke of knowing the Cabots for four hundred years," I said. 
"Yes," said Misk, "and your father who is a brave and noble man, has served us upon occasion, though he dealt only, unknowingly, with Implanted Ones. He first came to Gor more than six hundred years ago."
"Impossible!," I cried. "Not with the stabilization serums," remarked Misk."
--Priest Kings of Gor pg. 126

Nature and Price of Serums

"In the first house of my slavery," I said, "I was given a series of injections. I am curious about them. Were they innoculations against disease?"
"I know those you mean," he said. "No, they were the stabilization serums. We give them even to slaves." 
"What are they?," I asked. 
"You do not know?,"  he asked. 
"No," I said. 
"They are a discovery of the caste of physicians," he said. "They work their effects on the body." 
"What is their purpose?," I asked. 
"Is there anything in particular which strikes you generally, statistically, about the population of Gor?," he asked. 
"Their vitality, their health, their youth," I said. 
"Those are consequences of the stabilization serums," he said. 
"I do not understand," I said. 
"You will retain your youth and beauty, curvaeous slave," he said. "That is the will of masters."
"I do not understand," I said frightened. 
"Ageing," he said, "is a physical process, like any other. It is, accordingly, accessible to physical influences. To be sure, it is a subtle and complex process. It took a thousand years to develop the stabilization serums. Our physicians regarded ageing as a disease, the drying, withering disease, and so attacked it as a disease. They did not regard it as, say a curse, or a punishment, or something inalterable or inexplicable, say, as some sort of destined, implacable fatality. No. They regarded it as a physical problem, susceptible to physical approaches. Some five hundred years ago, they developed the first stabilization serums."
"How could I ever pay for such a thing!," I gasped. 
"There is no question of payment," he said. "They are given to you as an animal, a slave."
"Master, I whispered," awed. 
"Do not fret," he said. "In the case of a woman from Earth, like yourself, they are not free." 
"Master?," I asked. He took my collar in both hands, and moved it in such a way that I could feel how sturdily, and obdurately, it was locked on my neck. 
"For a woman such as you," he said, "their price is the collar."
--Dancer of Gor pg. 472-473