The physical implants behave in the same manner as the Intense Training perk, permanently raising a single statistic by one, except the implants in the add-on Old World Blues, many of which strengthen the player in various ways. Although implants can be bought when a statistic is at 10, they will confer no benefit.
The number of implants that can be installed by Dr. Usanagi is equal to the player's Endurance. Only the permanent base Endurance score is counted; boosts from drugs and apparel don't help. Although the boost from the Endurance implant is permanent, it doesn't entitle you to an additional implant. Raising Endurance with Intense Training does allow an additional implant. Implants from add-ons don't respect or count against this limit.
Since the effects of implants bought from Dr. Usanagi are counted as a permanent increase to your SPECIAL, they will affect the perks available to the player.
Doctor Usanagi sells implants to augment your physical abilities, and two special implants to augment the player's combat performance. Only one of each type can be installed. Installing an implant takes 3 hours of in-game time each.
A permanent unmodified Endurance of 9 will guarantee you the ability to get every implant. An Endurance of 7 will allow you to get all SPECIAL increasing implants. Raising Endurance by means of the Intense Training Perk or by allocating the one point bonus by concluding the Lonesome Road add-on will count towards this allowance, buying the Endurance Implant does not, although that raise is permanent for all other applications.
In normal mode, the PHOENIX Monocyte Breeder implant can effectively replace the need to sleep in order to regain health. Waiting will restore 12 HP an hour, or 288 HP in 24 hours, meaning it will often only take a single day of waiting to restore health. It also restores health during fast travel.
If the player has an INT stat of 3 or below, he/she will be offered a dialogue option of: "You sell plants, too?". Usanagi will explain what she really sells, then offer the Intelligence implant for a reduced price. Lowering the INT stat only temporarily by Chems makes the dialogue option available but does not entitle you to the discount, even if administered before making first contact with Dr. Usanagi.
xbox360pc If you are offered the low-intelligence discount but do not purchase the intelligence implant and then you leave the hospital, when you return and speak to Usanagi next time she will no longer offer this implant - discounted or otherwise.