It depends. It heals 15% of your total hitpoints, and it can go above your maximum hitpoints. It can heal up to 640 HP if you drink all four doses and have a hitpoints level of 99. :-)
assuming you have 10hp the answer would be level 75 but getting defence up usually means some hitpoints levels as well so if you wish to get 99 hitpoints as well you would be level 97.
Assuming you had 99 Hitpoints, and only had 1 Prayer, Summoning, Magic, and Ranged, you would have a combat level of 96.
15 hitpoints.
A lesser demon has 79 hitpoints
FINROCKS!
The Constitution cape can be purchased with the Constitution hood for 99k from Surgeon General Tafani at the Duel Arena by any player that has level 99 in Constitution. Constitution capes are white, and have a red trim if the player has more than one level 99 skill. The constitution cape was formerly known as the hitpoints cape until an update on 3 March 2010.
He Doesn't Have No Hitpoints, Just Destroy Is Little Friends First
a members creature that has 255 hitpoints is the kalphite queen and the K'ril Tsutsaroth
Fighting hill giants is the easiest way.
The brimhaven Agility Arena.
your best bet would be to play minigames, such as soul wars or pest control. Using any combat skills will get your hitpoints up. You can also use genie lamps, quest rewards, etc to train your hitpoints.