From Brotato Wiki
Medikit
Item
Tier 4
Stats
+10 HP Regeneration
+2 HP Regeneration every 5 seconds until the end of the wave
-10 Luck
+2 HP Regeneration every 5 seconds until the end of the wave
-10 Luck
Price
95
Unlocked by
Win a run with 
Doctor
DoctorItem
Medikit is an in-game item that can be bought from Shop or can be found in a Crate. Most Items increase the Stats of the player while some of them provide unique effects.
Notes
The Medkit gives a base +10 HP Regeneration and an additional +2 HP regeneration per 5 seconds of time that has passed during a wave. This additional HP Regeneration lasts until the end of the wave.
You can see in the table below what this bonus is at different times during the wave:
| Time Passed | 0 | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 | 75 | 80 | 85 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Additional HP Regeneration | +0 | +2 | +4 | +6 | +8 | +10 | +12 | +14 | +16 | +18 | +20 | +22 | +24 | +26 | +28 | +30 | +32 | +34 |
This makes the Medkit very potent at healing during the 90 second Boss Fight on Wave 20.