NPH Insulin (Humulin N)
NPH (Neutral Protamine Hagedorn) insulin is an intermediate-acting suspension of human insulin with protamine, giving onset in ~1-2 hours, a peak at 4-8 hours and ~12-16 hour duration. Its pronounced peak makes it a classic but especially hazardous bodybuilding insulin.
01 Overview
NPH combines human insulin with protamine and zinc to slow absorption, producing a distinct peak several hours after injection. It has been a mainstay of diabetes therapy for decades and is available over the counter in many US states.
Unlike peakless basal analogues, NPH's mid-action surge can catch users off guard, causing unexpected hypoglycaemia hours after dosing when carbohydrate has run out. This delayed, peaking action is a frequent cause of severe lows in physique misuse.
02 Mechanism
Binds the insulin receptor to drive glucose uptake and anabolic signalling; protamine-zinc complexation delays dissolution, giving a delayed onset and a defined peak at 4-8 hours.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Low (off-label) | 3–8 IU | SubQ | Beware delayed peak; extreme caution |
| Diabetic basal | 10–30 IU | SubQ | Once or twice daily; individualised; medical use only |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Extended glycogen/nutrient uptakeProlonged action supports sustained glucose disposal into muscle. | Clinical | ||
| Anabolic / anti-catabolic signallingSupports protein synthesis over an extended window. | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Fat gain / lipohypertrophyAdipose gain and injection-site lumps. | Mild | Common | Clinical | |
| Delayed peak hypoglycaemiaA sharp glucose fall at the 4-8 hour peak, often after carbohydrate has been exhausted, can cause seizure, coma or death. | Life-threatening | Common in misuse | Clinical |