Tramadol is shady AF. Codeine is purely a prodrug, DHC is actually active in it's own right. The liver (and brain) convert codeine to morphine but it is a rate-limited step which is why medically 240mg of codeine is the maximum prescribed.
Oddly, the liver enzyme production can be hugely speeded up by the old-school hypnotic glutethimide and in the US, people used to take 240mg of codeine (4 x Tylenol '#4) and 900mg of glutethimide (3 x Doriden) to produce an effect the aficionados compared to H.
It was a rare and crazy scene. Dealers who would smurf 'tame' doctors for Doriden and Tylenol #4 scripts. 'Dealer to the stars' is the kind of thing I mean. People who only trust medicines and who are prepared to pay way over the odds to get the best psychoactive medicines.
