OK, I found this. It seems that the drug causes seed to sprout polyplidal plants, which are basically the 'double muscled belgian blue' bastards of the cannabid world this....
"You can employ a growth changer called Colchicine. This is a bit hard to get and expensive. (Should be ordered through a lab of some sort and costs about $35 a gram.)
To use the Colchicine, you should prepare your presoaking solution of distilled water with about 0.10 per cent Colchicine. This will cause many of the seeds to die and not germinate, but the ones that do come up will be polyploid plants. This is the accepted difference between such strains as "gold" and normal grass, and yours will DEFINITELY be super weed.
The problem here is that Colchicine is a poison in larger quantities and bay be poisonous in the first generation of plants. Bill Frake, author of CONNOISSEUR'S HANDBOOK OF MARIJUANA runs a very complete Colchicine treatment down and warns against smoking the first generation plants (all succeeding generations will also be polyploid) because of this poisonous quality.
However, the Medical Index shows Colchicine being given in very small quantities to people for treatment if various ailments. Although these quantities are small, they would appear to be larger than any you could receive form smoking a seed-treated plant."
Came from here
www.greenmanspage.com/guides/yield.html
But there's some pretty shitty advice on that page too. Like 'cut your light back to 14 hours a day to speed up finishing time' which is bollocks and makes no sense, and 'pinch off the end of all the leaves as the grow' to make the plant form a resin or hashy substance all over itself by completion. Again, sounds like rubbish to me.
Apparently, all you need to know is in that book, which is available on amazon.