Ive had seeds a few times in the past, and I'd have to agree with mongman about the variance in strength. The first time I just "tested the water" with around 170g of seeds, and felt sweet fuck all. The next time I got the same brand, same amount and was planning on doin an extraction on 340g. However, having already read about the huge variance, I decided against this and instead only used 170g again. This time the effects felt to be atleast twice as strong, felt nauseaus unless I was laying down not moving. It reminded me of high doses of codeine or tramadol, though not as enjoyable due to the more apparent nausea.
I've read seeds obtained from the poppies in Tasmania are lower in morphine and higher in (something less enjoyable with more nausea, cant remember the name atm). Seeds obtained from internationally are said to be higher in morphine content.