“Weed today isn't what it used to be”
People who say that are probably referring to the potency of modern marijuana compared to what it used to be, decades ago. Reports show that pot in the 1960's and 1970's had THC levels in and around 1%. Today the herb you're smoking has significantly more THC, with levels averaging more than 6-8% and some specially grown plants containing levels as high as 50%!
What's changed between then and now?
In the 1970's the majority of cannabis was imported illegally from outside countries, mainly Columbia. Cannabis potency is affected by oxidation. Imports from outside the country might take some long months to arrive. A period of time during which the crop was exposed to high temperatures that would serve to reduce it's potency. The journey from farm to patient has now been significantly reduced with most cannabis grown domestically of late.
In the 1980's hydroponic systems and in turn, hydroponic weed, became very common in the U.S. Hydroponics is a subset of hydroculture, the method of growing plants without soil, using nutrient enriched solutions or materials instead.
This method led to a moderate spike of potency in our marijuana. People were now able to grow weed closer to home, ultimately giving them access to fresher product(s). The ability to harvest cannabis on a local level meant the beginning of higher quality cannabis and best of all, the development of new strains.
With the indoor grow revolution of the 80's came hybridized strains. Hybridization consists of combining one or more indigenous varieties to create a new strain of the plant. Growers have been hard at work on creating better strains over the last few decades. It is only by crossing high potency strains that they have been able to increase the amount of THC in the plant.
The spikes in THC levels today can also be attributed to better growing climate conditions and how cannabis is now harvest processed and harvested.
In the past cannabis that was available was a healthy mix of leaves, stems and flowers. So the hippies weren't always consuming parts of the plant rich in THC. Dispensaries today sell product that contains more of the feminized flower (sinsemilla) which contains higher THC levels and a better quality product.
Marijuana is more potent today
As technology advances and specialized strains are created, the potency of cannabis continues to grow. This plus the fact weed can now be sourced closer to home are making all the difference when your friend tells you "weed today ain't what it used to be"
Instead, the plant and the surrounding culture have developed and matured while cannabis laws and prohibition begin to ease and roll back. A trend we expect will continue long after we see the end of prohibition in this country.
As marijuana goes increasingly mainstream—and, crucially, develops into big (and legal) business—more and more super-potent novelty strains are likely to crop up at the same time the distance from farm to user will be decreasing to all time low(s). We expect a modest continuation of this increased potency trend.