San Pedro is one of the fastest growing cacti. That said, it can take several weeks for first growth after planting a cutting, and if grown in good conditions one meter a year is considered a pretty solid rate of growth once it starts growing. 3 months isn't long enough to say for sure if anything is wrong with the cactus based on growth rate. If it doesn't gain a noticeable amount of mass in a full season, then maybe it's time to worry.
Also, correct me if I'm wrong, but trichocereus cacti mostly grow in the warm months and rest in the cold months, right? If it's three months old that means you planted it in January - it hasn't even had a growing season yet.
Growing something like weed is rather different - it's a water-loving, rapid growth plant, that's how it earned the nickname 'weed' after all - it grows like one

Cacti evolved to tough out those harsh dry seasons in desert climates, not to grow rapidly and die rapidly.
Peyote is one of the most difficult plants to grow. It also takes several times longer. Plus, in the US at least, the plant itself is explicitly scheduled in addition to the mescaline it produces, so it's far "more illegal" in that sense than growing peruvian torch or san pedro.