There has been little research into contamination levels over time; however there have been several cases reported in Australia and overseas where tenants have become sick after living in contaminated properties (unbeknown to them). This can occur months and even years after the meth lab is gone.
Methamphetamine is usually the least toxic of the chemicals found in a meth house – however its usually the hardest to clean up. The chemical precursors (of which there can be up to 32) are the more concerning when it comes to toxicity and ability to stay present for longest.