hello there MK,and thanks for writing to HCM i have read your query and understand whether THC can form cysts in the body and effects of marijuana. I would discourage usage of marijuana,however. Coming to your query,THC or tetrahydrocannabinol is the active ingredient which causes psychological effects and highs of marijuana that is derived from cannabis sativa marijuana as an entity rather than thc has caused a very few cases of lung cysts and splenic cysts(extremely rare) and association has been inconclusive so far. marijuana as i said affects psychologically ,while some side effects may last for longer period please understand side effects outweigh the few medical benefits in its usage. it causes dizziness,affects brain function of learning ,cognition,memory,causes hypotension,affects liver functions,can cause bleeding tendency,rare incidences of cysts,and has a lot of interaction with alcohol and many other drugs. avoid thc as far as possible.Hope it clarifies and helps your query. Good day