Haha no. What makes you think that? Benzos are pretty stable as a freebase. Methcathinone and some amphetamines aren't too great as freebase, methcathinone if made from pseudo can revert back to pseudo, but just turn them in to salt form, store somewhere dry and dark and should be all good. Make sure it's in powder/crystal form and not still in solution and as close to anhydrous as possible.
Heroin freebase stores well too, I've left some about 16 months and all was fine. I think if you dissolve it in water though it can hydrolyse back to morphine, although I dont think that is down to the acid/salt conversion but more so the water.
Cannabinoids can naturally decarboxylate in the right conditions but it takes a very long time. I've cooked 3.5 year old ganja and it still needed me to heat it to decarboxylate.
Pills have use by dates but these are more for legal reasons. I've drank morphine solution which was to be discarded 30 days after opening. I think it was at least 6 months past that.
There will be preservatives in the medicine.