My only condition right now is 'pre-hypertension'. over the past year or 2 i've been prescribed hctz, (hydrochlorothiazide) triamterene/hctz , and lisinopril/hctz. do these pills lose effectiveness past their 'use buy' date?

Expiration date: Medications past their expiration date likely have some activity, however the manufacturer is only promising efficacy through a specific date. A few medications can be toxic when kept too long. If you have old prescriptions because you have not taken them as directed, and now plan to hew to taking medication faithfully, turn over a new leaf and get a new bottle.