Blood pressure drug tested to prevent transplant complication

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Diagnosis of: * Acute myeloid or lymphoid leukemia in remission, * Myelodysplastic syndrome, * Chronic lymphoid leukemia, * Non-Hodgkin lymphoma, * Hodgkin lymphoma, * Chronic myeloid leukemia in chronic or accelerated phase, * Myeloproliferative disorder, or * Multiple myeloma * Undergoing allogeneic HSC transplantation from a related or unrelated donor matched at least at 7 of 8 of the HLA-A, -B, -C, and DR loci ("8/8" or "7/8" match) * Undergoing allogeneic HSC transplantation after a myeloablative TBI-, busulfan-, or (non-myeloablative) melphalan-based pre-transplant conditioning regimen. Regimens for transplantation will include at one of the following agents, given in conjunction with fludarabine or cyclophosphamide: * Busulfan 130 mg/m2 iv daily x 2 (reduced intensity) or 4 days * TBI 150 cGy bid x8 doses (1200 Gy) * Melphalan 140 mg/m2. (Although melphalan is not a myeloablative regimen, it results in clinically significant mucositis and patients receiving this medication will be of considerable interest in the analysis of these data.) * Male or female patient age 18 years or older * Karnofsky performance status \> 70% at time of initiation of pre-transplant conditioning * Transplantation-specific co-morbidity score of \<5 at time of initiation of pre-transplant conditioning * Patients taking antihypertensive medications (including telmisartan) are eligible but the patient must discontinue treatment at least 48 hours prior to first dose of study medication * Capable of giving informed consent and having signed the informed consent form Exclusion Criteria: * Inability to provide informed consent * Subjects with known heart failure, advanced renal impairment requiring renal replacement therapy, or liver failure although these patients would most likely not be eligible for HCT. * Subjects taking ACE inhibitors, potassium supplements, or spironolactone (or any other potassium-sparing diuretics) who cannot discontinue use prior to initiation of study treatment OR who require a high-potassium diet * Patient unable to discontinue current hypertension medication for medical or other reasons for two days prior to starting telmisartan * Chronic symptomatic hypotension, volume depletion.